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  • Dynamic response and validation of a flexible matrix composite
    J. Compos. Mater. (IF 1.755) Pub Date : 2019-04-25
    Daniel Whisler; Rafael G Consarnau; Ezequiel Buenrostro

    Testing and predicting the dynamic response of flexible matrix composites in impact loading condition face two primary challenges: (i) experimentally, existing techniques using existing instruments do not always provide high fidelity material data under simultaneous high strain and high strain rate loading conditions; and (ii) finite element simulations of a highly flexible material require many material parameters and complex mathematical formulations. To address these limitations, this research investigation presents a technique originally developed in-house for modeling and validating hyper-viscoelastic materials and applies it toward the flexible matrix composite. Results from a simple low-velocity impact (2 m/s) test on a 75 × 75 mm2 flexible matrix composite indicate that the critical material properties for the low strength, highly deformable matrix in conjunction with an updated constitutive model can accurately predict the dynamic behavior within 10% with respect to the force time history response using MATLAB and ABAQUS/Explicit. Finite element interrogation also shows full field stress response within the composite specimen not easily measured via sensors and deformation matching the behavior observed via high-speed camera. Finally, on-going research in this arena indicates that the technique can be applied to higher rate loading mechanisms, such as a gas gun and Hopkinson bar apparatus, in order to obtain material parameters for even more devastating impact loading strain rates.

  • A three-dimensional progressive damage model for drop-weight impact and compression after impact
    J. Compos. Mater. (IF 1.755) Pub Date : 2019-06-29
    Dinh Chi Pham; Jim Lua; Haotian Sun; Dianyun Zhang

    In this paper, an enhanced three-dimensional continuum damage mechanics model is applied to predict the drop-weight impact response and compression after impact failure of a fiber-reinforced polymer composite specimen. The three-dimensional progressive damage model incorporates a three-dimensional maximum stress criterion to predict the intra-ply damage initiation, followed by a fracture-energy-based smeared crack model to capture the post-peak softening behavior. Driven by the dominant through-the-thickness failure under impact loading, a three-dimensional continuum damage model is implemented for the three-dimensional solid element via its explicit material model for Abaqus (VUMAT) to capture the effect of three-dimensional stress state and the interaction of matrix cracking and delamination. Abaqus’ restart analysis capability is used to activate the compression after impact analysis using the final damage state from the dynamic impact analysis. Both the dynamic failure and the compression after impact are demonstrated via a suite of verification examples followed by the sensitivity analysis using distinct impact configurations. The predictive capability of the proposed three-dimensional damage model is first verified using a static open-hole tension test. Applications of the damage model are then demonstrated for simulations of the dynamic drop-weight tests and compression after impact tests. A comparative study on the developed method is performed using the results predicted from the open-source CompDam. A sensitivity study is also performed to demonstrate the impact energy-dependent failure mode. The proposed model has shown its advantages in performing a quick assessment of impact damage and its effects on the residual compressive strength.

  • Implementing deformation, damage, and failure in an orthotropic plastic material model
    J. Compos. Mater. (IF 1.755) Pub Date : 2019-07-26
    Loukham Shyamsunder; Bilal Khaled; Subramaniam D Rajan; Robert K Goldberg; Kelly S Carney; Paul DuBois; Gunther Blankenhorn

    Theoretical and implementation details of an orthotropic plasticity model are presented. The model is comprised of three sub-models dealing with elastic and inelastic deformations, damage, and failure. The input to the three sub-models involves tabulated data that can be obtained from laboratory and/or virtual testing. In this article, the focus is on the development of the failure sub-model and its links to the other components. Details of how the user-selected failure criterion is used, and what steps are implemented post-failure are presented. The well-known Puck failure criterion is used in the numerical examples. Three validation tests are used to illustrate the strengths and weaknesses of the failure sub-model—10°, 15°, and 30° off-axis tests, a stacked-ply test carried out at room temperature under quasi-static loading, and finally, a high-speed impact test. Results indicate that while the deformation and damage sub-models give reasonably accurate results, the failure predictions are a huge challenge especially for high-speed impact tests.

  • Modeling and simulation of carbon composite ballistic and blast behavior
    J. Compos. Mater. (IF 1.755) Pub Date : 2019-08-08
    Chian-Fong Yen; Bob Kaste; Charles Chih-Tsai Chen; Nelson Carey

    The design of the next generation of aeronautical vehicles is driven by the vastly increased cost of fuel and the resultant imperative for greater fuel efficiency. Carbon fiber composites have been used in aeronautical structures to lower weight due to their superior stiffness and strength-to-weight properties. However, carbon composite material behavior under dynamic ballistic impact and blast loading conditions is relatively unknown. For aviation safety consideration, a computational constitutive model has been used to characterize the progressive failure behavior of carbon laminated composite plates subjected to ballistic impact and blast loading conditions. Using a meso-mechanics approach, a laminated composite is represented by a collection of selected numbers of representative unidirectional layers with proper layup configurations. The damage progression in a unidirectional layer is assumed to be governed by the strain-rate-dependent layer progressive failure model using the continuum damage mechanics approach. The composite failure model has been successfully implemented within LS-DYNA® as a user-defined material subroutine. In this paper, the ballistic limit velocity (V50) was first established for a series of laminates by ballistic impact testing. Correlation of the predicted and measured V50 values has been conducted to validate the accuracy of the ballistic modeling approach for the selected carbon composite material. A series of close-in shock hole blast tests on carbon composite panels were then tested and simulated using the LS-DYNA® Arbitrary-Lagrangian-Eulerian (ALE) method integrated with the Army Research Laboratory (ARL) progressive failure composite model. The computational constitutive model has been validated to characterize the progressive failure behavior in carbon laminates subjected to close-in blast loading conditions with reasonable accuracy. The availability of this modeling tool will greatly facilitate the development of carbon composite structures with enhanced ballistic impact and blast survivability.

  • Rate effects on fiber–matrix interfacial transverse debonding behavior
    J. Compos. Mater. (IF 1.755) Pub Date : 2019-10-04
    Jou-Mei Chu; Benjamin Claus; Boon Him Lim; Daniel O’Brien; Tao Sun; Kamel Fezzaa; Wayne Chen

    The rate effect of fiber–matrix interfacial debonding behavior of SC-15 epoxy with S-2 glass and aramid fiber reinforcements was studied via in-situ visualization of the transverse debonding event. In this study, the debonding force history, debonding initiation, debonding crack velocity, and crack geometry were characterized using a quasi-static load frame and a modified tension Kolsky bar at loading velocities of 0.25 mm/s and 2.5 m/s. Cruciform-shaped specimens were used for interfacial transverse debonding between SC-15 epoxy matrix and two types of fiber reinforcements. The load history and high-speed images of the debonding event were simultaneously recorded. A major increase was observed for the average peak debonding force and a minor increase was observed for the average crack velocity with increasing loading velocity. The crack geometry of the cruciform specimens under both loading velocities was also tracked. Scanning electron microscopy of the recovered specimens revealed the debonding direction along the fiber–matrix interface through angled patterns on the failure surface.

  • Failure behavior of woven fiberglass composites under combined compressive and environmental loading
    J. Compos. Mater. (IF 1.755) Pub Date : 2019-10-09
    Ariana Paradiso; Isabella Mendoza; Amanda Bellafato; Leslie Lamberson

    The purpose of this study is to quantitatively characterize the compressive and damage behavior of a woven fiberglass composite under combined environmental loading. Cuboidal samples of a commercially available woven fiberglass epoxy resin composite, garolite G10, are examined under uniaxial compressive loading perpendicular to the plies at quasi-static (10−3 s−1) and dynamic (103 s−1) strain rates using a standard load frame and Kolsky (split-Hopkinson) bar. In order to simulate environmental conditions, a subset of samples were soaked in either distilled or ASTM standard seawater prior to loading. Two time periods of environmental conditioning were investigated: short term at two weeks and long term at four months. Results demonstrate that, on average, the dynamic compressive strength of the fiberglass increased 35% from the quasi-static. Moreover, environmentally treated samples generally experienced a decrease strain to failure, and composites exposed to water for only short periods exhibited signs of the absorbed water sustaining additional load under quasi-static rates. Ultra-high-speed photography combined with digital image correlation, a full-field surface kinematic measurement technique, is used to map 2D strains on the sample during loading. In all cases, a clear shear failure mechanism from local instabilities appears, and a Mohr–Coulomb failure criterion is used to extract a mesoscale cohesive shear stress and coefficient of internal friction.

  • Dynamic impact behavior of syntactic foam core sandwich composites
    J. Compos. Mater. (IF 1.755) Pub Date : 2019-11-10
    P Breunig; V Damodaran; K Shahapurkar; S Waddar; M Doddamani; P Jeyaraj; P Prabhakar

    Sandwich composites and syntactic foams independently have been used in many engineering applications. However, there has been minimal effort towards taking advantage of the weight saving ability of syntactic foams in the cores of sandwich composites, especially with respect to the impact response of structures. To that end, the goal of this study is to investigate the mechanical response and damage mechanisms associated with syntactic foam core sandwich composites subjected to dynamic impact loading. In particular, this study investigates the influence of varying cenosphere volume fraction in syntactic foam core sandwich composites subjected to varying dynamic impact loading and further elucidates the extent and diversity of corresponding damage mechanisms. The syntactic foam cores are first fabricated using epoxy resin as the matrix and cenospheres as the reinforcement with four cenosphere volume fractions of 0% (pure epoxy), 20%, 40%, and 60%. The sandwich composite panels are then manufactured using the vacuum assisted resin transfer molding process with carbon fiber/vinyl ester facesheets. Dynamic impact tests are performed on the sandwich composite specimens at two energy levels of 80 J and 160 J, upon which the data are post-processed to gain a quantitative understanding of the impact response and damage mechanisms incurred by the specimens. A qualitative understanding is obtained through micro-computed tomography scanning of the impacted specimens. In addition, a finite element model is developed to investigate the causes for different damage mechanisms observed in specimens with different volume fractions.

