A new approach to enhancing interlaminar strength and galvanic corrosion resistance of CFRP/Mg laminates Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-11-15 Yingcai Pan, Xuan Wu, Zheng Huang, Guoqing Wu, Siqiang Sun, Hengjian Ye, Zongke Zhang
In the present research, AZ31 magnesium alloy was treated by electrochemical methods in Na2SiO3-KOH-KF and KOH-KF electrolytes, and the morphological features of films formed on magnesium alloy were assessed. Besides, the effect of Mg surface features on interlaminar failure load, failure mode and galvanic corrosion resistance of CFRP/Mg laminates were investigated. The results show that removal of silicate in the Na2SiO3-KOH-KF electrolyte can cause the transition of conversion film from ceramic-like oxide film to pitted oxide film. The pitted oxide film can effectively enhance the peel strength of CFRP/Mg laminates compared with the ceramic-like oxide film, and an average enhancement of 6.5 times was observed. The pitted oxide film on magnesium can provide an excellent protection against the galvanic corrosion in CFRP/Mg laminates as the ceramic-like oxide film.
Processability and tensile performance of continuous glass fiber/polyamide laminates for structural load-bearing applications Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-11-15 M. Nikforooz, M. Golzar, M.M. Shokrieh, J. Montesano
The performance of continuous E-glass/polyamide 6 laminates processed using distinct hot press moulding cycles was assessed and compared with similar E-glass/epoxy and E-glass/polypropylene laminates. The effects of peak processing temperature, preheating time, and temperature dwell time on laminate consolidation and quality were observed using optical and scanning electron microscopy. Corresponding quasi-static tensile tests were performed on 8, 8, [02/902]s and [±45]2s laminates. Compared to E-glass/epoxy composites, the 8 specimens presented a similar strength, while the 8 specimens exhibited a much lower strength due to weaker fiber/matrix adhesion. Conversely, the E-glass/polyamide cross-ply laminates had a markedly higher strength while exhibiting the same modulus. This is because of higher toughness; the polyamide matrix provides as was proved by higher transverse matrix cracking strain of E-glass/polyamide. These findings support the feasibility of producing cost-effective and high-quality E-glass/polyamide laminates for use in high-performance applications, which is an attractive alternative to more conventional glass/epoxy laminates.
Segregated conductive polymer composite with synergistically electrical and mechanical properties Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-11-13 Wei Zhai, Shuaiguo Zhao, Yan Wang, Guoqiang Zheng, Kun Dai, Chuntai Liu, Changyu Shen
The potential of segregated conductive polymer composites is greatly hampered due to its poor mechanical strength and brittle nature. In this work, plunger type injection molding (PTIM) is developed to achieve synergistically electrical and mechanical properties on carbon nanotubes (CNTs)/polypropylene (PP)/ultra-high molecular weight polyethylene (UHMWPE) segregated conductive polymer composite. Morphology observation indicates that the segregated CNTs conductive network was formed along the interfaces between PP and UHMWPE grains. An ultralow percolation threshold of 0.13 vol.% is achieved, which is much lower than that of conventional injection molding. The strength of PTIM sample is improved; importantly, more than 10 times of improvement in elongation at break has been achieved compared to the sample obtained from frequently-used compression molding. Stability of the segregated conductive network was evaluated through dynamic strain-sensing behaviors. This paper presents a meaningful strategy towards the improvement of comprehensive performance of segregated conductive polymer composite.
Hierarchical pseudo-ductile hybrid composites combining continuous and highly aligned discontinuous fibres Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-11-10 HaNa Yu, Marco L. Longana, Meisam Jalalvand, Michael R. Wisnom, Kevin D. Potter
Hybrid composites allow avoiding catastrophic failure, a key limitation of composite materials, and can provide a balanced suite of modulus, strength and ductility. The aim of this research is to manufacture hierarchical hybrid composites using a combination of continuous high elongation fibres and intermingled hybrids made out of highly aligned discontinuous fibres with lower elongation to achieve pseudo-ductility through control of failure development. The HiPerDiF (High Performance Discontinuous Fibres) method that allows a high level of fibre alignment, leading to excellent mechanical properties close to continuous fibre composites, was used to produce the intermingled hybrid discontinuous fibre preforms. The hierarchical hybrid composite configuration is composed of an intermingled hybrid discontinuous fibre layer sandwiched between continuous S-glass layers. The overall stress-strain response of the intermingled hybrid composites and the hierarchical hybrid composites was investigated for different fibre types and ratios. The analytical modelling approach previously developed by the authors for interlaminated hybrid composites was modified for this new type of hierarchical composite. The experimental results were analysed and the analytical model was used to evaluate the optimised balance of constituents to maximise pseudo-ductile strain in tension.
