当前期刊: Proceedings of the Institution of Mechanical Engineers Part C-Journal of Mechanical Engineering Science Go to current issue    加入关注   
显示样式:        排序: 导出
我的关注
我的收藏
您暂时未登录!
登录
  • Theoretical and experimental investigations on nano-finishing of internal cylindrical surfaces with a newly developed rotational magnetorheological honing process
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-09-25
    Sunil K Paswan; Anant K Singh

    In the current scenario, the advanced industries are using highly sophisticated types of machinery. These types of machinery use numerous cylindrical components made with superior materials and technology. For obtaining the nano-level finished interior cylindrical surface with high accuracy and high production rate, a newly developed rotational magnetorheological honing (R-MRH) process is employed on the cylindrical objects. This process is applicable in internal nano-finishing of cylindrical molds, hydraulic and pneumatic valves, aerodynamic bearings, gears, cylindrical barrel, and cylinders used in medical devices, etc. In the present work, the cylindrical workpiece is also made rotational in the reverse direction of the MRH-tool rotation unlike the existing MRH process. The rotating motion of the workpiece cylinder caused an increment in relative motion of the active abrasive particles against the interior surface of the workpiece cylinder. The effect of the rotational speed of the workpiece cylinder along with movements of the MRH-tool on change in surface roughness is investigated theoretically and experimentally in this work. Theoretically, it is found that the simultaneous motions of tool and cylindrical workpiece in the opposite direction to each other increase the finishing rate. To validate the theoretically increased finishing rate due to the rotating cylindrical workpiece, and to examine the effect of the rotational motion of the cylindrical workpiece on finishing performance, the experiments are conducted with the R-MRH process. The reduction in surface roughness is found as 71.71% in 60 min with the existing MRH process for the stationary cylindrical workpiece, whereas it is reduced to 83.83% in only 40 min with the R-MRH process for the rotational cylindrical workpiece. The significant change in surface roughness value with reduced finishing time validates the improved efficacy of present R-MRH process for its more utility in industries.

    更新日期:2020-01-09
  • Optimization of steaming, drying, and tempering pretreatments for improving shelling of extra-large cashew nuts
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-09-22
    Son Doan Tran; Tra Thu Thi Tran; Minh Cong Tong; Naoki Uchiyama

    In this research, the response surface methodology with a polynomial model was used to represent the experimental data of the combination of steaming, drying, and tempering process for extra-large cashew nuts. The desired values of pre-treatment conditions minimize the broken kernel percentage and maximize the shelling capacity to achieve cost effectiveness. In the this study, the steaming, drying, and tempering conditions were optimized for the minimization of the broken kernel percentage and the maximization of the shelling capacity of extra-large cashew nuts (bigger than 32 mm). The optimal conditions were steaming temperature at 100 ℃ for 38 min, then drying at 70 ℃ for 30 min, and finally tempering for 4 h. Under these conditions, the minimal broken kernel and maximal shelling capacity achieved were 2.45 ± 0.24% and 14.58 ± 0.35 kg/h, respectively.

    更新日期:2020-01-09
  • Investigation on thrust force in rotary ultrasonic drilling of CFRP/aluminum stacks
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-09-24
    Song Dong; Wenhe Liao; Kan Zheng; Wenrui Ma

    The stacks of carbon fiber-reinforced polymer (CFRP) and aluminum are widely used in aviation industry due to its excellent mechanical and physical properties. Recently, rotary ultrasonic drilling technology which is recognized as a useful machining method has been introduced to machining these stacks. Thrust force influences the machinability directly such as tool wear, cutting temperature, and hole qualities. In this study, a theoretical model of thrust force for rotary ultrasonic drilling of CFRP/aluminum stacks is proposed. Based on the analysis of kinematic characteristics, the axial uncut chip thickness of rotary ultrasonic drilling is presented. Then the whole machining process of stacks is divided into five different states. Forces on cutting edge and chisel edge in different materials are modeled, respectively. After that, the thrust forces of five-state rotary ultrasonic drilling process are achieved by integrating with integral limits analysis in each state. Finally, verification experiments are conducted, and experimental results show that the trends of thrust forces agree well with the thrust force model. Therefore, this theoretical model can be used to evaluate the thrust force in rotary ultrasonic drilling of CFRP/aluminum stacks.

    更新日期:2020-01-09
  • A novel engagement-pixel image edge tracking method for extracting gear tooth profile edge
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-09-24
    Jie Lu; Zhiqin Cai; Bin Yao; Binqiang Chen

    Accurate gear profile plays an important role in determining the transmission performance of gear-drive equipment. In this paper, a novel method for extracting gear tooth profile edge is presented. The presented method is based on engagement-pixel image edge tracking (EPIET) technique, and does not rely on the traditional meshing theory. An algorithm for the proposed method is put forward. Firstly, instantaneous contact images between the envelope curves of the gear profile and the instantaneous locus of the cutting tool are acquired. Secondly, pixels on the boundary of the envelope curves are lighted and the instantaneous locus coordinates of the cutting tool are calibrated. Lastly, the pixel coordinates of instantaneous meshing points are extracted, based on the fact that there is exactly one contact point per instant, and major error sources of the presented method are discussed. To verify the effectiveness of the presented method, a case study is conducted on a face gear, which is a type of complex conjugate gear, to extract its tooth profile edge. In the study, the tooth profile error and the contact line error are investigated. The results demonstrate that the presented method, without knowing complicated meshing equations, can acquire feasible accuracy and stability, compared with traditional meshing equations. It is shown that the novel method can be extended to applications of digital design of complex conjugate curved surfaces, in a simple and fast manner.

    更新日期:2020-01-09
  • Mechanical structural design based on additive manufacturing and internal reinforcement
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-09-25
    João Fiore Parreira Lovo; Italo Leite de Camargo; Luis Antonio Oliveira Araujo; Carlos Alberto Fortulan

    The design of modern mechanical components often requires the use of low-density and high-strength parts. Additive manufacturing presents competence in obtaining format complexity internally (voids, ducts, channels) and externally (shape, holes). However, parts obtained by material extrusion additive manufacturing are highly anisotropic and relatively weak. This paper aims to present a new mechanical design technique that combines the high geometry flexibility of additive manufacturing with internal structuring reinforcement by high-strength materials, which enables optimized parts with reinforcement in the most mechanical stressed areas during service, through adopting structured internal geometry filled with reinforcement material. Dense test specimens and test specimens with internal structural canals filled with reinforcement material (epoxy resin and carbon fibers) were designed, fabricated and tested physically and virtually. The obtained results provide property values for 3D-printed acrylonitrile butadiene styrene (typical material of additive manufacturing) and for this polymer reinforced with various reinforcement material configurations (useful for mechanical design). The reinforcement decreased anisotropy and improved mechanical properties. Optimized parts filled with resin and long carbon fibers had maximum flexural resistance of 112 MPa, with a specific weight of 1.1 g/cm3. This reinforcement provided parts with specific flexural strength similar to structural aluminum alloys, preserving the geometry and external dimension of the printed parts. The technique presented here shows the possibility of new conceptions in mechanical components design and strength optimization by internal reinforcement canals in parts. The technique is useful for mechanical design activity and allows for new product conceptions based on additive manufacturing.

    更新日期:2020-01-09
  • Stability analysis of rigid rotors supported by gas foil bearings coupled with electromagnetic actuators
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-09-25
    Kamal Kumar Basumatary; Gaurav Kumar; Karuna Kalita; Sashindra K Kakoty

    Rotors supported on gas foil bearings have low damping characteristics, which limits its application. A possible solution could be an integration of a gas foil bearing with an electromagnetic actuator. This paper discusses the effect of electromagnetic actuators on the stability of a rotor supported on gas foil bearings. A coupled dynamic model combining the dynamics of gas foil bearing and electromagnetic actuator has been developed. The fluid film forces from the gas foil bearings and the electromagnetic forces from the electromagnetic actuators are integrated into the equations of motion of the rotor. The sub-synchronous vibration present in case of conventional gas foil bearings is reduced and the stability band of the rotor is increased due to the implementation of electromagnetic actuator.

    更新日期:2020-01-09
  • Contact stiffness ratio of tribological interface using the equivalent thin layer and the micro-slip model
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-09-29
    Yunyun Sun; Huifang Xiao; Jinwu Xu

    In this paper, a method for evaluating the contact stiffness ratio of the elastic rough interface is proposed. The rough contact interface subjected to normal load is replaced by an equivalent thin layer with isotropic material. The interfacial stiffness ratio is characterized using the material parameters of the thin layer. The shear modulus and Young’s modulus of the thin layer are determined by introducing the stuck length coefficient combined with the micro-contact analysis of the deformed asperity. The derived stiffness ratio is related to the surface topography, interfacial separation, material properties of the contacting bodies, and the stuck length coefficient. The implicit solution of the stuck length coefficient is also obtained. Variations of the stiffness ratio with the interfacial separation and the normal force are analyzed for different surface topographies and stuck length coefficients. Comparisons between the interfacial stiffness ratio of the proposed method and the experimental results as well as the calculated values of existing models are performed.