  • Shadowed delamination area estimation in ultrasonic C-scans of impacted composites validated by X-ray CT
    J. Compos. Mater. (IF 1.755) Pub Date : 2019-07-27
    Andrew Ellison; Hyonny Kim

    Although ultrasonic pulse-echo C-scanning is a mature non-destructive evaluation technique for imaging internal damage in composite structures, a major impediment of obtaining a full characterization of the internal damage state is delamination shadowing effects. Specifically, shadowing refers to regions of interest that are behind other delamination planes or discontinuities with respect to the scanning surface. The delamination planes block ultrasonic wave transmission and the regions of interest are thus hidden (i.e. shadowed) from the scan. A methodology has been developed to expand ultrasonic scan data of impacted composites by utilizing damage morphology information that is well established in the composite impact research community, such as matrix cracks bounding delaminations, to estimate shadowed delamination information and matrix cracking. First, impacted flat composite plates were C-scanned by pulse-echo ultrasonic and the results were segmented by depth of damage to establish interface-by-interface delamination information. These delaminations were then fit by bounding lines representing the fiber/matrix crack directions defined by the orientations of plies adjacent to each interface to estimate the shadowed portion of the delamination results. The area inside this boundary was added to the original ultrasonic delamination area to create an estimation of the full delamination state at each shadowed interface. Additionally, because this extension method is based on the interactions between delaminations and matrix cracking, this extension method provides an approximation of the matrix cracking of adjacent plies. Results were compared with X-ray computed tomography scans to assess the effectiveness of the extension method.

  • Synthesis and characterization of Sr-doped HAp-incorporated polyether ether ketone composite
    J. Compos. Mater. (IF 1.755) Pub Date : 2019-11-18
    Anindya Pal; Bhabatosh Biswas; Ankita Das; Arindam Chakraborty; Pallab Datta; Amit Roy Chowdhury; Arijit Sinha

    Hydrothermally synthesized undoped and Sr-doped hydroxyapatite-dispersed polyether ether ketone composites has been fabricated by using hot isostatic pressing technique with 5, 10, 15, and 20 wt.% as the dispersoids content. The detailed structural investigation of the fabricated composites has been performed by scanning electron microscope, high-resolution transmission electron microscope, and X-ray diffraction technique that confirmed the uniform dispersion of the dispersoids with the polyether ether ketone matrix. The microindentation measurements show that the mechanical properties of the polyether ether ketone matrix improved remarkably with incorporation of the hydroxyapatite (HAp) particles. The nondestructively evaluated elastic modulus so obtained for the matrix and composites were further validated through finite element analysis. Moreover, the in vitro cytotoxic of the fabricated nanocomposites were also evaluated to assess its potential as a bioactive material.

  • Modeling the effect of uniaxial deformation on electrical conductivity for composite materials with extreme filler segregation
    J. Compos. Mater. (IF 1.755) Pub Date : 2019-07-10
    Oleg V Lebedev; Sergey G Abaimov; Alexander N Ozerin

    In this work, the correlation between electrical conductivity and uniaxial deformation of a material with highly segregated distribution of conductive filler is studied. Multi-walled carbon nanotubes are used as a model filler. A numerical model that can be used to predict changes in conductive microstructure made of multi-walled carbon nanotubes in response to uniaxial deformation of material is proposed. The model takes into account the ability of nanotubes to assume various conformations and orientations during deformation. Numerical simulations are conducted for uniformly distributed multi-walled carbon nanotubes providing confinement of the filler in a two-dimensional film structure with high volume fraction of the filler. The embedded element method to conduct realistic and computationally efficient simulation of multi-walled carbon nanotube behavior during deformation of the composite material is implemented. Finally, the results of numerical simulations of changes in electrical conductivity of composite during deformation are compared with the experimental data to prove the correctness of assumptions used in the model.

  • Short-beam shear of nanoprepreg/nanostitched three-dimensional carbon/epoxy multiwall carbon nanotube composites
    J. Compos. Mater. (IF 1.755) Pub Date : 2019-07-15
    Kadir Bilisik; Nesrin Karaduman; Erdal Sapanci

    The effect of out-of-plane stitching and the addition of multiwalled carbon nanotubes on the short-beam shear properties of carbon/epoxy composites were investigated. Stitching influenced the short-beam strength of carbon satin and twill fabric composites, where the stitched satin carbon/epoxy composites showed improved short-beam properties compared with the unstitched satin carbon/epoxy composites. In general, stitching and MWCNTs addition enhanced the short-beam strength of the composite. The fracture of the composites generally exhibited as a combination of lateral total matrix cracking, warp fiber breakage and interlayer opening. In addition, all the structures experienced angularly sheared catastrophic through-the-thickness layer breakage. It was also shown that delamination was largely restricted in stitched and nano-added composites when compared to the unstitched samples. It can be concluded that nanostitching could be considered for improving short-beam strength properties of the composite.

  • Effect of modified nano zinc oxide on physico-chemical and antimicrobial properties of gamma-irradiated sawdust/epoxy composites
    J. Compos. Mater. (IF 1.755) Pub Date : 2019-07-17
    Hoda A. Abdel-Rahman; Eman H. Awad; Rasha M. Fathy

    The present study aims to investigate the influence of modified zinc oxide nanoparticles content on the physico-chemical properties of sawdust/epoxy composite specimens. The results show an improvement in the mechanical properties in terms of flexural strength, impact strength, and hardness with increasing the modified zinc oxide nanoparticles content up to 5%, while the physical properties such as water absorption and thickness swelling percentages are decreased directly with increasing the content of modified zinc oxide. In addition, the behavior of irradiated composite specimens containing 5% modified zinc oxide nanoparticles at different gamma-irradiation doses, 10, 30, and 50 kGy, has been studied. The results indicate that the irradiated composite specimens at 10 kGy have better physico-chemical properties as compared to the unirradiated specimens. Furthermore, the antimicrobial properties of composite specimens containing 5% modified zinc oxide at 0 kGy and 10 kGy against different plant pathogenic fungi and bacteria are also discussed. The results demonstrate that the growth activity of fungi and bacteria on the composite specimens are reduced to a great extent as compared to the control composite specimens (0% of zinc oxide nanoparticles). Thermal behavior and morphology of the prepared specimens are detected using thermogravimetric analysis and scanning electron microscopy technique.

  • Nylon 612/TiO2 composites by anionic copolymerization-molding process: Comparative evaluation of thermal and mechanical performance
    J. Compos. Mater. (IF 1.755) Pub Date : 2019-07-17
    Elena Rusu

    This study describes the changes in some properties of two series of nylon 612/TiO2 composites by varying filler type (untreated and treated) and content (up 8.0 wt.%). The samples preparation by simultaneous anionic copolymerization-molding process ensures a good dispersion of the filler in matrix. Differential scanning calorimetry, thermogravimetrical analysis, static mechanical testing, dynamic mechanical analysis and scanning electron microscopy allowed to investigate the effects of filler loading on the mechanical, thermal and morphological characteristics of the samples and revealed the importance of filler treatment on the composites behaviour. The semicrystalline character has been proved by differential scanning calorimetry (only a single melting peak is present) and wide-angle X-ray diffraction (two reflexion plane with d-spacing of 0.4311 and 0.3817 nm appear). At the same filler content, the difference ΔHm1–ΔHc was higher for the samples with treated filler. The lower Tm,α(2) in comparison with Tm,α(1) revealed a modification of the nucleation process during crystallization. The main mass loss of the samples occurred between 277 and 550℃. The addition of the filler leads to the improvement of flexural strength and flexural modulus in comparison with neat copolymer. Incorporating 8.0 wt.% treated filler, the Tg value increases by about 11.0%, reaching 61.0℃.

  • Modeling and optimization of electrospinning conditions of PVB nanofiber by RSM and PSO-LSSVM models for improved interlaminar fracture toughness of laminated composites
    J. Compos. Mater. (IF 1.755) Pub Date : 2019-07-17
    Hossein Ipakchi; Amir Masoud Rezadoust; Masoud Esfandeh; Hamed Mirshekar

    In this study, the diameter of polyvinyl butyral nanofibers was modeled using response surface method based on three variables, at three levels of central composite design and particle swarm optimization-least squares support vector machine. Under optimal conditions, the measured mean diameter of the nanofibers was 175 nm. Sensitivity analysis in both models showed that polyvinyl butyral concentration in the solution was found to be the most effective parameter on the nanofiber diameter. The voltage is placed in the next. Fracture toughness under Mode I condition shows that the use of electrospun nanowebs as an interlayer in the structure of multi-layers composite has a positive effect on the GIc which values for the oriented and random nanofibers modified samples increased by 60% and 55%, respectively. According to SEM images, the main mechanism of fracture toughness in these samples was crack deflection and nanofibers crack bridging.