Carbon foam based on epoxy/novolac precursor as porous micro-filler of epoxy composites Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-11-10 Urszula Szeluga, Sławomira Pusz, Bogumiła Kumanek, Jerzy Myalski, Bartosz Hekner, Boyko Tsyntsarski, Rafał Oliwa, Barbara Trzebicka
The concept of application of crumbled carbon foam obtained from polymer precursor as a filler in polymer/carbon composite was described. The carbon foam used as powdered reinforcement of composites was prepared from epoxy resin cross-linked with phenol-formaldehyde resin (novolac) in a self-foaming process followed by carbonization at not very high temperature and ambient pressure. The structure of the carbon foam filler and resultant composites was studied by microscopic and spectroscopic methods. In the final composites, there were observed good quality dispersion of micronized grains of carbon foam, with the sizes that preserve their specific porous structure, in epoxy matrix and excellent adhesion at interfacial areas. The influence of the CF filler on the properties of resultant composites were investigated. Due to valuable properties of carbon foam, resultant composites occurred to have interesting characteristics: densities similar to those of pure polymer matrix, advantageous thermal and viscoelastic properties and enhanced tribological features.
A Model for the Time-dependent Compaction Response of Woven Fiber Textiles Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-11-07 Mario Danzi, Christoph Schneeberger, Paolo Ermanni
The description of the fiber bed compaction behavior is essential for the simulation of many composite manufacturing processes. In this study, we propose a material model describing the time-dependent compaction behavior of a dry fiber bed, valid for different fiber volume fractions and strain-rates. The approach is based on a linear generalized Maxwell model, in which stiffness parameters depend on strains, and relaxation times depend on strain-rates. The model parameters and functions are derived following an empirical approach, performing a curve fitting on multiple steps compaction experiments. The material considered is a carbon fiber woven fabric. The model response shows good agreement with the experimental results, proving the validity of the approach. The proposed material model uses only one set of equations to represent both the compaction and relaxation phases and can be easily implemented in numerical simulation tools.
Single Fiber Pull-Out Test of Regenerated Cellulose Fibers in Polypropylene: An Energetic Evaluation Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-11-07 J.-C. Zarges, C. Kaufhold, M. Feldmann, H.-P. Heim
This paper focuses on the energetic evaluation of the single fiber pull-out test (SFPT) using regenerated cellulose fibers (RCF) in a PP matrix with a varying MAPP content. Glass fibers were used for reference purposes. By means of the SFPT the interfacial shear strength (IFFS), the critical fiber length (lc), the consumed energy of a fiber pull-out and the consumed energy of a fiber rupture were determined. Results were related to the fiber length distribution in injection molded specimens. It was shown that theoretically more fiber ruptures appear in composites with RCF than with GF. But RCF composites offer a larger number of long fibers, slightly underneath the critical fiber length, consuming a high amount of energy by being pulled out at a composite failure. The consumed energy of a fiber pull-out per length was increased by using MAPP but simultaneously the critical fiber length was significantly reduced.
Influence of temperature on the strength of resistance welded glass fibre reinforced PPS joints Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-11-06 N. Koutras, I. Fernandez Villegas, R. Benedictus
In this work, the effect of temperature exposure on the strength of resistance welded joints is analysed. Glass fibre reinforced polyphenylene sulphide (GF/PPS) adherends were joined using the resistance welding technique, using a stainless steel mesh as the heating element. Single lap shear tests were performed at temperatures ranging between -50°C and 150°C to evaluate the strength of the welded joints. The results showed that the lap shear strength decreased with increasing temperature, except for the region between 50°C and 90°C where it remained constant. Fractography analysis revealed that the main failure mechanism was glass fibre/matrix debonding and the connection between the mesh and the matrix was not the weakest link at the interface of the joint at any temperatures under study. The fibre/matrix interfacial strength and the stress distribution at the joint overlap were identified as the main factors influencing the behaviour of lap shear strength with temperature.