    更新日期:2020-01-09
  • Theoretical study on the effect of the anti-yaw damper for rail vehicles
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-10-01
    Zhanghui Xia; Jinsong Zhou; Dao Gong; Wenjing Sun; Yu Sun

    Simplification of a complex model is an analytical method commonly adopted in engineering design and academic research. A simplified theoretical analysis model can help project planners or researchers to develop an integrative view of the effect of each component on the system performances, which allows them to understand the related engineering phenomena and make proper engineering judgments. Based on the widely used Maxwell constitutive model for anti-yaw dampers, a simple 4 degree-of-freedom model is established to derive a set of analytical formulas, including those for critical speed, anti-yaw damper force transfer function, and rational resistance factor, which control the stability, ride quality, and curving performance of rail vehicles, respectively. Based on the proposed analytical formulas, the impact of damper parameters and mounting positions of the anti-yaw damper on the stability, ride quality and curving performance are analyzed. Finally, trade-offs among stability, ride quality, and curving performance are also discussed.

    更新日期:2020-01-09
  • State of the art in tilt-quadrotors, modelling, control and fault recovery
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-10-15
    Ismail Al-Ali; Yahya Zweiri; Nawaf AMoosa; Tarek Taha; Jorge Dias; Lakmal Senevirtane

    Research studies on quadrotors have recently drawn significant interest from academia and industry. Faults and failures handling are the major weaknesses of conventional quadrotor platforms; therefore, an innovative actuation mechanism was introduced to allow tilting the rotors. Tilting rotors of multirotor platforms provide high dexterity for flying between adjacent obstacles and assist the platforms in dealing with various failure scenarios. This paper reviews the state of the research on tilt-quadrotor platforms. Several platforms, software and hardware architectures, were discussed in the literature. Most of the latest developments were focused on conventional quadrotor modelling, combined with rotor tilting dynamics. On the other hand, controlling such platform was mainly studied using two types of controllers: Feedback Linearisation technique and Control Allocator. Recovery strategy in case of fault or failure has been covered extensively for conventional quadrotors, but very limited known work for tilt-quadrotor. This review concludes that the system dynamic modelling is relatively well covered compared to exploring new control techniques for more stringent requirements. However, recovery strategies as the main advantage of tilt-quadrotor platforms are not explored extensively and require more research attention.

    更新日期:2020-01-09
  • Design and experimental research on electromagnetic active suspension with energy-saving perspective
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-10-21
    Jiajia Wang; Long Chen; Ruochen Wang; Xiangpeng Meng; Dehua Shi

    A hydraulic damper can improve system reliability when it is introduced to an electromagnetic active suspension equipped with a linear motor. In this study, the effect of damping value on the energy consumption of an electromagnetic active suspension system is investigated with an energy-saving perspective. A kinetic model of electromagnetic active suspension is established, and a controller is designed on the basis of a linear quadratic regulator. Three different levels of roads are then chosen as driving conditions, and the corresponding control targets are set. The effects of damping value on energy consumption and dynamic performance of electromagnetic active suspension under different driving conditions are determined. Results show that damping value does not affect dynamic performance at the same weighting factor or the same driving condition in a time domain. Compared with that of an electromagnetic active suspension without a damper in parallel, the energy consumption of the electromagnetic active suspension system initially decreases and subsequently increases as the damping value increases. Therefore, appropriate damping values can significantly reduce energy consumption. In a frequency domain, appropriate damping values can improve driving safety but can slightly deteriorate ride comfort. An integrated electromagnetic actuator is also designed by integrating the linear motor with the hydraulic damper to construct a practical system structure. These parameters are optimized to improve air-gap magnetic field strength. Thus, the initial design of the structure and dimension of the electromagnetic active suspension system is completed. Finally, the prototype is produced and a 1/4 bench test is also conducted to verify the correctness of theoretical research.

    更新日期:2020-01-09
  • Adaptive fault-tolerant control for active suspension systems based on the terminal sliding mode approach
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-10-25
    Amirhossein Kazemipour; Alireza B Novinzadeh

    In this paper, a control system is designed for a vehicle active suspension system. In particular, a novel terminal sliding-mode-based fault-tolerant control strategy is presented for the control problem of a nonlinear quarter-car suspension model in the presence of model uncertainties, unknown external disturbances, and actuator failures. The adaptation algorithms are introduced to obviate the need for prior information of the bounds of faults in actuators and uncertainties in the model of the active suspension system. The finite-time convergence of the closed-loop system trajectories is proved by Lyapunov's stability theorem under the suggested control method. Finally, detailed simulations are presented to demonstrate the efficacy and implementation of the developed control strategy.

    更新日期:2020-01-09
  • Influence of system parameters on buckling and frequency analysis of a spinning cantilever cylindrical 3D shell coupled with piezoelectric actuator
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-11-04
    Ali Shokrgozar; Hamed Safarpour; Mostafa Habibi

    In this research, buckling and vibrational characteristics of a spinning cylindrical moderately thick shell covered with piezoelectric actuator carrying spring-mass systems are performed. This structure rotates about axial direction and the formulations include the Coriolis and centrifugal effects. In addition, various cases of thermal (uniform, linear, and nonlinear) distributions are studied. The modeled cylindrical moderately thick shell covered with piezoelectric actuator, its equations of motion, and boundary conditions are derived by the Hamilton's principle and based on a moderately cylindrical thick shell theory. For the first time in the present study, attached mass-spring systems has been considered in the rotating cylindrical moderately thick shells covered with piezoelectric actuator. The accuracy of the presented model is verified with previous studies. The novelty of the current study is consideration of the applied voltage, rotation, various temperature distributions, and mass-spring systems implemented on proposed model using moderately cylindrical thick shell theory. Generalized differential quadrature method is examined to discretize the model and to approximate the governing equations. In this study, the simply supported conditions have been applied to edges θ=π/2,3π/2 and cantilever (clamped–free) boundary conditions has been studied in x = 0, L, respectively. Finally, the effects of the applied voltage, angular velocity, temperature changes, and spring-mass systems on the critical voltage, critical angular speed, critical temperature, and natural frequency of the structure are investigated.

    更新日期:2020-01-09
  • Performance and noise analysis of vibratory feeder using dynamic rubber spring model
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-10-25
    Chitransh Singh; Madan Lal Chandravanshi

    In vibratory feeder, material feeding occurs due to the vibration of a trough mounted on helical springs. High vibration amplitude of trough causes the springs to jump and usually results in higher noise level generation and increase in force transmissibility in the support structure of the feeder. Reducing this noise without having significant changes in the dynamics of the feeder unit is a major challenge in the present industries. This paper presents a dynamic rubber spring model for vibratory feeders to reduce the noise level and the force transferred to the support structure of the feeder. Measurement of dynamic parameters such as vibration amplitude and magnitude of force transmitted to support structure, noise level, and conveying speed of particle analyses have been conducted experimentally on vibratory feeder with and without rubber gasket installed at spring support structure. The use of rubber gaskets at spring supports and their implication on force transmissibility and noise level of feeder is established experimentally. The performance analysis of feeder was also conducted using particle conveying speed on trough for different setups of feeder unit. It was found that the introduction of rubber gaskets at spring supports of the feeder increases the system damping, which helps in noise reduction as well as reduced amplitude of vibration and higher acceleration of trough. The increased acceleration leads to higher particle conveying velocity on the feeder trough.

    更新日期:2020-01-09
  • Fluid flow analysis of a turbulent offset jet impinging on a wavy wall surface
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-10-14
    Tej Pratap Singh; Amitesh Kumar; Ashok Kumar Satapathy

    The fluid flow characteristics of a turbulent offset jet impinging on a wavy wall surface has been investigated numerically. Two-dimensional Reynolds-averaged Navier–Stokes (RANS) equations are solved by the finite volume method. In the governing differential equations, the convective and diffusive terms are discretized by the power law upwind scheme and second-order central difference, respectively. The semi-implicit method for pressure linked equation algorithm is utilized to link the pressure to the velocity. The offset ratio is set to 7.0 and the Reynolds number is fixed to 15,000. The width of the jet is taken as the characteristic length. The amplitude of the wavy wall surface is varied from 0.1 to 0.7 with an interval of 0.1 and the number of cycle is fixed to 10. The results of fluid flow and turbulent characteristics of the offset jet are presented in the form of contours of streamline, velocity vector, turbulent kinetic energy, dissipation rate, pressure, and Reynolds shear stress. The variation in integral constant of momentum flux, wall shear stress, and pressure along the wall is presented and also compared. The decay in the maximum streamwise velocity in the downstream direction and jet half-width along the streamwise direction are also presented and discussed. The wavy surface introduces some remarkable features, which are not present in a normal plane wall case. These features have been discussed in detail.