  • Fibre architecture modification to improve the tensile properties of flax-reinforced composites
    J. Compos. Mater. (IF 1.755) Pub Date : 2019-07-17
    Rishad Rayyaan; William Richard Kennon; Prasad Potluri; Mahmudul Akonda

    As far as the tensile properties of natural fibres as reinforcements for composites are concerned, flax fibres will stay at the top-end. However, an efficient conversion of fibre properties into their corresponding composite properties has been a challenge, due to the fibre damages through the conventional textile methods utilised to process flax. These techniques impart disadvantageous features onto fibres at both micro- and meso-scale level, which in turn degrade the mechanical performances of flax fibre-reinforced composites (FFRC). Undulation of fibre is one of those detrimental features, which occurs during traditional fibre extraction from plant and fabric manufacturing routes. The undulation or waviness causes micro-compressive defects or ‘kink-bands’ in elementary flax fibres, which significantly undermines the performances of FFRC. Manufacturing flax fabric with minimal undulation could diminish the micro-compressive defects up to a substantial extent. In this research, nonwoven flax tapes of highly aligned flax fibres, blended with a small proportion of polylactic acid have been manufactured deploying a novel technique. Composites reinforced from those nonwoven tapes have been compared with composites reinforced with woven Hopsack fabrics and warp knitted unidirectional fabrics from flax, comprising undulating fibres. The composites reinforced with the highly aligned tapes have shown 33% higher fibre-bundle strength, and 57% higher fibre-bundle stiffness in comparison with the composites reinforced with Hopsack fabric. The results have been discussed in the light of fibre undulation, elementary fibre individualisation, homogeneity of fibre distribution, extent of resin rich areas and impregnation of the fibre lumens.

  • Influence of filler loading on the mechanical and morphological properties of carbonized coconut shell particles reinforced polypropylene composites
    J. Compos. Mater. (IF 1.755) Pub Date : 2019-07-18
    Uchechi C Mark; Innocent C Madufor; Henry C Obasi; Udochukwu Mark

    The high cost of mineral-based fillers and their processing difficulties have necessitated the search for alternative and cheaper filler materials, usually agro-waste materials such as coconut shells. The coconut shells were carbonized, pulverized, and sieved into four particles sizes, namely; 63 μm, 150 μm, 300 μm, and 425 μm. The carbonized coconut shell particles of each particle size were used as fillers in the preparation of polypropylene-filled composites at filler loadings of 0, 10, 20, 30, and 40 wt. %. The control was the neat polypropylene of 0% filler addition. The polypropylene/carbonized coconut shell particles composites were prepared via melt blending of polypropylene and the filler in an injection molding machine to obtain composite sheets. The influence of filler loading on the mechanical properties was evaluated. The addition of fillers was found to improve the yield strength, tensile strength, tensile modulus, flexural strength, flexural modulus, and hardness of polypropylene as these mechanical properties increased with increase in filler loading. The elongation at break and modulus of resilience of the prepared polypropylene/carbonized coconut shell particles composites were, however, observed to decline with an increase in the filler loading. Compared with the neat polypropylene, the filler showed enhanced mechanical properties in the prepared composites. SEM revealed good filler–matrix interaction because of good interfacial adhesion. The incorporation of more filler resulted in the formation of more spherulite-producing nuclei, reduction of pore sizes, and enhanced particle size distribution with improved mechanical properties. Experimental data modeling showed the addition of more than 48% carbonized coconut shell particles to polypropylene would compromise property enhancement.

  • Analytical modeling and experimental validation of the low-velocity impact response of hemp and hemp/glass thermoset composites
    J. Compos. Mater. (IF 1.755) Pub Date : 2019-07-19
    Simonetta Boria; Carlo Santulli; Elena Raponi; Fabrizio Sarasini; Jacopo Tirillò

    Natural fiber composites have the potential to be widely applied as an alternative to or in combination with glass fiber composites in sustainable energy-absorbing structures. This study investigates the behavior of hemp fiber-reinforced vinylester composites when subjected to low-velocity impact loading by using an instrumented falling weight impact equipment. Different stacking sequences are tested, including a hybrid pattern resulting from a combination of natural and traditional glass fibers. Both penetration and indentation tests are performed. In the light of an increase in safety of green composite components and systems subjected to low-velocity impacts, next to the numerical models, the development of theoretical models is also useful and low time-consuming. Therefore, analytical models, available in the literature for traditional fiber-reinforced plastics and aimed at predicting the critical load of delamination onset, the indentation as a function of absorbed energy, as well as the approximation of the load–displacement curve, are used and implemented in this work. Good agreement was found between the theoretical predictions and experimental results.

  • Highly sensitive and stretchable strain sensors based on chopped carbon fibers sandwiched between silicone rubber layers for human motion detections
    J. Compos. Mater. (IF 1.755) Pub Date : 2019-07-15
    MB Azizkhani; Sh Rastgordani; A. Pourkamali Anaraki; J Kadkhodapour; B Shirkavand Hadavand

    Tuning the electromechanical performance in piezoresistive composite strain sensors is primarily attained through appropriately employing the materials system and the fabrication process. High sensitivity along with flexibility in the strain sensing devices needs to be met according to the application (e.g. human motion detection, health and sports monitoring). In this paper, a highly stretchable and sensitive strain sensor with a low-cost fabrication is proposed which is acquired by embedding the chopped carbon fibers sandwiched in between silicone rubber layers. The electrical and mechanical features of the sensor were characterized through stretch/release loading tests where a considerably high sensitivity (the gauge factor about 100) was observed with very low hysteresis. This implies high strain reversibility (i.e. full recovery in each cycle) over 700 loading cycles. Moreover, the sensors exhibited ultra-high stretchability (up to ∼300% elongation) in addition to a low stiffness meaning minimal mechanical effects induced by the sensor for sensitive human motion monitoring applications including large and small deformations. The results suggest the promising capability of the present sensor in reflecting the human body motion detection.

  • Influence of TiC content on mechanical, wear and corrosion properties of hot-pressed AZ91/TiC composites
    J. Compos. Mater. (IF 1.755) Pub Date : 2019-07-02
    Fatih Aydin; Yavuz Sun; M Emre Turan

    This study aims to investigate the mechanical, wear and corrosion performances of TiC reinforced AZ91 matrix composites. AZ91 alloy and AZ91/TiC composites with different weight fractions of 10, 20 and 30 (wt%) were fabricated by powder metallurgy incorporating hot pressing. Microstructure characterization shows that partial agglomeration of particles is present especially in AZ91/30 wt% TiC composite. The addition of TiC led to significant improvement in hardness and wear resistance. Observed wear mechanism is abrasive. As compared with AZ91, compressive yield strength and ultimate compressive strength of the composites were also significantly improved. On the other hand, corrosion rate increased with the addition of TiC particles by virtue of presence of the galvanic reactions.

  • A multidirectional damage model for fiber-reinforced plastic laminates under static load
    J. Compos. Mater. (IF 1.755) Pub Date : 2019-07-02
    Wenxuan Qi; Weixing Yao; Haojie Shen

    A multidirectional damage model based on continuum damage mechanics for fiber-reinforced composite laminates is proposed in this paper. The influence of three main damage mechanisms, including transverse matrix cracking, local delamination, and fiber breakage, on the multidirectional stiffness properties of composite laminates is analyzed by introducing macro phenomenological damage variables. Then the mechanical behavior of elementary ply in laminates is modeled based on these damage variables. Besides, relations between micro-level damage variables and macro-level damage variables are established. Damage evolution laws of the three damage mechanisms are proposed to predict the degradation of multidirectional stiffness and failure strength of composite laminates under quasi-static loading. The experiment of cross-ply glass fiber-reinforced plastic laminates is carried out, and the prediction results show good agreement with the experimental results.

  • Effects of environmental exposures on carbon fiber epoxy composites protected by metallic thin films
    J. Compos. Mater. (IF 1.755) Pub Date : 2019-07-01
    Arash Afshar; Dorina Mihut; Pengyu Chen

    Carbon fiber epoxy composites have a wide range of applications in aerospace, construction, and automotive industries due to their good mechanical properties and lightweight characteristics. Carbon fiber epoxy composite structures are typically intended for service in corrosive and hostile environmental conditions. Therefore, development of coatings which are able to protect carbon fiber epoxy composite laminates against prolonged and harsh environmental conditions such as ultraviolet radiation and moisture deems critical. This paper offers a novel method for environmental protection of fiber-reinforced polymer composites by applying thin metallic films on composites' surface as coating materials. In order to investigate the protective properties of metallic thin films, copper and aluminum coatings were deposited on the surface of carbon fiber epoxy specimens by using direct current magnetron-sputtering technique, and then mechanical properties and surface morphology of specimens were monitored during the course of accelerated environmental exposure. Both metallic coatings showed good adhesion to carbon fiber epoxy samples during environmental aging and provided protection for the specimens' surface against environmental degradation. The correlation between flexural properties and surface morphology of carbon fiber epoxy specimens is also presented.

  • Design of the ultrahigh molecular weight polyethylene composites with multiple nanoparticles: An artificial intelligence approach
    J. Compos. Mater. (IF 1.755) Pub Date : 2019-07-02
    A Vinoth; Shubhabrata Datta

    This study proposes a suitable composite material for acetabular cup replacements in hip joint that involves ultrahigh molecular weight polyethylene, a clinically proven material, as the matrix. To design new ultrahigh molecular weight polyethylene composites with multiple reinforcements for the improvement in mechanical and tribological performance, artificial neural network and genetic algorithm, the two artificial intelligence techniques, are employed. Published reports on the use of ultrahigh molecular weight polyethylene reinforced with multi-walled carbon nanotube and graphene are used as database to develop two artificial neural network models for Young's modulus and tensile strength. The optimum solutions are obtained using genetic algorithm, where the artificial neural network models are used as the objective functions. Two different composites, derived from the optimum solutions, are made reinforcing both multi-walled carbon nanotube and graphene. Tensile and wear tests show significant enhancement in the properties. The structures of the composites are also characterized, and wear mechanisms are discussed.