Synergistic Effects of Spray-Coated Hybrid Carbon Nanoparticles for Enhanced Electrical and Thermal Surface Conductivity of CFRP Laminates Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-10-31 Yan Li, Han Zhang, Yi Liu, Huasheng Wang, Zhaohui Huang, Ton Peijs, Emiliano Bilotti
Carbon fibre reinforced plastics (CFRPs) are intensively used in modern aircraft structures because of their superb specific mechanical properties. Unfortunately their electrical and thermal conductivities are not sufficiently high for some applications like electromagnetic interference (EMI) shielding and lighting strike protection (LSP). The addition of external metallic structures, such as aluminium or copper mesh, is generally required, with a compromise in terms of increased mass and manufacturing cost as well as reduced corrosion resistance. In the present work spray coating of carbon nanoparticles was utilised as a simple method to locally increase the electrical and thermal suface conductivity of CFRPs. The combined use of carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs) synergistically reduced the CFRPs surface resistivity by four orders of magnitude (from 2-3 Ω/sq to 3×10-4 Ω/sq) and increased the thermal conductivity by more than 7 times (from 200 W⋅m-1⋅K-1 to 1500 W⋅m-1⋅K-1), opening up possibilities for the replacement of metallic mesh structures for EMI shielding and LSP. An analytical model was introduced based on a one-dimensional heat conduction approach to predict the effective thermal conductivity for the hybrid nanofiller coating layer and its findings showed good agreement with experimental data.
The use of shear-rate-dependent parameters to improve fiber orientation predictions for injection molded fiber composites Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-10-31 Huan-Chang Tseng, Rong-Yeu Chang, Chia-Hsiang Hsu
Fiber orientation distribution in injection molded fiber composites has an important shell-core structure. Recently, significant theoretical orientation models, including RSC (Reduced Strain Closure), ARD (Anisotropic Rotary Diffusion), and iARD-RPR (improved ARD and Retarding Principal Rate), have been widely applied in commercial injection molding simulation software. However, there is a long-running problem requiring an urgent solution for the state-of-the-art predictive models: obvious deviation of fiber orientation was found in the core region, although the orientation in the shell layer was predicted well. According to the fiber motions of flow-induced orientation, we therefore aimed to introduce a relationship between the model parameters and the shear rate. As validation, the shear-rate-dependent parameters can effectively enhance the prior orientation results for short-glass-fiber composites and long-carbon-fiber-composites in injection molding simulations, with good agreement between the present predictions and the experimental data obtained thereby.
Effect of yarn cross-sectional shape on resin flow through inter-yarn gaps in textile reinforcements Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-10-28 A. Endruweit, X. Zeng, M. Matveev, A.C. Long
Axial flow through gaps between aligned straight yarns with realistic cross-sectional shapes, described by power-ellipses, was analysed numerically. At a given fibre volume fraction, equivalent gap permeabilities have a maximum at minimum size of elongated tapering parts of the gap cross-section and a ratio of gap width to height near 1. When the yarn spacing is given in addition to the fibre volume fraction, calculated maximum and minimum values for the equivalent permeability of inter-yarn gaps, which occur at near-rectangular and lenticular cross-sections, differ by factors of up to 3.3. Novel approximations for the shape factor and the hydraulic diameter in Poiseuille flow were derived as a function of the fibre volume fraction, the yarn cross-sectional aspect ratio and the exponent describing the shape of the power-elliptical yarn cross-section. This allows the equivalent gap permeability to be predicted with good accuracy for any fibre volume fraction and yarn cross-section.