    更新日期:2020-01-09
  • A new model of industrial internet of things with security mechanism—An application in complex workshop of diesel engine
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-11-03
    Jiangshan Liu; Ming Chen; Liang Wang

    Intelligent manufacturing is the future development direction of manufacturing industry. There are still some problems lurk in the traditional mode of production, such as “information island” and “network security”, which result in low productivity but high-cost production, and information leakage. With application of the new generation information technology in manufacturing field is expanded, the deep integration of information technology and manufacturing industry promotes the development of production towards intellectualization, networking, and service. Single mode of production is gradually replaced by the way of large-scale collaborative production, so the traditional industrial internet of things (IoT) and manufacturing architecture are not suitable for the needs of actual production any more. For instance, the great challenges of compatibility and coordination of interface protocols, huge data, cost, and safety. In order to solve these problems, a new model of industrial IoT with security mechanism used in intelligent workshop is proposed. Firstly, this article analyzes the current situation of manufacturing industry and information technology, a secure transmission model of industrial IoT was designed based on the new generation information technology. Secondly, combined with the structure of the IoT and the real production demands, a six-tier industrial IoT architecture based on the new generation information technology is proposed. Finally, the three dimensions of the intelligent manufacturing model are expanded according to the architecture of the IoT. Not only a six-tier intelligent manufacturing system framework based on the new generation of information technology is obtained, but also the network security mechanism is introduced. On one hand, it realizes the coordinated operation of industrial chain, supply chain, and value chain of production process, on the other hand, it also improves the networking, intellectualization, and service level of industrial production. What is more the system can also provide the reference model for the various application of IoT.

    更新日期:2020-01-09
  • Nonlinear free vibrations analysis of overhung rotors under the influence of gravity
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-10-25
    M Moradi Tiaki; SAA Hosseini; H Shaban Ali Nezhad

    In this paper, nonlinear free vibration of a cantilever flexible shaft carrying a rigid disk at its free end (overhung rotor) is investigated. The Rayleigh beam model is used and the rotor has large amplitude vibrations. With the assumption of inextensibility, the effect of nonlinear curvature and inertia is considered. The effect of disk mass on the dynamical behavior of the system is studied in the presence and absence of gravity (horizontal and vertical rotors). By using perturbation technique (method of multiple scales), the main focus is on the influence of gravity on equations of motion and on quantities such as amplitude and damped natural frequency. Here, a different behavior is observed due to the rotor weight. Indeed, the combination effects of gyroscopic term, nonlinearity and gravity are studied on the modal behavior of the system. It is shown that the static deflection creates second order nonlinear terms and changes the nonlinear damped natural frequency. With considering of gravity, both beat and high frequency in beat phenomenon increase. With increasing of the rotor weight, the minimum value of amplitude is extremely amplified in the direction of gravity but in the other transverse direction, amplitude of vibrations decreases. In addition, it is found that the weight has directly influence on beat frequency, while the mass ratio between disk and beam affects the high frequency.

    更新日期:2020-01-09
  • One-dimensional analyses of striker impact on bar with different general impedance
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-09-30
    Hyunho Shin; Daesung Kim

    The particle velocity and stress in the striker and bar generated by the striker impact on a bar with different general impedance are formulated based on one-dimensional assumptions. Departure of the impact-generated stress wave towards the rear end of the striker and arrival of the release wave from the rear to the front of the striker constitute one impact cycle. In cases where Zs ≤ Zb (Z is the general impedance, and subscripts ‘s’ and ‘b’ denote striker and bar, respectively), only one impact cycle takes place because the striker is stationary or separated from the impact surface after the first impact cycle. As a result, only a single (primary) pulse is observed in the bar and striker. In the case where Zs > Zb, however, multiple impact cycles take place because the striker is compressing the bar continually after the first cycle. As a result, a series of step-wise residual pulses follow the primary pulse in the bar and striker. The magnitudes of the stress and particle velocity in the bar and striker calculated using the formulated equations are quantitatively consistent with the results of the numerical simulations, verifying the formulated one-dimensional equations. The equations formulated in this study may be useful for better understanding the various wave interaction phenomena that take place in a pseudo-one-dimensional impact system and for modifying/designing an impact system.

    更新日期:2020-01-09
  • Axisymmetric indentation problem of a transversely isotropic elastic medium with surface stresses
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-09-29
    Fang Fang Wang; Jing Jin Shen; Yong Gui Li

    The frictionless contact problem between an axisymmetric rigid indenter and a layered transversely isotropic medium with surface stresses is considered. The contact pressure is represented as a product of two series based on the solutions of the bulk material and the elastic surface. By using Hankel transforms, the coefficients in the product-series representation are determined by the normal displacement condition inside the contact area and the finite-pressure condition at the contact edge. Taking the spherical indentation as a specific example, the effectiveness of the solution procedure is verified for various contact scenarios. Comparing with the Green’s function method, this solution procedure is not only computationally efficient but also may give the contact pressure in its analytical form. For some specific problems, the effects of the material anisotropy and the layer thickness on the contact process with surface stresses are investigated.

    更新日期:2020-01-09
  • Analysis of heat affected zone (HAZ) during micro-drilling of a new hybrid composite
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-09-30
    Akshay Jain; Bhagat Singh; Yogesh Shrivastava

    In the present work, laser beam drilling of a fabricated basalt–glass hybrid composite has been done. From the experimental results, a safe machining zone pertaining to high drill quality with minimum heat affected zone and maximum hole-circularity has been predicted. The prediction of the zone has been done by mathematical modeling and optimization using artificial neural network merged with multi-objective genetic algorithm. The acquired zone has been confirmed by performing validation experiments. From the results, it is evident that the predicted range is capable of minimizing the heat affected zone with acceptable hole-circularity. Moreover, the variation in hole-circularity and heat affected zone with respect to the input drilling parameters has also been explored.

    更新日期:2020-01-09
  • Effect of temperature on properties of aluminum/single-walled carbon nanotube nanocomposite by molecular dynamics simulation
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-09-30
    Mohsen Motamedi; AH Naghdi; SK Jalali

    Composite materials have become popular because of high mechanical properties and lightweight. Aluminum/carbon nanotube is one of the most important metal composite. In this research, mechanical properties of aluminum/carbon nanotube composite were obtained using molecular dynamics simulation. Then, effect of temperature on stress–strain curve of composite was studied. The results showed by increasing temperature, the Young’s modulus of composite was decreased. More specifically increasing the temperature from 150 K to 620 K, decrease the Young’s modulus to 11.7%. The ultimate stress of composite also decreased by increasing the temperature. A continuum model of composite was presented using finite element method. The results showed the role of carbon nanotube on strengthening of composite.

    更新日期:2020-01-09
  • A simulation-based study on the effect of underwater friction stir welding process parameters using different evolutionary optimization algorithms
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-11-06
    Mohd A Wahid; Sarfaraz Masood; Zahid A Khan; Arshad N Siddiquee; Irfan A Badruddin; Ali Algahtani

    This paper investigates the effect of underwater friction stir welding process parameters on the mechanical properties of the aluminum alloy 6082-T6 joint and further simulates this process using various evolutionary optimization algorithms. Three independent underwater friction stir welding process parameters, i.e. shoulder diameter (in mm) at two levels, rotational speed (in r/min) at three levels, and traverse speed (in mm/min) also at three levels, were varied according to the Taguchi’s L18 standard orthogonal array. The effect of variations in these parameters, on the ultimate tensile strength (in MPa), percentage elongation (in %), and impact strength (in J) of the welded joint was experimentally measured and recorded. In order to simulate this underwater friction stir welding process, three evolutionary optimization algorithms, i.e. particle swarm optimization, firefly optimization, and non-dominated sorting established on the genetic algorithm (NSGA-II), were employed. In these simulations, an artificial neural network with two layers, resembling a non-linear function, was employed as the cost function to predict the values of the response variables, i.e. ultimate tensile strength, elongation, and impact strength, which were experimentally measured earlier. In these simulations, several experiments were conducted using different randomly selected data set and subsequently, the accuracy of each individual simulation was compared. Results revealed that the firefly optimization-based simulation performed the best with least mean squared error while predicting the response variable values, as compared to the particle swarm optimization and the NSGA-II. The minimum value of the mean squared error for the firefly optimization-based simulation was observed to be as low as 0.009%, 0.004%, and 0.017% for ultimate tensile strength, elongation and impact strength, respectively. Furthermore, it was also observed that the computational time for the firefly optimization-based simulation was significantly lower than that of both particle swarm optimization and NSGA-II-based simulations.