  • Impact damage assessment of carbon fiber reinforced composite with different stacking sequence
    J. Compos. Mater. (IF 1.755) Pub Date : 2019-07-03
    Rahul S Sikarwar; R Velmurugan

    This work examines the experimental and analytical investigation of impact on the carbon/epoxy laminates of various stacking sequence. The impact tests were carried out by using gas gun equipped with high-speed camera. Projectile velocities selected were 80 m/s and 30 m/s where 80 m/s was above ballistic limit velocity and 30 m/s was below ballistic limit velocity. The impact process was recorded with high-speed camera which facilitated to identify different energy absorbing mechanisms. High-speed images were also used to measure pre-impact and post-impact velocities of the projectile accompanied by photo diode and aluminum foil method. Total energy absorbed by the laminates, which is the difference between pre-impact and post-impact kinetic energy of the projectile, was calculated for the laminates with different stacking sequences. Damage extent in the laminates of different stacking sequences were also assessed by C-Scan of the laminates. Then effect of stacking sequences on damage extent and energy absorbing capacity was established. An analytical model was proposed to predict the residual velocity of the projectile at above ballistic limit velocity, which was based on the total energy absorbed by different energy absorption mechanisms. The analytical model was validated with experimental results for different stacking sequences. Additionally, effect of fiber orientation on damage shape at below ballistic limit velocity was also studied.

  • Thermally stimulated depolarization current characteristic of EVA–conductive PPy composites
    J. Compos. Mater. (IF 1.755) Pub Date : 2019-07-03
    F. S. Thabet; A. M. AbdElbary; G. M. Nasr

    Thermally stimulated depolarization current in pure poly(ethylene-co-vinyl acetate) and poly(ethylene-co-vinyl acetate) composites with different amounts of polypyrrole/carbon nanoparticles (of various weight ratios, 100:0, 95:5, 90:10, 85:15, 80:20, and 70:30) have been investigated at poling temperature 363 K using different polarizing voltage. Thermograms of pure and composite samples have two or three peaks over all temperature ranges depending on the polarizing voltage. The decrease in peak height with increased polarized voltage is observed in pure poly(ethylene-co-vinyl acetate) samples loaded with 5%, 10%, 15%, and 30% polypyrrole due to the detrapping of the large amounts of charge results in electrode blocking and decrease in thermally stimulated depolarization current in those samples. The molecular parameters, such as activation energy E, charge released Q, and relaxation times τ0 and τm for thermally stimulated depolarization current peaks have been estimated.

  • Evaluation of boron nitride nanoparticles on delamination in drilling carbon fiber epoxy nanocomposite materials
    J. Compos. Mater. (IF 1.755) Pub Date : 2019-07-03
    Halil Burak Kaybal; Ali Unuvar; Yusuf Kaynak; Ahmet Avcı

    The reinforcements of nanoparticles have an important role in improving the machinability of nanocomposite materials. Except for the known nanoparticles such as carbon nanotube, graphene, nanoclay, etc., the effect of boron nitride reinforcement on the machinability of composite materials are a recent research topic. In this study, boron nitride nanoparticle was introduced to the matrix resin that brings about additional strength and enhancement in thermal and mechanical properties of the composite. Though it was confirmed that this composition enhances the focused properties, it is necessary to investigate drilling performance of these composite and identify the effects of this boron nitride nanoparticle on machinability of carbon fiber epoxy nanocomposite considering thrust force, delamination factor, etc. Accordingly, while the thrust force is increased by reinforcement of the boron nitride nanoparticles, on the contrary of literature, delamination factor is tend to reduce as compared with reference composite. This experimental study shows the addition of boron nitride nanoparticles help to reduce delamination factor of carbon fiber epoxy nanocomposite. In addition, hole surfaces and drilling mechanism analyzed with optical and scanning electron microscope about damage estimation.

  • Quasi-static indentation damage and residual compressive failure analysis of carbon fiber composites using acoustic emission and micro-computed tomography
    J. Compos. Mater. (IF 1.755) Pub Date : 2019-07-04
    Yan-nan Zhang; Wei Zhou; Peng-fei Zhang

    In present research, the internal damage evolution and failure characteristics of carbon fiber woven composites under indentation and residual compressive loads were studied by using acoustic emission technology and X-ray micro-computed tomography. Real-time acoustic emission signals originating from internal damage of composites under applied loads were obtained and analyzed by the k-means clustering algorithm. Moreover, the internal damage characteristics were observed by the reconstructed three-dimensional model and the slice images of composite specimens. The results showed that the higher the indentation force reading, the more acoustic emission signals with high amplitude and frequency (over 300 kHz) are generated. Furthermore, the early acoustic emission signals with high-frequency were observed under residual compressive loads. It can be attributed to serious failures of fibers with the increase of static indentation loads. In addition, the internal damages such as delamination, debonding, crack and fiber breakage can be clearly characterized by micro-computed tomography and scanning electron microscopy observation. The complementary technology combing acoustic emission with micro-computed tomography can provide a better understanding of internal damages and evolution behaviors of the composites.

  • Macroscale bending large-deformation and microbuckling behavior of a unidirectional fiber-reinforced soft composite
    J. Compos. Mater. (IF 1.755) Pub Date : 2019-07-07
    Xin Lan; Sida Hao; Liwu Liu; Yanju Liu; Jinsong Leng

    Due to microscale fiber microbuckling, a fiber-reinforced soft composite demonstrates large macroscale bending deformation (e.g. 10% reversible macroscale compressive strain), which is larger than that of a convenient fiber-reinforced plastics (e.g. 1.5–2% elongation/compression at break). To investigate the deformation behavior, a normalized average energy density of a fiber-reinforced soft composite laminate was derived. By using a self-consistent approach according to the minimum energy principle, a series of analytical expressions were derived by a simplified theoretical method through solving simplified partial differential equations of average energy density. Furthermore, an improved numerical calculation method was developed using the full four terms of partial differential equations of average energy density by employing the results of simplified theoretical method as initial calculating values. The dimensionless results demonstrated that the trend correlated well between those two methods, and the improved numerical method obtained more accurate results than those of the simplified theoretical method. Analytical and numerical results in normalized expressions systematically descripted the bending large-deformation behavior including position of neutral surface and critical buckling, wavelength, amplitude, shearing strain, macroscale compressive/tensile strain, buckled fiber strain, and actuation moment. To design a fiber-reinforced soft composite for use in engineering, the simplified theoretical method is used to predict trend and obtain approximate results for preliminary design, and the improved numerical method is further used to check and obtain more accurate results on detailed design stage.

  • Water resistance, mechanical, and morphological characteristics in polyamide-6/zirconium phosphate nanocomposites
    J. Compos. Mater. (IF 1.755) Pub Date : 2019-07-10
    Daniela de França da Silva Freitas; Luis Claudio Mendes

    Polyamide-6/organointercalated zirconium phosphate nanocomposites (PA-6/ZrPOct) were prepared by melt extrusion. The synthesized lamellar ZrP was expanded with octadecylamine at different amine:phosphate ratio, and its influence was evaluated by tensile test, melt flow rate, water absorption, rheology, scanning electron microscopy, and wide-angle X-ray diffraction. For all nanocomposites, the increase of modulus and decrease of elongation at rupture were observed. The decrease in water uptake was observed as the amine/phosphate increase, indicating that the presence of the amine reduces the hydrophilic nature of PA-6. Rheology revealed by pseudoplasticity indices that the nanofillers dispersion was homogeneous in all nanocomposites. Wide-angle X-ray diffractometry analysis showed that the characteristic basal spacing peak of pristine ZrP was absent for ZrOct 1:1 and 2:1. Also a high decrease in crystallinity was observed for PA-6/ZrOct 2:1 sample, which would be associated to plasticizing effect of octadecylamine avoiding crystallites formation. Evidences showed that structures with different degrees of intercalation and/or exfoliation could have been achieved.

  • Performance of composite sandwich structures under thermal cycling
    J. Compos. Mater. (IF 1.755) Pub Date : 2019-07-10
    Sandesh Rathnavarma Hegde; Mehdi Hojjati

    Effect of thermally induced microcracks on mechanical performance of a space grade laminated sandwich panel is investigated. A simple non-contact setup using liquid nitrogen is developed to subject the material to low temperature of −170℃ with cooling rate of 24℃/min. Then the samples are exposed to the elevated temperature of 150℃ inside oven. Microcracks formation and propagation are monitored through microscopic observation of cross-section during the cycling. Flatwise tensile test is performed after a number of cycles. A correlation is made between number of cycles and flatwise mechanical strength after quantifying the microcracks. It is observed that the crack formation gets saturated at about 40 cycles, avoiding the need to conduct more thermal cycles. Microcrack formation both at the free edge and middle of laminate was observed. The crack density at the middle was comparatively less than the ones found on the free edges. Results for non-contact cooling are compared with samples from direct nitrogen contact cooling. Microscopic inspection and flatwise test show differences between contact and non-contact cooled samples. Flatwise tensile strength for non-contact cooled samples shows 15% reduction, while the contact cooled samples have about 30% decrease in bond strength. A 3D finite element analysis is conducted to qualitatively identify the location of stress concentration which can be possible sites of crack formation. Good agreement is observed between the model and experimental results.