Largely enhanced dielectric properties of poly(vinylidene fluoride) composites achieved by adding polypyrrole-decorated graphene oxide Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-10-28 Zhen-zhen He, Xu Yu, Jing-hui Yang, Nan Zhang, Ting Huang, Yong Wang, Zuo-wan Zhou
Electrospinning of graphite/SiC hybrid nanowires with tunable dielectric and microwave absorption characteristics Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-10-28 Peng Wang, Laifei Cheng, Yani Zhang, Wenyu Yuan, Hongxing Pan, Heng Wu
This paper reports on the design and synthesis of tunable electromagnetic (EM) absorbers by encapsulating graphite into SiC nanowires. The hybrid nanowires with controllable dielectric and microwave absorption properties are employed for achieving tunable EM absorbers. The synthesis of the graphite/SiC hybrid nanowires was conducted by electrospinning and high temperature annealing. By simply controlling annealing temperature, the hybrid nanowires annealed at 1300 °C present a maximum reflection loss (RL) of −22 dB at 16.8 GHz with a small thickness of 1.7 mm and an effective absorption bandwidth (RL<-10dB, 90% EM wave absorption) covers from 8∼18 GHz. The excellent EM performance is attributed to the dielectric loss which originate from defects of graphite and SiC, interfaces between graphite and SiC, and dangling bond of nanowires surface. This work endows the nanowires potential to be utilized as reinforcements in polymers and ceramics for improving their EM performance with mechanical properties.
Hybrid welding of carbon-fiber reinforced epoxy based composites Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-10-23 Francesca Lionetto, Maria Nicolas Morillas, Silvio Pappadà, Giuseppe Buccoliero, Irene Fernandez Villegas, Alfonso Maffezzoli
The approach for joining thermosetting matrix composites (TSCs) proposed in this study is based on the use of a low melting co-cured thermoplastic film, added as a last ply in the stacking sequence of the composite laminate. During curing, the thermoplastic film partially penetrates in the first layer of the thermosetting composite, leading to macro-mechanical interlocking as the main connection mechanism between the thermoplastic film and the underlying composite. After curing, the thermosetting composite joints with the thermoplastic modified surface can be assembled by welding. Welding of the TSC-TSC joints is performed by ultrasonic and induction welding. The weld strength is investigated by morphological characterization of cross sections and failure surfaces and by mechanical testing. The effect of the thermoplastic film thickness on the welding process and on its outcome is also analyzed. Both induction and ultrasonic welding mostly result in good-quality welded joints. The welding process used as well as the initial thickness of the thermoplastic film are found to have a significant effect on the final thickness of the weld line and on the location of failure. Thicker thermoplastic films are found to ease the welding processes.
Enhanced dielectric properties through using mixed fillers consisting of nano-barium titanate/nickel hydroxide for polyvinylidene fluoride based composites Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-10-23 Yan Yang, Zhongyuan Li, Wenjing Ji, Chengxiao Sun, Hua Deng, Qiang Fu
The dispersion of nano-barium titanate(NBT) in polyvinylidene fluoride(PVDF) is one of the key issues in dielectric composites. Various NBT surface modification strategies which suffer from complex process and small-scale production have been reported. Herein, in-situ synthesized three-dimensional Ni(OH)2 is introduced to improve NBT dispersion in PVDF. During hydrothermal reaction, NBT aggregates are dispersed on the petals of in-situ grown Ni(OH)2 crystals as small aggregates. The three-dimensional structure of Ni(OH)2 can act as physical barrier to prohibit secondary agglomeration in PVDF to allow rather uniform NBT dispersion. Meanwhile, these hydroxyl groups on Ni(OH)2 ensures good interaction between filler and PVDF, and trigger β crystals. Comparing with NBT/PVDF containing the same amount of filler(2.5wt.%), the breakdown strength and maximum energy density containing mixed filler increases 14% and 70%, reach 282.6KV/mm and 6.13J.cm-3, respectively. This study provides a new approach to uniformly disperse nanofillers in polymer for enhanced dielectric properties.
Failure Mechanisms and Damage Evolution of Laminated Composites under Compression After Impact (CAI): Experimental and Numerical Study Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-10-23 X.C. Sun, S.R. Hallett
The damage tolerance of Carbon Fibre Reinforced Polymer (CFRP) to Barely Visible Impact Damage (BVID) is a critical design limiter for composite structures. This study investigated the key driving mechanisms and damage evolution of the compressive failure of laminated composites containing BVID using compression after impact and indentation (CAI) tests. Experiments were carried out on two similar quasi-isotropic laminates: [452/902/02/-452]2S and [45/90/0/-45]4S. Matrix cracking and delaminations were introduced by either low-velocity impact or quasi-static indentation tests prior to the CAI tests. The full-field displacement during CAI as well as the moment of rupture were captured by 3D Digital Image Correlation (DIC). The effect of ply-blocking and influence of factors, such as impact energy, delamination area and surface indentation, on compressive failure was studied. Previously validated high-fidelity finite element (FE) numerical models for the indentation and impact events were then used to investigate the damage evolution during CAI failure.