    更新日期:2020-01-09
  • Thermal error controlling for the spindle in a precision boring machine with external cooling across coated joints
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-10-09
    Mohan Lei; Gedong Jiang; Liang Zhao; Jinshi Wang; Ben Q Li; Ping Xia; Jun Yang; Xuesong Mei

    Spindles in precision boring machines usually operate without internal cooling, and thermal error in such spindles is nonnegligible and can severely affect the end-processing quality of the machines. This study aims to investigate the effects that external cooling exerts on the thermal behavior of such spindles. A helical tube cooler is taken for external cooling. An analytical thermal resistance model for the grease-coated cooler-housing joint surface, which considers the pressured cambered-flat contact pair and rough metal surface-grease contact, is presented and validated, and a numerical thermal–fluid–solid coupling model for the cooler-spindle system is then established. An evaluation method is put forward to obtain the stability of the thermal error, which determines the boring processing accuracy and thermal equilibrium time, from experimental data. Then, the external cooling was optimally designed based on the simulation results from the numerical model. Experiments show that the designed cooler reduced the thermal equilibrium time by 47.13% and the maximum thermal error by 81.7%, and the proposed model can accurately predict the cooling effect on the spindle thermal behavior. This study not only provides a thermal error control method for the spindle but is expected to advance the theoretical basis of cooling design for complex electromechanical systems.

    更新日期:2020-01-09
  • Analytical investigation on load-sharing characteristics for multi-power face gear split flow system
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-09-18
    Shuai Mo; Zongxiang Yue; Zhiyou Feng; Lijuan Shi; Zhenxing Zou; Heyu Dang

    The multi-power face gear split flow system is a new type of transmission system, which has the advantages of stable and reliable transmission and strong carrying capacity. And it has great potential in the application of helicopter transmission systems. In this paper, the multi-power face gear split flow system was taken as the research object. Based on the lumped parameter method and Newton’s second law, the translational-torsional dynamic model of the system was established considering the translational vibration and the torsional vibration of the gears, and the meshing force curves and load-sharing coefficient curves were drawn. At the same time, the factors affecting the load-sharing characteristics of the transmission system were studied. The impacts of manufacturing errors, assembly errors, manufacturing error phases, assembly error phases, meshing damping, support stiffness, and the input power on the load-sharing coefficients were analyzed. The research shows that the errors and error phases of spur gears have small impacts on the load-sharing coefficients, while the support stiffness of spur gears has a great impact on the load-sharing coefficients. The errors and error phases of face gears have small impacts on the load-sharing coefficients, while the support stiffness of spur gears has a great impact on the load-sharing coefficients. The load-sharing coefficients increase constantly with the increase in the meshing damping between face gears and spur gears, whereas the load-sharing coefficients decrease constantly with the increase in the input power.

    更新日期:2020-01-09
  • Meshing limit line of the conical surface enveloping conical worm pair
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-09-29
    Qingxiang Meng; Yaping Zhao; Zaiyou Yang

    In this study, the calculating principle of the meshing limit line of the conical surface enveloping conical worm pair is put forward systematically. The tooth face equations, the meshing function and the meshing limit function of a conical worm pair are all acquired. Investigating the meshing limit line is come down to solving an equivalent unary nonlinear equation, which is determined from its original equations with four variables by means of the elimination technique. Based on this, the meshing limit line characteristics are deeply researched after resolving preceding equation correctly. The numerical results declare that there may be two meshing limit lines on each helicoid of one tooth of an enveloping conical worm although not all of them have physical significance. All the significative meshing limit lines usually do not get into the worm helicoid and have no influence on its normal work. Therefore, the active length of the worm depends on the tooth face boundary of the conical worm wheel theoretically. Besides, when the center distance of the worm pair is less, the transmission ratio is larger and the number of thread of the worm is more, the meshing limit line may be closer to the little end of the conical worm e helicoid.

    更新日期:2020-01-09
  • Assembly interference and its avoidance of spiral bevel gears in cyclo-palloid system
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-10-22
    Isamu Tsuji; Kazumasa Kawasaki

    In this article, the assembly interference of spiral bevel gears in a Klingelnberg cyclo-palloid system is analyzed based upon tooth contact analysis and is investigated experimentally. Each backlash in increasing mounting distance of the pinion is calculated step by step, using developed tooth contact analysis. When the backlash increases, the assembly interference does not occur based upon the calculated results. When the backlash decreases and is less than zero, the assembly interference occurs. When the assembly interference occurs, the tooth surfaces should be modified in order to prevent the assembly interference. In this case, a method of the modification is proposed. The experimental results showed a good agreement with the analyzed ones. As a result, the validity of the analysis and avoidance of the assembly interference in this method was confirmed.

    更新日期:2020-01-09
  • A visco-hyperelastic constitutive model of short- and long-term viscous effects on isotropic soft tissues
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-09-22
    Zahra Matin, Ghahfarokhi; Mahdi Moghimi Zand; Mehdi Salmani Tehrani; Brianna Regina Wendland; Roozbeh Dargazany

    Understanding and modeling the constitutive behavior of soft tissues represents an important challenge with significant relevance in medicine and biology. In this paper, we propose a new visco-hyperelastic model to describe the constitutive behavior of soft tissues as an isotropic and homogeneous material. The model is based on the nonlinear framework of continuum mechanics. A generalized Rivlin strain energy and a short-term viscous strain energy are used to describe the elastic part and time-dependence viscous part, respectively, while a long-term viscous function is derived through an integral framework of the applied stretch. To calibrate the material parameters, a set of self-designed uniaxial compression and relaxation tests are carried out on cylindrical samples of bovine liver. Moreover, the model is also validated against the experimental data of synthetic tissues reported by Khan et al. The good agreement between the predicted results and experimental data establishes the relevance of the proposed model. To investigate the model reliability, we have developed a “user-defined materials” subroutine to implement the constitutive behavior of the liver tissue in ABAQUS. By using the model, we simulate in vitro bovine liver behavior under compression and in relaxation and study the relative effects of the hyperelastic and viscous components on liver biomechanics.

    更新日期:2020-01-08
  • Effect of fiber orientation on the milling performance of quartz fiber composites in cryogenic cooling
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-08-28
    Fengbiao Wang; Yongqing Wang

    Quartz-reinforced polyimide composite is a kind of material with anisotropic and nonuniform properties. The machinability has high dependence on fiber orientation θ. This paper presents the first comprehensive investigation on the cutting model of composites based on fiber orientation. A series of cryogenic cooling milling experiments were carried out to study the influence of fiber orientation on surface morphology, roughness, milling force, and tool wear. The results show that fiber orientation with acute angle has more advantages than obtuse angle. At the same time, it can provide effective chip breaking for latitude and longitude fibers at θ = 45° acute angle. Besides, when the tool is swept 96°, the milling force will reach the maximum, and the shearing effect of the latitude fiber is achieved maximum near θ = 60°. Similarly, the best surface quality is obtained where pits, crack, and burr defects are effectively restrained. Meanwhile, when the chosen cutting speeds are 50, 100, and 150 m/min, the roughness of 0.86 µm, 0.61 µm, 0.5 µm can be attained with θ = 48°, 55°, and 57°, respectively. Although the tool wear is relatively obvious when θ = 60°, the tool is still in a stable wear stage with better machining effect. Hence, it can be concluded that cryogenic cooling machining has better machinability and cutting effect at fiber orientation θ = 60° with larger milling parameters.

    更新日期:2020-01-08
  • Roadway piezoelectric energy harvester design considering electrical and mechanical performances
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-09-04
    Erfan Hamsayeh Abbasi Niasar; Masoud Dahmardeh; Hamed Saeidi Googarchin

    Piezoelectric energy harvesting is an efficient technique among energy scavenging methods employed in asphalt pavements. Several designs are reported in the literature; however, what is less discussed is how to design the harvester. In this paper, a fixed volume of piezoelectric material is considered, and various design parameters are discussed in order to achieve an improved design. The main objective is to enhance the harvester performance, considering electrical and mechanical aspects, simultaneously. The output power, the level of induced stress on the piezoelectric material, the endurance limit, and the coupling effect of the device with the pavement are considered. As a case study, the finite element model of a piezoelectric harvester is developed and validated with the experimental results. A parametric study is then carried out in order to improve both the electrical and mechanical characteristics of the device. Various parameters, such as piezoelectric disks cross-section, piezoelectric material, as well as the disks aspect ratio are considered. The proposed structures are compared with similar ones reported in the literature and show higher output powers of 3 − 5.8 times. A case study is presented to show the signal conditioning process of the harvested power for practical applications. Improvements in various aspects of the device performance, while considering the economic aspects, i.e., the amount of consumed piezoelectric material, show the effectiveness of the proposed method.