  • Electrical, optical, and mechanical percolations of multi-walled carbon nanotube and carbon mesoporous-doped polystyrene composites
    J. Compos. Mater. (IF 1.755) Pub Date : 2019-06-27
    Ömer Bahadır Mergen; Ertan Arda; Gülşen Akın Evingür

    In this study, we have investigated and compared electrical, optical, and mechanical properties of polystyrene thin films with added multi-walled carbon nanotube and carbon mesoporous. Surface conductivity (σ), scattered light intensity (Isc), and all the mechanical parameters of these composites have increased with increasing the content of carbon filler (multi-walled carbon nanotube or carbon mesoporous) in the polystyrene composites. This behavior in electrical, mechanical, and optical properties of the polystyrene/carbon fiber composites has been explained by classical and site percolation theory, respectively. The electrical percolation thresholds (Rσ) were determined to be 8.0 wt% for polystyrene/multi-walled carbon nanotube and 25.0 wt% for polystyrene/carbon mesoporous composites. The optical percolation thresholds were found to be Rop = 0.8 wt.% for polystyrene/multi-walled carbon nanotube and Rop = 3.0 wt.% for polystyrene/carbon mesoporous composites. For the polystyrene/carbon mesoporous composite system, it was determined that the mechanical percolation threshold occurred at lower R values than the polystyrene/multi-walled carbon nanotube composite system. The electrical (βσ), optical (βop), and mechanical (βm) critical exponents have been calculated for both of the polystyrene/carbon fiber composites and obtained as compatible with used percolation theory.

  • Experimental and molecular dynamics study of boron nitride nanotube-reinforced polymethyl methacrylate composites
    J. Compos. Mater. (IF 1.755) Pub Date : 2019-05-15
    Sumit Sharma; Prince Setia; Rakesh Chandra; Nitin Thakur

    Heat dissipation is very essential for the efficient working of electronic devices. There is a widespread demand for high thermal conductivity materials. Boron nitride nanotubes have high thermal conductivity but due to their poor interfacial adhesion with polymers, their use as heat dissipating material is restricted. In this study, a silane-coupling agent has been used to modify the boron nitride nanotubes. These tubes were then inserted in polymethyl methacrylate matrix. Various properties such as thermal conductivity, storage modulus, and loss factor have been predicted. Molecular dynamics simulations have also been used for accurate prediction of the properties of boron nitride nanotubes/polymethyl methacrylate composites. The boron nitride nanotubes weight percentage was varied from 0% to 70% for studying the effect on thermal conductivity, storage modulus, and loss factor. The experimentally obtained thermal conductivity increased rapidly from 0.6 W/mK at 40 wt.% of boron nitride nanotubes to about 3.8 W/mK at 80 wt.% of boron nitride nanotubes in polymethyl methacrylate matrix (an increase of nearly 533%). A similar trend was obtained using molecular dynamics simulations. The storage modulus increased from 2 GPa (for pure polymethyl methacrylate) to about 5 GPa (for 70 wt.% boron nitride nanotubes). The glass transition temperature of boron nitride nanotubes/polymethyl methacrylate composites shifted to higher temperatures with an increase in boron nitride nanotubes weight percentage.

  • Experimental study on the bond behavior of the CFRP-steel interface under the freeze–thaw cycles
    J. Compos. Mater. (IF 1.755) Pub Date : 2019-06-26
    Yu-Yang Pang; Gang Wu; Hai-Tao Wang; Zhi-Long Su; Xiao-Yuan He

    The bond–slip degradation relationship between carbon fiber-reinforced polymer and steel in a freeze–thaw environment is crucial to evaluate the long-term service performance of steel structures strengthened with carbon fiber-reinforced polymer plates. However, limited studies on the durability and long-term performance of the carbon fiber-reinforced polymer-steel-bonded interface are the major obstacle for the application of carbon fiber-reinforced polymer plates in strengthening steel structures. This paper reports an experimental study to investigate the effects of the carbon fiber-reinforced polymer bond length and the freeze–thaw cycles on the bond behavior of the carbon fiber-reinforced polymer-steel-bonded interface. The three-dimensional digital image correlation technique is applied to obtain displacements and strains on the surface of the single-shear specimen. The experimental results present herein include the failure mode, the ultimate load, the carbon fiber-reinforced polymer strain distribution, the displacement distribution, and the bond–slip relationship. The results show that the ultimate load increases with increasing bond length until a certain bond length value is reached, after which the ultimate load remained approximately constant, and the ultimate loads of carbon fiber-reinforced polymer-steel interface decrease gradually under freeze–thaw cycles. The bond–slip parameters degradation models are proposed, and the bond–slip degradation relationship under the freeze–thaw cycles is established. Finally, the bond–slip degradation relationship is confirmed through comparisons with the experimental results.

  • Fabrication of bulk aluminum-graphene nanocomposite through friction stir alloying
    J. Compos. Mater. (IF 1.755) Pub Date : 2019-06-27
    Abhishek Sharma; Vyas Mani Sharma; Jinu Paul

    Friction stir alloying is primarily employed for the fabrication of surface composite to improve surface properties like hardness, wear resistance, and corrosion resistance without significantly affecting the bulk properties of the alloy. The present study demonstrates the novel method for the fabrication of bulk aluminum-graphene nanoplatelets composite by using friction stir alloying. Here, the novelty is shown through the method of graphene nanoplatelets incorporation in the stir zone. For this purpose, a channel is fabricated on the cross-sectional surface of the aluminum plate and filled with graphene nanoplatelets. It is then covered by the cross-sectional surface of another aluminum plate of same dimensions and friction stir alloying is carried out. Reference material (RM) is also fabricated at the same parameters without any graphene nanoplatelet reinforcements for the performance evaluation of the nanocomposite. The microhardness of the fabricated composite increased by ∼57% as compared to the reference material. However, the tensile strength of the fabricated Al-graphene nanoplatelet composites decreased marginally as compared to reference material. The strengthening of the composite is explained systematically by various mechanisms. The results of microhardness and tensile test were corroborated with various characterization methods such as optical micrographs, scanning electron microscopy, atomic force microscope, and X-ray diffraction.

  • Experimental investigation on the influence of carbon-based nanoparticle coating on the heat transfer characteristics of the microprocessor
    J. Compos. Mater. (IF 1.755) Pub Date : 2019-06-27
    Tamilarasi Thangamuthu; Rajasekar Rathanasamy; Saminathan Kulandaivelu; Ravichandran Kuttiappan; Mohanraj Thangamuthu; Moganapriya Chinnasamy; Velu Kaliyannan Gobinath

    In the current scenario, thermal management plays a vital role in electronic system design. The temperature of the electronic components should not exceed manufacturer-specified temperature levels in order to maintain safe operating range and service life. The reduction in heat build-up will certainly enhance the component life and reliability of the system. The aim of this research work is to analyze the effect of multi-walled carbon nanotube and graphene coating on the heat transfer capacity of a microprocessor used in personal computers. The performance of coating materials was investigated at three different usages of central processing unit. Multi-walled carbon nanotube-coated and graphene-coated microprocessors showed better enhancement in heat transfer as compared with uncoated microprocessors. Maximum decrease in heat build-up of 7 and 9℃ was achieved for multi-walled carbon nanotube-coated and graphene-coated microprocessors compared to pure substrate. From the results, graphene has been proven to be a suitable candidate for effective heat transfer compared to with multi-walled carbon nanotubes due to high thermal conductivity characteristics of the former compared to the latter.

  • Strain rate-dependent large deformation inelastic behavior of an epoxy resin
    J. Compos. Mater. (IF 1.755) Pub Date : 2019-06-27
    Sandeep Tamrakar; Raja Ganesh; Subramani Sockalingam; Bazle Z (Gama) Haque; John W Gillespie, Jr

    The objective of this paper is to model high strain rate and temperature-dependent response of an epoxy resin (DER 353 and bis(p-aminocyclohexyl) methane (PACM-20)) undergoing large inelastic strains under uniaxial compression. The model is decomposed into two regimes defined by the rate and temperature-dependent yield stress. Prior to yield, the model accounts for viscoelastic behavior. Post yield inelastic response incorporates the effects of strain rate and temperature including thermal softening caused by internal heat generation. The yield stress is dependent on both temperature and strain rate and is described by the Ree–Erying equation. Key experiments over the strain rate range of 0.001–12,000/s are conducted using an Instron testing machine and a split Hopkinson pressure bar. The effects of temperature (25–120 ℃) on yield stress are studied at low strain rates (0.001–0.1/s). Stress-relaxation tests are also carried out under various applied strain rates and temperatures to obtain characteristic relaxation time and equilibrium stress. The model is in excellent agreement over a wide range of strain rates and temperatures including temperature in the range of the glass transition. Case studies for a wide range of monotonic and varying strain rates and large strains are included to illustrate the capabilities of the model.

  • Characterization of carbon fiber-reinforced poly(phenylene sulfide) composites prepared with various compatibilizers
    J. Compos. Mater. (IF 1.755) Pub Date : 2019-06-27
    Bedriye U Durmaz; Ayse Aytac

    The aim of this study was to investigate the effects of different compatibilizers on the properties of polyamide-sized carbon fiber-reinforced poly(phenylene sulfide) composites. The composites were prepared by using melt blending and injection molding methods by using three different compatibilizers at various loading levels. The characterization of composites was performed by Fourier transform infrared spectroscopy, tensile test, dynamic mechanical analysis, differential scanning thermometer, thermogravimetric analysis and scanning electron microscope. According to tensile test results, the highest increment in tensile strength and strain at break values of composites was observed with the addition of Joncryl. According to scanning electron microscope and dynamic mechanical analysis results, the best interfacial adhesion between carbon fiber and poly(phenylene sulfide) was obtained by using Joncryl as the compatibilizer.