Electrical-based delamination crack monitoring in composites using z-pins Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-10-23 F. Pegorin, K. Pingkarawat, A.P. Mouritz
The in-situ, real-time detection of delamination cracks in composite materials using z-pins is reported. Carbon fibre-epoxy composites were reinforced in the through-thickness direction with different volume content (up to 4%) or material type (composite, metal) of z-pins. Z-pins can reduce the through-thickness electrical resistivity of composites by several orders of magnitude (up to ∼106), depending on their volume content and electrical properties. Z-pins create an electrically conductive pathway through-the-thickness of the otherwise resistive composite material (with an electrical resistivity of about 1.25 Ω.m). Mode I interlaminar tests performed under static fracture and cyclic fatigue load conditions reveal that z-pins can be used to detect delamination cracking via changes to the electrical resistivity. The sensitivity of z-pins to changes in the resistivity caused by crack growth is influenced by their volume content, electrical conductivity and interfacial bonding with the composite material.
Enhanced Thermomechanical and Electrical Properties of Multiwalled Carbon Nanotube Paper Reinforced Epoxy Laminar Composites Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-10-23 Sushant Sharma, Bhanu Pratap Singh, Sampat Singh Chauhan, Jeevan Jyoti, Abhishek Kr. Arya, S.R.Dhakate, Vipin Kumar, Tomohiro Yokozeki
Ply-orientation measurements in composites using structure-tensor analysis of volumetric ultrasonic data Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-10-23 L.J. Nelson, R.A. Smith, M. Mienczakowski
Ply wrinkling in carbon fibre reinforced polymer (CFRP) laminates is often geometrically complex and difficult to quantify using non-destructive techniques. In this paper, an ultrasonic technique for mapping ply wrinkling is presented. The instantaneous-phase three-dimensional dataset obtained from a pulse-echo ultrasonic inspection is processed using the structure-tensor image processing technique to quantify the orientations of the internal plies of a CFRP laminate. It is shown that consideration must be given to the wrapped nature of the phase dataset during processing to obtain accurate orientation maps. Three dimensional ply orientation and ply-location maps obtained from a test coupon are compared with true ply angles and locations by overlaying the ultrasonically-derived results on X-ray CT image slices, showing that accurate orientation maps can be obtained using the proposed technique.
Kinetics and temperature evolution during the bulk polymerization of methyl methacrylate for vacuum-assisted resin transfer molding Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-10-23 Yasuhito Suzuki, Dylan Cousins, Jerred Wassgren, Branden B. Kappes, John Dorgan, Aaron P. Stebner
Curing reactions of Methyl methacrylate (MMA) are comprised of an induction time of gradual temperature change over tens of minutes, followed by a sudden temperature rise within tens of seconds because of auto-acceleration known as the Trommsdorff effect. These curing effects were investigated as initial initiator and polymer concentrations were varied. A mathematical model combining the reaction kinetics with heat transfer was developed and verified in its ability to simulate the processing kinetics and temperature evolutions throughout thick MMA-based parts. It was further demonstrated that the processing conditions at specific points within a part during manufacture could be actively controlled via the Trommsdorff effect by locally varying the initial concentration of poly(methyl methacrylate) (PMMA) solution. Together, these advancements provide an enhanced ability to design and optimize the manufacture of thick, large scale PMMA fiber reinforced composites, taking advantage of auto-acceleration instead of avoiding it.
Aligned plasticized polylactic acid cellulose nanocomposite tapes: Effect of drawing conditions Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-10-19 Anshu Anjali Singh, Shiyu Geng, Natalia Herrera, Kristiina Oksman
Aligned nanocomposite tapes based on plasticized polylactic acid (PLA) and 1 wt.% cellulose nanofibers (CNF) were prepared using uniaxial solid-state drawing, and the effects of drawing conditions including temperature, speed and draw ratio on the material were studied. Microscopy studies confirmed alignment and the formation of ‘shish-kebab’ morphology in the drawn tape. Mechanical properties demonstrate that the solid-state drawing is a very effective way to produce stronger and tougher PLA nanocomposites, and the toughness can be improved 60 times compared to the undrawn tape. Additionally, the thermal properties, i.e. storage modulus, glass transition temperature and degree of crystallinity were improved. These improvements are expected due to the synergistic effect of CNF in the nanocomposite and orientations induced by the solid-state drawing.