    更新日期:2020-01-08
  • Aero-engine blade profile reconstruction based on adaptive step size bat algorithm and visualization of machining error
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-09-11
    Zhi Huang; Pengxuan Wei; Chao Li; Hongyan Wang; Jingyi Wang

    High-precision profile reconstruction is a key issue in the profile detection and visualization of aero-engine blades. A method based on adaptive step size bat algorithm (ASSBA) for blade profile reconstruction and an adaptive mesh model for visualization analysis of the key machining errors are proposed. Firstly, the original bat algorithm (BA) is improved to introduce the global stage and local search stage. Then, combined with the node layer characteristics of the blade measurement data, the ASSBA is used to fit the optimal surface. Further, the adaptive mesh is planned on the blade profile to extract various evaluation parameters. Finally, the algorithm analysis and verification are carried out based on a certain type of blade. The results show this reconstruction method can get the fitted surface more quickly and accurately than other iterative methods. Simultaneously, the visualization method and corresponding software system can intuitively visualize the blade profile error, the twist deformation error, the swept deformation error, the bending deformation error and the cross-section line profile error.

    更新日期:2020-01-08
  • Process optimization for rapid manufacturing of complex geometry electrical discharge machining electrode
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-09-12
    Jagtar Singh; Pulak M Pandey

    Rapid manufacturing techniques permit tools and dies to be fabricated in short duration of time with complex geometry. The major contribution of the present research was to fabricate copper complex geometry electric discharge machining electrode by using amalgamation of three-dimensional printing along with pressureless loose sintering. Response surface methodology was employed to study the sintering parameters’ (sintering temperature, heating rate and soaking time) effect on electric discharge machining electrode important characteristics such as density, shrinkage and electrical conductivity. Analysis of variance was used to investigate the significant contribution of the parameters on the responses. Density and electrical conductivity of fabricated electric discharge machining electrode were revealed to increase with respect to rise in soaking time and sintering temperature. The interaction between the heating rate and sintering temperature for density and electrical conductivity responses signified the less effect of heating rate at high temperatures. Further, multi-objective optimization was used to maximize density and electrical conductivity and to minimize volumetric shrinkage. Different shapes of electric discharge machining electrodes were fabricated at optimized parameters. In addition, the fabricated electrodes were tested on electric discharge machining of D2 steel for 5 mm depth. The dimensional analysis was carried out between the computer aided design (CAD) model, fabricated electric discharge machining electrode and the obtained cavity by electric discharge machining process. The results depicted high efficacy of the process to fabricate complex geometry electric discharge machining electrodes.

    更新日期:2020-01-08
  • Experimental investigations into mechanical and thermal properties of rapid manufactured copper parts
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-09-17
    Gurminder Singh; Pulak M Pandey

    In the present paper, mechanical and thermal properties of rapidly manufactured copper parts were studied. The combination of three-dimensional printing and ultrasonic assisted pressureless sintering was used to fabricate copper parts. First, the ultimate tensile strength and thermal conductivity were compared between ultrasonic assisted and conventional pressureless sintered samples. The homogenously mixing of particles and local heat generation by ultrasonic vibrations promoted the sintering driving process and resulted in better mechanical and thermal properties. Furthermore, response surface methodology was adopted for the comprehensive study of the ultrasonic sintering parameters (sintering temperature, heating rate, and soaking time with ultrasonic vibrations) on ultimate tensile strength and thermal conductivity of the fabricated sample. Analysis of variance was performed to identify the significant factors and interactions. The image processing method was used to identify the surface porosity at different parameter levels to analyse the experimental results. High ultimate tensile strength was obtained at high sintering temperature, long soaking time, and slow heating rate with low surface porosity. After 60 min of soaking time, no significant effect was observed on the thermal conductivity of the fabricated sample. The significant interactions revealed less effect of soaking time at low sintering temperatures for ultimate tensile strength and less effect of heating rate at low sintering temperatures for thermal conductivity. Multi-objective optimization was carried out to identify parameters for maximum ultimate tensile strength and maximum thermal conductivity.

    更新日期:2020-01-08
  • Dynamic load identification algorithm based on Newmark-β and self-filtering
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-09-12
    Fan Yuchuan; Chunyu Zhao; Yu Hongye; Bangchun Wen

    In this paper, a dynamic load identification iteration algorithm based on Newmark-β is proposed. Aiming at the problem of excessive iteration error in the process of calculation, a self-filtering algorithm is proposed and added to the load identification algorithm. After adding the self-filtering algorithm, the recognition accuracy of the algorithm has been improved significantly. The recognition result of the proposed method and explicit Newmark-β method is compared by simulations and experiment. The results show that the recognition precision and calculation efficiency of this algorithm are higher, especially in the aspect of calculation efficiency, the proposed method has obvious advantages. Under the same conditions, the proposed method can save a lot of computation time.

    更新日期:2020-01-08
  • Force characteristics and two-dimensional pressure fields of air flotation units with different numbers and distribution radii of orifices
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-09-17
    Xubo Yu; Chengye Zou; Kaige Shi; Xin Li

    Air flotation rails are widely used in semiconductor production lines for handling components such as liquid crystal glass substrates and wafers. In this study, the effects of the number and distribution radius of the orifices of the basic component (hereinafter referred to as air flotation unit) of the utilized air-suspension orbit were theoretically and experimentally investigated. The pressure distribution of the air flotation unit was first calculated using the Reynolds equation. The flotation forces and two-dimensional pressure fields of six different air flotation units with different numbers and distribution radii of the orifices were then experimentally measured. Based on the experimental data, we analyzed the effect of the inertia item of the flow, the impact of the no-flow region within the distribution circle, and the changes brought about by the number and distribution radius of orifice, etc. The findings of this study afford important theoretical and experimental references for the design of air flotation rails.

    更新日期:2020-01-08
  • Complete kinematic calibration of a 6-RRRPRR parallel kinematic machine based on the optimal measurement configurations
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-09-02
    Chunyang Han; Yang Yu; Zhenbang Xu; Xiaoming Wang; Peng Yu; Xiaoqin Zhou

    This paper presents a kinematic calibration of a 6-RRRPRR parallel kinematic mechanism with offset RR-joints that would be applied in space positioning field. In order to ensure highly accurate and highly effective calibration process, the complete error model, which contains offset universal joint errors, is established by differentiating inverse kinematic model. A calibration simulation comparison with non-complete error model shows that offset universal joint errors are crucial to improve the calibration accuracy. Using the error model, an optimal calibration configuration selection algorithm is developed to determine the least number of measurement configurations as well as the optimal selection of these configurations from the feasible configuration set. To verify the effectiveness of kinematic calibration, a simulation and experiment were performed. The results show that the developed approach can effectively improve accuracy of a parallel kinematic mechanism with relatively low number of calibration configurations.

    更新日期:2020-01-08
  • Design guidelines for the striker and transfer flange of a split Hopkinson tension bar and the origin of spurious waves
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-08-31
    Hyunho Shin; Jae-Ha Lee; Jong-Bong Kim; Sung-Ik Sohn

    Characteristics of the stress pulse generated by impact of a hollow striker on the flange of a split Hopkinson tension bar are investigated via an explicit finite element analysis. Design guidelines are extracted for the hollow striker and flange from the viewpoint of eliminating spurious waves located between the incident and reflected pulses. According to design guidelines, it is desirable to have a striker cross-sectional area the same as that of the flange. It is also desirable to make the cross-sectional area of the striker (flange) the same as that of the bar. As for the flange length, it is recommended to be comparable to the diameter of the bar. The magnitude and duration of the primary stress pulse are consistent with the results of a one-dimensional analysis even when spurious waves are present; meanwhile, overly long spurious waves should be avoided to eliminate their superposition with the reflected pulse. Spurious waves appear when general impedance of the striker is higher than the bar. The origin of spurious waves is a series of step-wise residual pulses generated by multiple cycles of striker impact that make the striker keep compressing the flange after the first cycle of impact. Step-wise residual pulses appear in two forms (continuous waves and discrete waves) in spurious waves due to the secondary impacts during the entrance process of step-wise residual pulses to the flange. The consequences of spurious waves in the use of split Hopkinson tension bars are discussed.

    更新日期:2020-01-08
  • Investigation of the scattering of Lamb waves from a generalized circular cavity by using Poisson/Mindlin plate theories and numerical simulation
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-08-28
    Adel Sedaghati; Farhang Honarvar; Morteza Tabatabaeipour; Anthony N Sinclair

    A mathematical model for the scattering of a symmetric S0 Lamb wave mode from a circular cavity in an isotropic plate is developed that can handle both symmetric and asymmetric single- and double-sided blind holes. The theoretical formulation is based on Mindlin and Poisson plate theories. A finite element model is also utilized to extract the scattering patterns of Lamb waves from various cases of a generalized circular cavity. Two-dimensional FFT analysis is used to determine the transmitted and reflected Lamb wave modes when the incident wave interacts with either symmetric (through-hole and double-sided blind hole) or asymmetric (blind hole and double-sided blind hole) cavities. Results indicate that the remaining thickness of a cavity zone and the type of a cavity are two key parameters in the scattering pattern. For asymmetric cavities, the shape of the scattering pattern of the mode-converted A0 mode does not vary significantly. However, the amplitude of the scattering pattern shows noticeable changes in the out-of-plane component of the displacement. Results obtained from the proposed theory and finite element model are in good agreement with previously published data.