  • Eco-friendly castor oil-based UV-curable urethane acrylate zinc oxide nanocomposites: Synthesis and viscoelastic behavior
    J. Compos. Mater. (IF 1.755) Pub Date : 2019-06-29
    Abbas Madhi; Behzad S Hadavand

    Attention to environmental problems and the importance of maintaining it have caused the researchers to pay more attention in this regard. The production of polymers and resins has increased in recent years and has affected by environmental pollution due to their long-term degradation. An appropriate solution to this problem is the synthesis of degradable and environmentally friendly polymers and resins. Using natural materials in the synthesis of polymers and resins can help them to be environmentally friendly. The purpose of this research is to synthesize urethane acrylate resins using natural resources. For this purpose, the urethane acrylate pre-polymer was synthesized with castor oil. Then, using modified zinc oxide nanoparticles with 1, 3 and 5 wt% urethane acrylate zinc oxide nanocomposites were produced. The use of castor oil as a degradable part and lack of organic solvent in radiation systems led to the creation of an environmentally friendly resin. Subsequently, the viscoelastic behavior of the prepared nanocomposite was evaluated. Spectrometry results confirm the synthesized resin structure. The morphology of nanocomposites confirmed the proper particle size distribution in a 3 wt.% sample. The results of the dynamic mechanical thermal analysis test showed that increasing the amount of modified nano ZnO could increase the glass transition temperature, and the maximum value was observed in 5 wt.% modified nano ZnO (69.7℃).

  • Evaluation method for lightning damage of carbon fiber reinforced polymers subjected to multiple lightning strikes with different combinations of current components
    J. Compos. Mater. (IF 1.755) Pub Date : 2019-06-29
    Jinru Sun; Xueling Yao; Wenjun Xu; Jingliang Chen; Yi Wu

    The aircraft lightning environment consists of four lightning current components with different parameters, which are known as lightning components A, B, C and D. The lightning damage of aeronautic carbon fiber reinforced polymer laminates subjected to multiple continuous sequential lightning current components with different timing combinations was experimentally evaluated. The experimental results indicated that the carbon fiber reinforced polymer laminates suffered serious lightning damage, including carbon fiber fracture, resin pyrolysis and delamination. Through an analysis of the lightning damage properties of carbon fiber reinforced polymers, the influential factors and evaluation methods of the lightning damage in carbon fiber reinforced polymer laminates were studied. Because the lightning damage evaluation method under a single lightning impulse was found to be inapplicable for the multiple continuous lightning strikes, a multi-factor evaluation method was proposed. In the multiple continuous lightning strike test, the damage depth was found to be closely related to lightning components A, B and D and could be estimated based on the amplitudes and rise rates of the applied lightning components. Increases in the damaged area after a lightning strike were driven by lightning component C due to its substantial thermal effects. The damaged area was evaluated on the basis of the parameters of the electrical action integral and the transfer charge. The research on the evaluation methods for carbon fiber reinforced polymer laminate lightning damage presented herein may provide experimental support and a theoretical basis for studying the lightning effect mechanism and optimizing material formulations, manufacturing processes and structural designs to achieve performance improvements for carbon fiber reinforced polymer laminates in the future.

  • Numerical investigation of the effect of thermal gradients on curing performance of autoclaved laminates
    J. Compos. Mater. (IF 1.755) Pub Date : 2019-07-02
    Qing Wang; Lingyun Wang; Weidong Zhu; Qiang Xu; Yinglin Ke

    Autoclave curing process is one of the most frequently used manufacturing techniques of thermosetting composite materials. An efficient curing process requires good understanding of the thermal behavior of molds and composites during autoclave processing. In this paper, the effect of thermal gradients on curing performance of laminates is investigated through numerical approaches. In the first section, a computational fluid dynamics–finite element method numerical model is established to simulate the temperature field and the process-induced deformation of laminates. Then, a curved composite part with two different structures of mold is introduced to exhibit different temperature and degree of cure gradients during the autoclave process. Furthermore, by analyzing the position errors of measurement points, the deformation of the composite parts in different molds is evaluated. The results suggested that more synchronous curing process and less deformation of the composite part can be achieved by reducing the thermal gradients. In this specific case of a curved part, the range of position errors in X direction (the length direction) is reduced by 86.9% with the redesigned mold.

  • Guided Wave-based System for Real-time Cure Monitoring of Composites using Piezoelectric Discs and Phase-shifted Fiber Bragg Gratings.
    J. Compos. Mater. (IF 1.755) Pub Date : 2019-10-22
    Tyler B Hudson,Nicolas Auwaijan,Fuh-Gwo Yuan

    A real-time, in-process cure monitoring system employing a guided wave-based concept for carbon fiber reinforced polymer (CFRP) composites was developed. The system included a single piezoelectric disc that was bonded to the surface of the composite for excitation, and an embedded phase-shifted fiber Bragg grating (PS-FBG) for sensing. The PS-FBG almost simultaneously measured both quasi-static strain and the ultrasonic guided wave-based signals throughout the cure cycle. A traditional FBG was also used as a base for evaluating the high sensitivity of the PS-FBG sensor. Composite physical properties (degree of cure and glass transition temperature) were correlated to the amplitude and time of arrival of the guided wave-based measurements during the cure cycle. In addition, key state transitions (gelation and vitrification) were identified from the experimental data. The physical properties and state transitions were validated using cure process modeling software (e.g., RAVEN®). This system demonstrated the capability of using an embedded PS-FBG to sense a wide bandwidth of signals during cure. The distinct advantages of a fiber optic-based system include multiplexing of multiple gratings along a single optical fiber, small size compared to piezoelectric sensors, ability to embed or surface mount, utilization in harsh environments, electrically passive operation, and electromagnetic interference (EMI) immunity. The embedded PS-FBG fiber optic sensor can monitor the entire life-cycle of the composite structure from curing, post-cure/assembly, and in-service creating "smart structures".

  • Polymerization shrinkage and stress development in amorphous calcium phosphate/urethane dimethacrylate polymeric composites.
    J. Compos. Mater. (IF 1.755) Pub Date : 2010-02-20
    J M Antonucci,W F Regnault,D Skrtic

    This study explores how substituting a new high molecular mass oligomeric poly(ethylene glycol) extended urethane dimethacrylate (PEG-U) for 2-hydroxyethyl methacrylate (HEMA) in photo-activated urethane dimethacrylate (UDMA) resins affects degree of vinyl conversion (DC), polymerization shrinkage (PS), stress development (PSSD) and biaxial flexure strength (BFS) of their amorphous calcium phosphate (ACP) composites. The composites were prepared from four types of resins (UDMA, PEG-U, UDMA/HEMA and UDMA/PEG-U) and zirconia-hybridized ACP. Introducing PEG-U improved DC while not adversely affecting PS, PSSD and the BFS of composites. This improvement in DC is attributed to the long, more flexible structure between the vinyl groups of PEG-U and its higher molecular mass compared to poly(HEMA). The results imply that PEG-U has the potential to serve as an alternative to HEMA in dental and other biomedical applications.

    J. Compos. Mater. (IF 1.755) Pub Date : 2008-01-01
    J N R O'Donnell,J M Antonucci,D Skrtic

    Water sorption (WS), mechanical strength, and ion release of polymeric composites formulated with 40 % as-made or milled amorphous calcium phosphate (ACP) are compared after 1, 2 and 3 months of aqueous exposure. Ethoxylated bisphenol A dimethacrylate, triethylene glycol dimethacrylate, 2-hydroxyethyl methacrylate and methacryloxyethyl phthalate comprised the resin. The WS (mass %) peaked at 3 months. WS of as-made ACP composites was significantly higher than WS of milled ACP composites and copolymers. Both composite groups experienced decreases in biaxial flexural strength (BFS) with water aging, with milled ACP composites retaining a significantly higher BFS throughout immersion. Ion release was moderately reduced in milled ACP composites, though they remained superior to as-made ACP composites due to significantly lower WS and higher BFS after prolonged aqueous exposure.

  • Confined compression of dental composites for Class I restorations.
    J. Compos. Mater. (IF 1.755) Pub Date : 2011-08-23
    Amol S Patki,Murat Vural,Mike Gosz

    This study focuses on the mechanical response of a particle-reinforced restorative dental composite (Renew™) under proportional transverse confinement to understand the effects of stress multiaxiality on its mechanical and failure behaviors. We describe the confining ring technique as an experimental tool to introduce multiaxial compressive stress states in dental composites that realistically mimic three-dimensional stress states commonly experienced by dental restorations in the oral cavity. Effect of initial radial misfit between confining ring and specimen is analyzed through computational finite element simulations, and an analytical treatment of problem is also provided to compute the confining stress during elasto-plastic expansion of confining ring. Experimental results suggest that inelastic response of Renew composite is significantly influenced by hydrostatic stress component, and pressure-dependent yield functions are required to analyze plastic deformations and internal damage accumulation process.