Micro-CT measurement of fibre misalignment: application to carbon/epoxy laminates manufactured in autoclave and by vacuum assisted resin transfer moulding Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-10-19 Nghi Q. Nguyen, Mahoor Mehdikhani, Ilya Straumit, Larissa Gorbatikh, Larry Lessard, Stepan V. Lomov
This paper proposes a methodology for measurement of fibre misalignment in composite laminates based on the structure tensor of fibre orientations extracted from X-ray micro-computed tomography (micro-CT) images. The methodology is applied to carbon fibre/epoxy composites manufactured with two technologies: 1) by prepregging and consolidation in an autoclave and 2) by vacuum assisted resin transfer moulding. The results show that the in-plane inter-ply misalignment of fibres in the prepreg laminate and in the infusion-produced laminate is within 2-4° and 1-2°, respectively. The misalignment results allow better understanding of the manufacturing typical fibre orientation precision level for the low pressure (vacuum assisted resin transfer moulding) and high pressure (autoclave) manufacturing.
Exploring the potential of waste leaf sheath date palm fibres for composite reinforcement through a structural and mechanical analysis Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-10-16 Alain Bourmaud, Hom Dhakal, Anouck Habrant, Justine Padovani, David Siniscalco, Michael H. Ramage, Johnny Beaugrand, Darshil U. Shah
This work proposes a multi-scale study of the properties of leaf sheath date palm fibres currently considered as agricultural waste. Firstly, by using optical and electronic microscopy, two main types of bundles were identified which have profoundly different structures. Biochemical analysis and X-ray diffraction (XRD) revealed a low degree of crystallinity but a significant lignin content of about 17% giving the bundles a very cohesive structure as well as a good thermal stability in addition to a singular behaviour in dynamic vapour sorption. An average cell wall stiffness in the order of 16 GPa was highlighted by Atomic Force Microscopy in mechanical mode but tensile tests on bundles have revealed low stiffness and strength but a high elongation. These results combined with the cellular structure of these bundles, provides the potential of these wastes as cost effective and environmentally friendly composite reinforcements for high energy absorption and improved acoustics functions.
Drilling of Thick Composite Materials using a Step Gundrill Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-10-16 P. Rahme, Y. Landon, F. Lachaud, R. Piquet, P. Lagarrigue
The assembly of aeronautical parts requires the machining of composite materials. Drilling is the most important process in the assembly. When drilling composite materials, a number of defects are generating. A solution, to reduce these defects, is to drill using a step gundrill. In this paper, drilling of thick composite plates using a step gundrill is studied. Delamination, which is considered the major drilling defect, is analytically modelled at the hole exit. The critical thrust force at delamination is then found dividing the plate under the tool into several zones corresponding to the tool active part. These results are experimentally validated. The optimal cutting conditions at delamination are finally determined using a cutting force model. This model uses the same zones decomposition as the analytical critical thrust force model. The results of this paper can be extended to other tools to find the optimal cutting conditions corresponding for delamination-free drilling.
A New Approach to Characterising the Surface Integrity of Fibre-Reinforced Polymer Composites during Cutting Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-10-16 Weixing Xu, Liangchi Zhang
The surface integrity of a machined component influences its performance. For a fibre-reinforced polymer (FRP) composite, fragments in machining can be pushed into fractured surfaces, causing difficulties in the integrity examination experimentally. This paper presents a new numerical characterization method with the verification of microstructural examinations experimentally. Both conventional cutting and vibration- assisted cutting of unidirectional FRP composites with different fibre orientations were investigated. It was found that the new approach is convenient to show the fibre/matrix fracture and fibre-matrix debonding. The application of the method also revealed that fibre orientation significantly influences the final surface topography and subsurface damage, and that the vibration-assisted cutting can largely minimise the subsurface damage. When fibre bending or fibre crushing dominates the fracture of fibres in cutting, the method showed the surface roughness and subsurface damage of the machined FRP composite decreases with increasing the fibre orientation, and that the surface quality is the best when the fibres are aligned in the cutting direction.