    更新日期:2020-01-08
  • Microstructural evolution and mechanical behaviors of equal channel angular pressed copper
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-08-31
    Reza Pourhamid; Ali Shirazi

    The mechanical properties including Vickers hardness, tensile properties, fracture toughness, impact toughness and also, the microstructure of copper severely deformed by equal channel angular pressing through route C after two, four, and eight passes at ambient temperature, were studied in the present work. The results indicated that the grains size reduced from 16.7 to 4.8 µm after two and to 2.1 µm after eight passes. This study cleared that because of the recrystallization phenomenon and reducing the effect of stress concentration and increasing the number of grain boundaries, the values of the fracture toughness can increase significantly. For example, fracture toughness increases by 58.4% relative to base metal after eight passes equal channel angular pressing. Also, it was found that the major improvement in tensile properties is achieved after two passes and due to the applied simple shear to the copper, all the equal channel angular pressed specimens have demonstrated an enhanced hardness and impact toughness, in accordance with their number of equal channel angular pressing passes. For example, the Vickers hardness is increased by a factor of 1.98 and impact toughness 58.4% for the extruded material after eight passes.

    更新日期:2020-01-08
  • Dynamic behavior of particulate metal matrix nanocomposite plates under low velocity impact
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-09-17
    M Rasoolpoor; R Ansari; MK Hassanzadeh-Aghdam

    The main purpose of this work is to investigate low velocity impact behavior of metal matrix nanocomposite plates reinforced with silicon carbide nanoscale particles. First, a micromechanical model is proposed to predict the effective mechanical properties of metal matrix nanocomposites. Two features of the nanocomposite microstructure affecting the elastic properties, including agglomerated state of silicon carbide nanoparticles and size factor, are taken into account in the micromechanical simulation. Then, finite element method is used to analyze the time histories of contact force and center deflection of silicon carbide nanoparticle-reinforced metal matrix nanocomposite plates. Several detailed parametric studies are accomplished to explore the influence of volume fraction, diameter and dispersion type of silicon carbide nanoparticles, spherical impactor velocity and diameter, plate dimensions, as well as different boundary conditions on the dynamic response of metal matrix nanocomposite plates. The presented approach accuracy is verified with the available open literature results displaying a clear agreement. The results indicate that adding the silicon carbide nanoparticles into the metal matrix materials leads to a reduction in plate center deflection and an increase in contact force between the plate and projectile. Moreover, it is found that the nanoparticle agglomeration dramatically decreases the contact force and increases the center deflection of metal matrix nanocomposite plates.

    更新日期:2020-01-08
  • Numerical analysis of different cutting edge radii in hot micro-cutting of Inconel 718
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-09-17
    Xin Liu; Xu Zhang; Dazhong Wang

    Mechanical micro-cutting is one of the advanced processes for manufacturing of micro-parts. During the micro-cutting process, the thickness of the uncut chip is very close to the tip radius of the tool. The cutting edge is used to cut and extrude the workpiece. In this paper, the experiments and simulations of macro-machining nickel alloy are compared, and the process of micro-cutting nickel alloy is simulated and analyzed. In this study, four cutting edge radii, three cutting speeds, six hot cutting temperatures, and a constant depth of cut are used. The radius of the cutting edge of different sizes is theoretically analyzed and verified by simulation of material flow state, temperature, stress, strain, and cutting force. The results show that the material separation points are very close together at different cutting edge radii. The change in the radius of the cutting edge changed the contact state of the material in the cutting area, which has a large influence on the temperature and cutting force. The effects of different cutting speeds and hot working temperature on the machining process are also discussed.

    更新日期:2020-01-08
  • A novel multiple working modes parallel mechanism with variable workspace
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2018-10-25
    Dian Li; Sheng Guo; Haibo Qu

    In this paper, a novel three-degrees-of-freedom multiple working modes parallel mechanism with variable workspace is proposed. Several studies including kinematic and prescribed trajectory planning are performed. First, the degrees of freedom of mechanism's two working modes are calculated based on screw theory. A prototype made by 3D printer also has been developed. Then, the inverse/forward kinematics and Jacobian matrices are obtained. The workspace and singularity are also analyzed, which show that the proposed parallel mechanism possesses singularity-free internal workspace. Finally, a working mode determination method is presented, which can be used to obtain suitable workspace in order to fully contain a prescribed trajectory. An example trajectory is used to verify the reasonability of the proposed method.

    更新日期:2020-01-08
  • Kinematic analysis of a PPPR spatial serial mechanism with geometric errors
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2018-11-04
    Xingxing Feng; Haihua Sun; Tianqi Lv; Yunqing Zhang

    The present study focuses on the kinematic analysis of a PPPR spatial serial mechanism with a large number of geometric errors. The study is implemented in three steps: (1) development of a map between the end-effector position error and geometric source errors within the serial mechanism kinematic chains using homogeneous transformation matrix; (2) selection of geometric errors which have significant effects on end-effector positioning accuracy by sensitivity analysis; (3) kinematic analysis of the serial mechanism within which the geometric errors are modelled as interval variables. The computational algorithms are presented for positioning accuracy analysis and workspace analysis in consideration of geometric errors. The analysis results show that the key factors which have significant effects on end-effector position error can be identified efficiently, and the uncertain workspace can also be calculated efficiently.

    更新日期:2020-01-08
  • A Sarrus-like overconstrained eight-bar linkage and its associated Fulleroid-like platonic deployable mechanisms
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2018-12-10
    Haohua Xiu; Kunyang Wang; Guowu Wei; Lei Ren; Jian S Dai

    This paper, for the first time, presents an overconstrained spatial eight-bar linkage and its application to the synthesis of a group of Fulleroid-like deployable platonic mechanisms. Structure of the proposed eight-bar linkage is introduced, and constrain and mobility of the linkage are revealed based on screw theory. Then by integrating the proposed eight-bar linkage into platonic polyhedron bases, synthesis of a group of Fulleroid-like deployable platonic mechanism is carried out; which is demonstrated by the synthesis and construction of a Fulleroid-like deployable tetrahedral mechanism. Further, mobility of the Fulleroid-like deployable platonic mechanisms is formulated via constraint matrices by following Kirchhoff’s circulation law for mechanical networks, and kinematics of the mechanisms is presented with numerical simulations illustrating the intrinsic kinematic properties of the group of Fulleroid-like deployable platonic mechanisms. In addition, a prototype of the Fulleroid-like deployable spherical-shape hexahedral mechanism is fabricated and tested; verifying the mobility and kinematic characteristics of the proposed deployable polyhedral mechanisms. Finally, application of the proposed deployable platonic mechanisms is demonstrated in the development of a transformable quadrotor. This paper hence presents a novel overconstrained spatial eight-bar linkage and a new geometrically intuitive method for synthesising Fulleroid-like regular deployable polyhedral mechanisms that have great potential applications in deployable, reconfigurable and multifunctional robots.

    更新日期:2020-01-08
  • Kinematic analysis of deployable parallel mechanisms
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-02-02
    Shuofei Yang; Yangmin Li

    Inspired by the existing closed-loop deployable mechanisms and parallel mechanisms, a new kind of mechanisms, named deployable parallel mechanisms, is introduced in this paper, and the kinematic analysis is presented. As the combination of deployable mechanisms and parallel mechanisms, deployable parallel mechanisms have advantages of both the two kinds of mechanisms. They can be easily constructed by origami and folded from spatial structures into paper slices. Due to the parallel structures, they can be designed to have higher stiffness and larger volume compressibility than the existing deployable mechanisms. Thus, deployable parallel mechanisms have tremendous potential to be applied in the design of spatial solar panels, elastic reconfigurable robotic modules, etc. With reference to the kinematic analysis of parallel mechanisms, a finite and instantaneous screw method for kinematics of deployable parallel mechanisms is proposed, which is a generic method that is suitable for displacement and velocity modeling and analysis of any deployable parallel mechanism. A typical mechanism with symmetrical structure is taken as an example to show the validity of the proposed method, and simulation and experiment are carried out to verify the obtained results of kinematics. This paper puts forth the basic concepts of deployable parallel mechanisms and lays a theoretical foundation for their kinematic modeling and analysis.