  • Out-of-autoclave manufacturing of GLARE panels using resistance heating.
    J. Compos. Mater. (IF 1.755) Pub Date : 2018-11-18
    Bernhard Müller,Genevieve Palardy,Sofia Teixeira De Freitas,Jos Sinke

    Autoclave manufacturing of fibre metal laminates, such as GLARE, is an expensive process. Therefore, there is an increasing interest to find cost-effective out-of-autoclave manufacturing processes without diminishing the laminate quality. The aim of this study is to evaluate the quality of fibre metal laminate panels adhesively bonded and cured using resistance heating. Three manufacturing processes are compared for different layups with an embedded steel mesh at the mid-plane: autoclave curing, resistance bonding of two (autoclave-cured) panels and complete out-of-autoclave resistance curing of panels. Interlaminar shear strength tests and optical microscopy analysis showed that resistance bonding is a promising technique, leading to results comparable to autoclave curing. Resistance curing led to an interlaminar shear strength decrease of 30-60%. A study of the correlation between degree of cure and distance from the mesh revealed the potential of resistance bonding to be used for flexible embedded mesh geometries and on-site repairs.

  • Fatigue life and damage tolerance of postbuckled composite stiffened structures with indentation damage.
    J. Compos. Mater. (IF 1.755) Pub Date : 2018-10-30
    Carlos G Dávila,Chiara Bisagni

    The fatigue life and damage tolerance of composite stiffened panels with indentation damage are investigated experimentally using single-stringer compression specimens. The indentation damage was induced to one of the two flanges of the stringer of every panel. The advantages of indentation compared to impact are the simplicity of application, less dependence on boundary conditions, better controllability, and repeatability of the imparted damage. The tests were conducted using advanced instrumentation, including digital image correlation, passive thermography, and in situ ultrasonic scanning. Specimens with initial indentation damage ranging between 32 and 56 mm in length were tested quasi-statically and in fatigue, and the effects of cyclic load amplitude and damage size were studied. A means of comparison of the damage propagation rates and collapse loads based on a stress intensity measure and the Paris law is proposed. The stress intensity measure provides the means to compare the collapse loads of specimens with different damage types and damage sizes, while the Paris law is used to compare the damage propagation rates in specimens subjected to different cyclic loads. This approach enables a comparison of different tests and the potential identification of the effects that influence the fatigue lives and damage tolerance of postbuckled structures with defects.

  • Experimental investigation of reinforced bonded joints for composite laminates.
    J. Compos. Mater. (IF 1.755) Pub Date : 2018-03-24
    Chiara Bisagni,Domenico Furfari,Marco Pacchione

    An experimental study has been carried out to investigate the behaviour of co-bonded carbon fibre reinforced plastics joints with a novel design incorporating a through the thickness local reinforcement. Different specimens were manufactured to investigate static and fatigue behaviour, as well as delamination size after impact and damage tolerance characteristics. The mechanical performances of the specimens with local reinforcement, consisting of the insertion of spiked thin metal sheets between co-bonded laminates, were compared with those ones obtained from specimens with purely co-bonded joints. This novel design demonstrated by tests that damage progression under cycling load results significantly delayed by the reinforcements. A significant number of experimental results were obtained that can be used to define preliminary design guidelines.

  • Characterization and mechanical response of novel Al-(Mg–TiFe–SiC) metal matrix composites developed by stir casting technique
    J. Compos. Mater. (IF 1.755) Pub Date : 2019-05-21
    Samuel O Akinwamide; Serge M Lemika; Babatunde A Obadele; Ojo J Akinribide; Bolanle T Abe; Peter A Olubambi

    This study was conducted to investigate the synthesis, characterization and mechanical properties of aluminium reinforced with ferrotitanium and silicon carbide via stir casting technique. Microstructures of as-cast samples were analysed using optical and scanning electron microscopes equipped with energy-dispersive X-ray spectroscopy. The mechanical properties in terms of hardness, tensile, tribological behaviour and fracture were assessed. Results showed that the homogeneous dispersion of reinforcement was within the metal matrix composite. Tribological study revealed a decrease in frictional coefficient of the composites with lowest frictional coefficient observed in composite with addition of silicon carbide as reinforcement. Morphology of fractured surface displayed a reduction in the size of dimples formed in reinforced aluminium composites when compared with larger dimple sizes observed in as-cast aluminium alloy.

  • Testing, characterizing, and forming of glass twill fabric/polypropylene prepregs
    J. Compos. Mater. (IF 1.755) Pub Date : 2019-05-24
    Mingrui Liu; Lidong Wang; Xiongqi Peng

    This paper investigates the mechanical behaviors of thermoplastic woven prepregs via testing and forming experiments. Glass twill fabric/polypropylene prepregs are produced by chemical treatment on fabric surface and a hot pressure molding approach. Then, mechanical tests including uniaxial tensile and bias extension of the glass twill fabric and its prepregs are carried out to provide basic data set for material modelling. An anisotropic hyperelastic model based on strain energy decomposition is proposed. And its material parameters are obtained by fitting these experimental data. Hemispherical thermo-stamping experiments are implemented for model verification. Very good agreements between forming simulation results and experimental data including boundary profiles, local shear angles, and forming force magnitude are obtained. The present work provides a complete data set for the model development and verification of thermoplastic woven fabric prepregs.

  • Investigation of mechanical properties of nanostructured Al-SiC composite manufactured by accumulative roll bonding
    J. Compos. Mater. (IF 1.755) Pub Date : 2019-05-27
    AF Meselhy; MM Reda

    To manufacture high-strength, fine dispersed and uniform distribution of Al-5 vol.% SiC composite, accumulative roll bonding process is proposed and applied through this study. The microstructure illustrates and validates a good distribution of SiC reinforced in the Al 1050 matrix. It is found that after eight pass, the mean grain size of the composite sample is 188 nm. It can be concluded from tensile test that by increasing the number of passes the strengths of both Al ARBed and composite samples increase; however, their ductility decreases at the initial accumulative roll bonding pass and then increases. The tensile strength of Al-SiC composite sample is greater than the annealed Al 1050 used as the original raw material by five times. The strengthening of the proposed composite sample occurs due to grain refinement, uniformity, reinforcing role of particles, strain hardening, bonding quality and size of particles. From the hardness test, it is concluded that, after the initial pass, hardness increased quickly, then dwindled and finally saturated by further rolling. Observations discovered that the failure mode in the composite occurs due to the shear fracture. From the experimental investigation, governing equations are derived to describe the effect of the number of accumulative roll bonding passes on the tensile strength and elongation of manufactured metal matrix composite materials. It is found that the tensile strength and elongation can be described as an exponential function of the number of passes. Numerical results from these equations are more consistent with the experimental investigation.

  • Thermo-mechanical analysis of multilayered composite beams based on a new mixed global-local model
    J. Compos. Mater. (IF 1.755) Pub Date : 2019-05-27
    Qilin Jin; Ziming Mao; Xiaofei Hu; Weian Yao

    An accurate mixed-form global-local higher-order theory including transverse normal thermal deformation is developed for thermo-mechanical analysis of multilayered composite beams. Although transverse normal deformation is considered, the number of displacement parameters is not increased. The proposed mixed-form global-local higher-order theory is derived using the displacement assumptions of global-local higher-order theory in conjunction with the Reissner mixed variational theorem. Moreover, the mixed-form global-local higher-order theory retains a fixed number of displacement variables regardless of the number of layers. In order to obtain the improved transverse shear stresses, the three-dimensional equilibrium equation is used. It is significant that the second-order derivatives of in-plane displacement variables have been eliminated from the transverse shear stress field, such that the finite element implementation is greatly simplified. The benefit of the proposed mixed-form global-local higher-order theory is that no post-processing integration procedure is needed to accurately calculate the transverse shear stresses. The equilibrium equations and analytical solution of the proposed model can be obtained based on the Reissner mixed variational equation. The performance of the proposed model is assessed through different numerical examples, and the results show that the proposed model can better predict the thermo-mechanical responses of multilayered composite beams.

  • Mechanical, fire, and smoke behaviour of hybrid composites based on polyamide 6 with basalt/carbon fibres
    J. Compos. Mater. (IF 1.755) Pub Date : 2019-05-28
    Karolina Mazur; Stanislaw Kuciel; Kamila Salasinska

    This paper describes the hybridization of basalt and carbon fibres in polyamide 6 by injection moulding method and the analyses of the mechanical, morphological, fire, and smoke properties of the obtained materials. The content of basalt/carbon fibres in hybrid composites amounted to 5/5 wt%, 7/7 wt%, and 10/10 wt%. The addition of fibres resulted in an increase in mechanical properties of the examined materials, was reflected by the threefold increase of Young modulus for the composites containing 10/10 wt% of fibres. To investigate the aging, the samples were stored in distilled water for 1, 7, 14, 100, and 210 days. After 210 days, a significant decrease in mechanical properties was observed. Interestingly, the addition of fibres caused a 50% reduction in stiffness, whereas, in the case of neat polyamide 6, the decrease was about 78%. Additionally, the addition of fibres reduced water sorption. With the increasing fibre load, the decrease in the maximum average rate of heat emission was observed. In the case of composites containing 10 wt% of basalt fibres and 10 wt% of carbon fibres, it amounted to 207 kW/m2 and was lower by approx. 37% in comparison to the unmodified polymer.

  • Elaboration and mechanical properties analysis of a composite based on polyester resin reinforced with natural Alfa fibres
    J. Compos. Mater. (IF 1.755) Pub Date : 2019-05-28
    A Boukhoulda; FB Boukhoulda; H Makich; M Nouari; B Haddag

    In this paper, the elaboration process of a new composite material based on polyester resin reinforced with long Alfa fibres is described. The used Alfa fibres have been obtained using the chemical method of extraction based on alkali treatment with different percentage of sodium hydroxide (NaOH). The obtained average diameters of fibres treated with 9%, 10%, 11% and 14% NaOH concentrations are about 145 ± 35 µm, 90 ± 15 µm, 83 ± 15 µm and 75 ± 15 µm, respectively. The composite was elaborated with impregnation of the fabric Alfa fibres in polyester resin. Besides, an experimental characterization using tensile tests has been conducted to determine the mechanical properties of the fibres obtained with the different NaOH concentrations. The results show that the composite made of polyester resin reinforced with fibres treated with 9% concentration of NaOH presents the greatest tensile strength.