    更新日期:2020-01-08
  • Novel approach for planetary gear train dimensional synthesis through kinematic mapping
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-02-26
    Liang Sun; Zhenfei Wang; Chuanyu Wu; Guofeng Zhang

    The synthesis of a kinematic trajectory traversed by an output link (planet gear) and posture of a planetary gear train with noncircular gears can be divided into two phases: dimensional synthesis of the open-chain 2R mechanism (planetary carrier) and optimization of the transmission ratio of noncircular gear pairs. According to kinematic mapping theory, more than one closed coupler trajectory can be obtained by five preset poses. Simultaneous consideration of the trajectory shape, posture, and gear ratio is difficult during planetary gear train synthesis. This work therefore proposes a new method for the synthesis of planetary gear train in which different path segments in different trajectories are selected and a group of same-type 2R mechanisms is employed to pass through them in order to rebuild a new, closed trajectory. Subsequently, the transmission ratio of noncircular gear pairs can be determined using the relative angular displacement of the 2R mechanism. To improve the roundness of the pitch curves of noncircular gears, two optimization steps are implemented using a genetic algorithm without alternating the data points of the requisite open trajectories. For example, a mechanism for rice pot seedling transplanting is obtained by using the method.

    更新日期:2020-01-08
  • Assessing worker performance using dynamic cost functions in human robot collaborative tasks
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-03-26
    Thomas Smith; Panorios Benardos; David Branson

    The aim of this research is to develop a framework to allow efficient human robot collaboration on manufacturing assembly tasks based on cost functions that quantify capabilities and performance of each element in a system and enable their efficient evaluation. A proposed cost function format is developed along with initial development of two example cost function variables, completion time and fatigue, obtained as each worker is completing assembly tasks. The cost function format and example variables were tested with two example tasks utilizing an ABB YuMi Robot in addition to a simulated human worker under various levels of fatigue. The total costs produced clearly identified the best worker to complete each task with these costs also clearly indicating when a human worker is fatigued to a greater or lesser degree than expected.

    更新日期:2020-01-08
  • Analysis and experiments on a novel smoothly moving low-DoF multilegged robot
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-05-12
    Qiang Ruan; Yan-an Yao; Jian-xu Wu

    SmooBot, a novel low-degree-of-freedom multilegged robot with a smoothly moving platform is proposed in the paper, which is aimed at helping people do the delivery jobs in the industrial site. Cam compensation mechanisms are applied to the robot so the platform keeps smoothly moving while the robot is walking. With the special design of the compensation mechanism, the height, velocity, and attitude of the platform almost keep constant. The motion input of the compensation mechanism shares the same continuous rotation with the mechanical legs and remain the compact structure. The cam mechanisms are designed based on the kinematics analysis of the mechanical legs. The walking simulations and prototype experiments are carried out to testify the theoretical analysis. Based on the simulation and experiment results, the enhancements of the compensation mechanisms in the platform smoothness and the energy efficiency are discussed. The study in the paper provides a new idea to enable a low-degree-of-freedom multilegged robot to have a smoothly moving platform and to carry heavy load at a high speed by using the cam compensation mechanisms.

    更新日期:2020-01-08
  • A hybrid continuum robot based on pneumatic muscles with embedded elastic rods
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-01-08
    Cijing Sun; Lisha Chen; Jinguo Liu; Jian S Dai; Rongjie Kang

    Continuum robots have attracted increasing attention in recent years due to their intrinsic compliance and safety. Nevertheless, the use of structure compliance may lead to reduction of stiffness and positioning precision. This paper presents a novel design of a hybrid continuum robot whose actuators are composed of pneumatic muscles and embedded elastic rods. Such robot can switch drive modes between large-scale movement and fine adjustment of position by employing a locking mechanism to change its stiffness. A three-dimensional static model of the robot is presented using an improved Kirchhoff rod theory, where elastic deformation of the robot is accounted for from an optimal control point of view via minimal total potential energy principle. Experiments were carried out to validate the static model and to test the stiffness and precision of the robot. This work provides a possible way to strengthen the control precision of a continuum robot with compliant structure.

    更新日期:2020-01-08
  • Tool wear prediction in hard turning of EN8 steel using cutting force and surface roughness with artificial neural network
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-09-09
    Thangarasu SK; S Shankar; Mohanraj T; Devendran K

    In this work, the flank wear of the cutting tool is predicted using artificial neural network based on the responses of cutting force and surface roughness. EN8 steel is chosen as a work piece material and turning test is conducted with various levels of speed, feed and depth of cut. Cutting force and surface roughness are measured for both the fresh and dull tool under dry cutting conditions. The tool insert used is CNMG 120408 grade, TiN coated cemented carbide tool. The experiments are conducted based on the response surface methodology face central composite design of experiments. The feed rate (14.52%), depth of cut (27.72%) and the interaction of feed rate and depth of cut (50.39%) influence the cutting force. The feed rate (21.33%) and the interaction of cutting speed and depth of cut (26.67%) influence the flank wear. The feed rate (61.63%) has the significant influence on surface roughness. The feed forward back propagation neural network of 5-n-1 architecture is trained using the algorithms like Levenberg Marquardt, BFGS quasi-Newton, and Gradient Descent with Momentum and Gradient descent with adaptive learning rate. The network performance has been assessed based on their mean square error and computation time. From this analysis, the BFGS quasi-Newton back propagation algorithm produced the least mean squared error value with minimum computation time.

    更新日期:2020-01-08
  • Raw vibration signal pattern recognition with automatic hyper-parameter-optimized convolutional neural network for bearing fault diagnosis
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-09-19
    Heng Li; Qing Zhang; Xianrong Qin; Sun Yuantao

    Bearing fault diagnosis is of great significance for evaluating the reliability of machines because bearings are the critical components in rotating machinery and are prone to failure. Because of non-stationarity and the low signal-noise rate of raw vibration signals, traditional fault diagnosis methods often construct representative fault features via the technologies of feature engineering. These methods rely heavily on expertise and are inadequate in actual applications. Recently, methods based on convolutional neural networks have been studied extensively to relieve the demands of hand-crafted feature extraction and feature selection. However, the raw vibration signal is rarely taken as a direct input. This study combines a convolutional neural network with automatic hyper-parametric optimization and proposes two deep learning models for time-series pattern recognition to achieve “end-to-end” bearing fault diagnosis: a one-dimensional-convolutional neural network and a dilated convolutional neural network. The architecture of the two models are tweaked by automatic optimization rather than manual trial or grid search. Further, we try to figure out the inner operating mechanism of the proposed methods by visualizing the automatically learned features. The proposed methods are applied to diagnose roller bearing faults on a benchmark experiment and a prototype experiment. The results verify that our methods can achieve better performance than other intelligent methods via a Gaussian-noise test.

    更新日期:2020-01-08
  • Coating effect on the fatigue strength of a free cutting steel
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-03-18
    Dario Croccolo; Massimiliano De Agostinis; Stefano Fini; Giorgio Olmi; Francesco Robusto

    Free cutting steels, which are commonly used in many mass production fields, such as the automotive industry and household appliances, contain sulfur, lead, and some other elements, which promote machinability. For this reason, this class of materials is widely used in lock industries, which are characterized by very large production batches in order to cut production costs. It must be observed that, in some cases, free-cutting steel components must withstand remarkably high fatigue loads, even in harsh environment. For example, as indicated by Standard,1 the lock shall be mounted in a fixture being similar to a door application. Afterwards, it is sprayed by neutral salt for a defined duration: in this particular condition, it is required to comply with some standard requirements and to pass specific tests to ensure its ability to operate after environmental exposure. To achieve acceptable material properties, thus improving wear resistance, even in harsh environments, considering as well cost issues, the widespread procedure in the lock industries is to use electrodeposited coatings over free-cutting steel materials. This is a very serious issue, as the failure of the locking devices may arise both from too high wear, which is no longer compliant with the standard requirement, and from fatigue damage. In particular, some authors indicate that coatings may have a detrimental effect on the fatigue strength of the materials.2–6 Therefore, it is important to clarify this point, depending on the involved materials and coatings, and, in case, to search a compromise. For these reasons, some free-cutting steels have been investigated in the last years.7–13 However, a literature survey still indicates a lack of knowledge in this field, in particular regarding the interaction between the material properties and the coating alloy components and the related combined effect on the mechanical response with particular reference to fatigue.

    更新日期:2020-01-06
  • Artificial neural network for Gaussian and non-Gaussian random fatigue loading analysis
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-10-01
    JF Durodola

    Stationary ergodic Gaussian random data have been the convenient basis of many of the data used for the development of models for the analysis of random vibration fatigue problems especially using spectral-based methods.1–5 It is, however, known that non-Gaussian excitations occur due to road irregularities in automobiles and turbulent pressure flections in the aerospace sector.6,7 Highly non-Gaussian excitations occur on rail vehicles caused by wheel–rail contact.8 Wind loading effects are also known to be non-Gaussian with high uncertainties and peak values.9 The main consequence of non-Gaussian data effect is that its peakedness effect can be overlooked in analysis and may lead to failure. There have, therefore, been a lot of interest in non-Gaussian fatigue loading analysis.7,10 A number of researchers have attempted to use higher order statistical properties such as signal Kurtosis as an additional parameter to resolve issues associated with inaccuracies encountered in fatigue life prediction under non-Gaussian loading condition.11 A lot of effort has also been going on towards the modelling simulation of non-Gaussian data for fatigue analysis.7,10,12,13

    更新日期:2020-01-06
  • A pseudo-modal structural damage index based on orthogonal empirical mode decomposition
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-11-07
    Egidio Lofrano; Francesco Romeo; Achille Paolone

    Damage identification attracts wide attention and in-depth research in numerous engineering fields for its paramount importance for systems safety and operational assessment. Among the proposed techniques, structural vibration-based ones are increasingly considered. There are two main reasons behind this progression: a practical motivation, related to the aptitude of dynamic tests in capturing the real behaviour of structural systems,1,2 and a technological reason, related to the reduction of costs and the miniaturisation of the electronic acquisition devices.3 Vibration-based structural health monitoring systems are nowadays widespread, for both new and existing structural systems, and dynamic structural damage identification is a new target of a wide scientific community.4 However, this task is intrinsically more complicated than the ‘mere’ structural identification one, since it calls for extracting damage-sensitive features over time from periodically spaced response measurements. Mathematical models derived from physical basis are used for modelling mechanical systems, often resorting to output-only modal parameter estimation methods5,6; alternatively, data-driven models describing the systems input–output relation are adopted. A trade-off between the two approaches is based on the combination of both, physical insights and experimental data. As reported in the comprehensive reviews published in the last two decades,7–9 the variety of proposed identification strategies are devised to detect, localise, quantify damage and, ultimately, to estimate the remaining service life of the structure. These goals are pursued by relying on different quantities, i.e. physical properties (mass, stiffness, damping), modal properties (natural frequencies, mode shapes, modal damping) and structural response signal features (e.g. Fourier, Wavelet or Hilbert transform). In essence, all the identification strategies aim at extracting reliable signs for early diagnosis of structural damage from the least amount of data. For most real structural systems, direct measurement of global physical properties and their variations, possibly ascribable to damage, is unfeasible; therefore, local, albeit numerous, dynamic response quantities are usually relied upon. Modal property-based approaches seek after dynamic response alteration due to damage, which is usually expected to cause a change in stiffness. Predictive models and physically sound interpretations can be provided by these approaches. However, some difficulties may arise, such as the need to rely on accurate structural modelling and to select proper response signals, not to mention the lack of solution uniqueness of the inverse problem. Differently, signal processing-based techniques seek after signals changes, in time and frequency, between undamaged and damaged states. Direct evidence of signals alteration can be readily detected; however, its physical interpretation is often cumbersome.

    更新日期:2020-01-06
  • Nondestructive monitoring of damage caused by accelerated ageing in photovoltaic modules
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-11-28
    Irene Berardone; Marco Paggi

    Due to outdoor exposure, photovoltaic (PV) modules are subjected to degradation phenomena during their expected lifetime (20–25 years). Producer warranties claim power losses lower than 10% of the initial nominal power during the first 10–12 years, and up to 20% after 20–25 years of operation, with different power loss rates.1 Many external sources of stress, like solar radiation, wind, high temperature excursions, moisture, hail impacts, vibrations, fatigue, etc. contribute to PV damage.1–7 PV degradation manifests itself as a gradual deterioration of materials and components, affecting the optimal working conditions.8,9 As a result of that, electrical performances might decrease over time. In addition to this, safety issues are also related to material and component degradation. Conventionally, a relevant degradation occurs when the PV power output drops below 80% of its initial value,2 while the excess of degradation over a threshold specified for each failure mode could be critical for PV operation.10

    更新日期:2020-01-06
  • Recent advances and test processes in automotive and motorsports aerodynamic development
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-09-17
    V Senft; MA Gillan

    Aerodynamic development and testing have become fundamental to successful motorsport and road vehicle programs. The aerodynamic development of the vehicle is fully integrated within the complete design cycle. A mix of development techniques are used throughout the process, where the exact selection of the development tool depends on many factors ranging from performance to accessibility and economics. For example, the wind tunnel provides efficient and fast results of the full vehicle design concept. Computational fluid dynamics (CFD) provides insightful iterations and optimizations of vehicle sub-systems, and provides visual cues that resonate well with production car stylists. However, recent advances bring more capabilities to each of the tools, and provide aerodynamicists with enhanced options to optimize aerodynamic performance parameters. For example, advancements in robotic particle image velocimetry (PIV) and pressure probe measurements provide detailed flow field visualizations. Advancements in computational power and algorithms allow for more advanced full vehicle analysis.

    更新日期:2020-01-06
  • A review of H-Darrieus wind turbine aerodynamic research
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-11-15
    Longhuan Du; Grant Ingram; Robert G Dominy

    As the world economy continues to grow, energy demand is likely to increase despite efforts to increase the efficiency of energy use. The urgent need to meet this increasing demand and to reduce greenhouse gas emissions is being met, at least in part, by the development of large-scale wind turbines, both onshore and offshore. Nevertheless, for some situations including urban centres and off-grid locations there is an argument for the development of local, decentralized production of electric power to complement large-scale electric power plants which are located in just a few specific strategic locations. One of the most promising local production sources of clean electricity, for example in the built environment, is the small-scale wind turbine and, in particular, vertical axis machines that can tolerate large, rapid changes of wind direction. Although the small size of these turbines inevitably leads to a low power rating, in large numbers they can still contribute significantly to renewable energy production, improve building energy efficiency and make a considerable contribution to the future electricity generation mix.

    更新日期:2020-01-06
  • Recent trends and progress in the immersed boundary method
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-04-16
    Wei-Xi Huang; Fang-Bao Tian

    The immersed boundary method (IBM), first developed by Professor Peskin,1 is a methodology for dealing with boundary conditions at interfaces (including fluid–fluid and fluid–solid ones) based on meshes that do not conform to the shapes of the immersed boundaries or interfaces. The advantages of the IBM are manifold: the mesh generation is very easy even for complicated geometries; mesh movement and mesh regeneration are avoided for flows involving moving boundaries and fluid–structure interactions (FSIs); it is easy to handle the cases where the topology of the computational domain changes; and thus the computational efficiency could be higher than that of the traditional body-conformal grid approaches for the cases involving complicated geometries and large boundary movement.2–6 Due to its simplicity in mesh processing, the IBM has been attracting growing attention in the recent years with effort in developing new features and promoting its applications.7–26

    更新日期:2020-01-06
  • Flow mechanisms in axial turbine rim sealing
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2018-06-20
    John W Chew; Feng Gao; Donato M Palermo

    For every complex problem there is a solution that is simple, neat and wrong. – H. L. Mencken

    更新日期:2020-01-06
  • Task space-based orientability analysis and optimization of a wire-driven continuum robot
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-11-28
    Cong Wang; Shineng Geng; David T Branson; Chenghao Yang; Jian S Dai; Rongjie Kang

    In recent years, continuum robots mimicking biological structures such as octopus tentacles and elephant trunks have gained increasing attention due to their unique structural advantages of inherent compliance and adaptability. This enables them to be suitable for operations in narrow, complex, and unconstructed environments such as detection, rescue, and medical fields.1

    更新日期:2020-01-06
  • Design of flying robots inspired by the evolution of avian flight
    Proc. Inst. Mech. Eng. C J. Mec. Eng. Sci. (IF 1.359) Pub Date : 2019-07-10
    Farzeen Shahid; Jing-Shan Zhao; Pascal Godefroit

    The origin and early evolution of birds and avian flight is one of the most discussed topics in palaeontology. Two years after Darwin’s celebrated book On the Origin of Species, one of the major clues for understanding the origin of birds was already discovered in Upper Jurassic limestones from Bavaria in Germany.1,2 The skeleton of Archaeopteryx is characterized by a mosaic of “reptilian” (teeth, claws, bony tail, unfused hand fingers) and avian (feathers, furcular, perching feet).3 Recent discoveries of hundreds of incredibly preserved specimens of feathered dinosaurs and early birds from Middle Jurassic to Early Cretaceous deposits in north eastern China definitely proved that birds are closely related to small carnivorous dinosaurs. Dinosaurs did not completely disappear 65 million years ago, as often depicted, but some of them, known as “birds”, survived and even flourished until today.

    更新日期:2020-01-06
Contents have been reproduced by permission of the publishers.
导出
全部期刊列表>>
2020新春特辑
限时免费阅读临床医学内容
ACS材料视界
科学报告最新纳米科学与技术研究
清华大学化学系段昊泓
自然科研论文编辑服务
中国科学院大学楚甲祥
上海纽约大学William Glover
中国科学院化学研究所
课题组网站
X-MOL
北京大学分子工程苏南研究院
华东师范大学分子机器及功能材料
中山大学化学工程与技术学院
试剂库存
天合科研
down
wechat
bug