  • Micro-computed tomography analysis of natural fiber and bio-matrix tubular-braided composites
    J. Compos. Mater. (IF 1.755) Pub Date : 2019-05-29
    Brianna M Bruni-Bossio; Garrett W Melenka; Cagri Ayranci; Jason P Carey

    There is an increasing demand for the use of “green”-based materials as reinforcement and matrix materials in composites. However, the ability of these natural-based materials to perform as consistently and reliably as conventional materials is still relatively unknown. A key importance in the viability of these materials is the evaluation of the content of voids and imperfections, which may affect the properties of the entire composite. In this study, the microstructure of tubular-braided composites manufactured from cellulose fibers and a partially bio-derived resin was studied with the use of micro-computed tomography. These methods were used to determine the effect of modifying braid angle, resin type, and curing method on fiber volume fraction, void volume, and void distribution. It was determined that the void content increased with the increase in braid angle, and vacuum-bagging reduced the total void content. The sample with the smallest braid angle produced with vacuum-bagged curing contained a void fraction of 1.5%. The results of this study proved that the materials used could be viable for further testing and development and that micro-computed tomography imaging is valuable for identifying how to improve consistency and minimize imperfections to create more accurate and reliable natural fiber-braided composites.

  • Studying delamination in composite laminates using shell elements and a strain-rate-dependent micro-mechanical model
    J. Compos. Mater. (IF 1.755) Pub Date : 2019-05-29
    Sandeep Medikonda; Ala Tabiei

    The effectiveness of studying inter-laminar delamination in laminated composites with the help of thickness-stretch shell elements which utilize a 3-D material model sub-routine as compared to the traditional plane-stress shell elements has been investigated using a non-linear finite element solver (LS-DYNA®). A strain-rate-dependent micro-mechanical material model using ply-level progressive failure criteria has been used to simulate the initiation and propagation of delamination. A methodology of assigning physical significance to the choice of damage parameters has been presented. The numerical delamination growth has been qualitatively analyzed against the experimental C-scan images for multiple impact events on different composite plates.

  • Dielectric analysis as a low-complexity methodology for tracking prepreg out-time and its effects on the curing cycle
    J. Compos. Mater. (IF 1.755) Pub Date : 2019-05-29
    Olivia de Andrade Raponi; Bárbara Righetti de Souza; José Everardo Baldo Junior; Antonio Carlos Ancelotti Junior; Alessandro Guimarães

    The final properties of advanced composite parts manufactured from prepregs are strongly dependent on the combination of raw materials' properties and manufacturing parameters. Therefore, monitoring techniques that can characterize the prepreg cure advancement and the effects of this advancement on the curing process are of great interest to composite industries. In the present work, dielectric analyses were performed using a previously developed simple and low-cost device, as a successful alternative to track prepreg out-time and the specificities of aged prepregs curing process. The findings point out that, despite the temperature and humidity influence in the measurements, models for estimating prepreg out-times can be developed based on dielectric analyses results. Also, the dielectric properties can signalize the necessity of cure parameters adjustments, which might lead to the extension of prepreg out-time limits without significant detriment to the performance of the final part.

  • Fabrication and characterization of aluminum hybrid composites reinforced with silicon nitride/graphene nanoplatelet binary particles
    J. Compos. Mater. (IF 1.755) Pub Date : 2019-05-29
    Mahmut Can Şenel; Mevlüt Gürbüz; Erdem Koç

    In this study, pure aluminum was reinforced with pure silicon nitride (varying from 1 to 12 wt%), pure graphene nanoplatelets (changing from 0.1 to 0.5 wt%), and their hybrid form (silicon nitride/graphene nanoplatelets) by using powder metallurgy method. The results show that Vickers hardness increased to 57.5 ± 3 HV (Al-9Si3N4) and 57 ± 2.5 HV (Al-0.1GNPs) from 28 ± 2 HV (pure aluminum). Similarly, ultimate compressive strength of the pure silicon nitride and pure graphene nanoplatelet-reinforced aluminum composite was improved to 268 ± 6 MPa (Al-9Si3N4) and 138 ± 4 MPa (Al-0.5GNPs) from 106 ± 4 MPa (pure aluminum), respectively. Interestingly, the highest Vickers hardness, ultimate compressive strength, and ultimate tensile strength of aluminum-silicon nitride-graphene nanoplatelet hybrid composites were determined as 82 ± 3 HV (Al-9Si3N4-0.5GNPs), 334 ± 9 MPa (Al-9Si3N4-0.1GNPs), and 132 MPa (Al-9Si3N4-0.1GNPs), respectively. The Vickers hardness (for Al-9Si3N4-0.5GNPs), ultimate compressive strength (for Al-9Si3N4-0.1GNPs), and ultimate tensile strength (for Al-9Si3N4-0.1GNPs) improved ∼193%, ∼215%, and ∼47% when compared to pure Al, respectively. Above 9 wt% silicon nitride and 0.1 wt% graphene nanoplatelets content, an adverse effect was observed due to the agglomeration of silicon nitride and graphene nanoplatelets in aluminum matrix composites. Also, energy-dispersive X-ray and scanning electron microphotographs confirmed the presence of both silicon nitride and graphene nanoplatelets and uniformly distributed in the aluminum matrix.

  • Fabrication of aluminum-carbon nanotube nano-composite using aluminum-coated carbon nanotube precursor
    J. Compos. Mater. (IF 1.755) Pub Date : 2019-05-29
    Muhammad Mansoor; Shaheed Khan; Amjad Ali; Khalid Mahmood Ghauri

    Demand of special combination of different properties of the materials instigated the development of metal matrix composite. The carbon nanotubes being renowned for their excellent physical and mechanical properties are one of the major choices as strengthen material for metal matrix composites. To benefit their properties, the carbon nanotubes should be thoroughly dispersed and have wetting with the matrix. In the present study, a precursor of aluminum-carbon nanotubes was prepared by coating the nanotubes with titanium and used to fabricate the composite by induction melting. The precursor provided easy wetting, while induction melting facilitated dispersion of the nanotubes readily. Consequently, the composite exhibited noticeable augmentations in yield and tensile strength from 64 to 193 MPa and 81 to 227 MPa, respectively.

  • Finding the best sequence in flexible and stiff composite laminates interleaved by nanofibers
    J. Compos. Mater. (IF 1.755) Pub Date : 2019-06-02
    Hamed Saghafi; Seyed R Ghaffarian; Hesam Yademellat; Hossein Heidary

    The brittle nature of thermoset-based composite laminates restricts the application of these materials in various industries. One of the most effective methods for resolving this problem is interleaving the laminate by nanofibrous mats. Applying nanofibers between all layers is very costly and time-consuming. Therefore, the efficiency of using nanofibers in half of the layers for various interleaf sequences is investigated in this study. On the other hand, since the damage pattern is different in thick and thin laminates under impact, its effect is also considered. Cohesive parameters are required for impact modeling in ABAQUS, so they were obtained by mode-I and mode-II fracture tests and numerical studies. The results showed that the best position for interleaving the nanofibers is mid-layers and top layers (near impact point) in thin (flexible) and thick (stiff) laminates, respectively. If it is not possible to predict the damage penetration through the thickness, putting nanofibers in the top section of the laminate is suggested.

  • Three-dimensional nanoprepreg and nanostitched aramid/phenolic multiwall carbon nanotubes composites: Experimental determination of in-plane shear
    J. Compos. Mater. (IF 1.755) Pub Date : 2019-06-02
    Kadir Bilisik; Gulhan Erdogan; Erdal Sapanci; Sila Gungor

    In-plane shear of nanostitched three-dimensional para-aramid/phenolic composites were experimentally investigated. Adding the nanostitched fiber into nanoprepreg para-aramid fabric preform composites slightly improved their shear strengths. The carbon-stitched composite exhibited comparatively better performance compared to the para-aramid stitched composite probably due to well bonding between carbon fiber and phenolic resin. The stitched nano composites had mainly matrix breakages and micro shear hackles in the matrix; matrix debonding and filament pull-out in the composite interface; fibrillar peeling and stripping on the filaments due to angular deformation. This mechanism probably prohibited extensive interlaminar opening in the nanostitched composites. The result exhibited that the introducing of the nano stitched fiber where multiwall carbon nanotubes were transferred to the out-of-plane of the base structure enhanced its transverse fracture as a form of confined delamination area. Therefore, the damaged tolerance properties of the stitched nano composites were enhanced compared to the base.

  • Fabrication of graphene-magnetite multi-granule nanocluster composites for microwave absorption application
    J. Compos. Mater. (IF 1.755) Pub Date : 2019-06-04
    Boo H An; Bum C Park; Hamad A Yassi; Ji S Lee; Jung-Rae Park; Young K Kim; Jong E Ryu; Daniel S Choi

    Ferrite multi-granule nanoclusters are fabricated for microwave absorption materials in different sized particles and granules by modified polyol process. Various sizes of ferrite nanoclusters are placed on graphene-based composites and the behavior of their microwave absorbing properties is studied. The absorbing properties are measured using the free-space method with two horn antennas for X-band range (8.2 GHz–12.4 GHz). Relative permittivity and permeability values are calculated in measured frequency domain. The absorption coefficient changes by forming ferrite-graphene composites are presented as well.

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上海纽约大学William Glover