Interaction of delaminations and matrix cracks in a CFRP plate, Part II: Simulation using an enriched shell finite element model Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-10-14 Mark W. McElroy, Renaud Gutkin, Mark Pankow
Numerical simulations are presented of a recently developed test which creates multiple delaminations in a CFRP laminate specimen that grow and interact via transverse matrix cracks . A novel shell element enriched with the Floating Node Method, and a damage algorithm based on the Virtual Crack Closure Technique, were used to successfully simulate the tests. Additionally, a 3D high mesh fidelity model based on cohesive zones and continuum damage mechanics was used to simulate the tests and act as a representative of other similar state-of-the-art high mesh fidelity modeling techniques to compare to the enriched shell element. The enriched shell and high mesh fidelity models had similar levels of accuracy and generally matched the experimental data. With runtimes of 36 minutes for the shell model and 55 hours for the high mesh fidelity model, the shell model is 92 times faster than the high-fidelity simulation.
Microcellular PP/GF composites: Morphological, mechanical and fracture characterization Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-10-13 J. Gómez-Monterde, M. Sánchez-Soto, M. Ll. Maspoch
The aim of the present work is to analyze the morphology, mechanical properties and fracture behaviour of solid and foamed plates made of glass fiber-reinforced PP. The morphology exhibited a solid skin/foamed core structure, dependent on the foaming ratio. Simulation of the microcellular injection molding process with Moldex 3D® software provided a good approach to the experimental results. The flexural properties and impact resistance showed lower values as the apparent density decreased, but constant specific properties. The fracture characterization was carried out by determining the Crack Tip Opening Displacement (CTOD) at low strain rate, as well as the fracture toughness (KIc) at impact loading. Foamed specimens presented higher values of CTOD than the solid ones and higher as the foaming ratio increases, due to cells acting as crack arrestors by blunting the crack tip. However, the fracture toughness KIc decreased with decreasing the apparent density. Anisotropy due to fiber orientation was also observed. Fibers were aligned in the filling direction in the surface layers, while they were oriented in the transverse direction in the core. According to the amount of fibers oriented in one direction or another, different properties were obtained.
Surface Modified Graphene Oxide Cross-linking with Hydroxyl-terminated Polybutadiene Polyurethane: Effects on Structure and Properties Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-10-13 Xiao Zhang, Jian Zheng, Haoming Fang, Yafei Zhang, Shulin Bai
Polyurethane (PU) based composites were fabricated by cross-linking hydroxyl-terminated polybutadiene (HTPB) chains with modified graphene oxide (MGO). The MGO worked as both the reinforcing agent and the cross-linker and strong interface between MGO sheets and PU matrix was formed, which provide the MGO/PU composites with well improved properties. Compared to neat PU and traditional direct-mixing GO/PU composites, the elastic modulus and tensile strength of 1 wt% MGO/PU composites increase significantly by 195.3% and 63.8%, respectively. Other properties such as thermal stability, anti-creep property and dynamic shear moduli are also much improved. All the improvements come from the enhanced interface bonding between MGO and PU, as well as dense molecular chains network in the composites. It can be expected that cross-linking method would be an effective fabrication approach and interface controlling strategy for the development of high-performance composites.
In-suit Mg(OH)2 template synthesis of nitrogen-doped porous carbon materials from glutinous rice for supercapacitors with excellent electrochemical performance Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-10-13 Hong-yang Tang, Rui Zhao, Huan Yin, Dong-xu He, Wei-dong Xue
In the present study, a new biomass-derived multilayer graphene-like low dimensional carbon material was prepared through the facile one-step carbonization of glutinous rice without conventional KOH chemical activation at 900°C in an argon atmosphere. The formation of disordered microporous and mesoporous on carbon, the high specific surface area of 1,371.50 m2 g-1, and the pore volume of 2.351 cm3 g-1 were confirmed by N2 adsorption and desorption. As a merit of its favorable structural features, the graphene-like carbon electrode exhibits an enhanced electric double layer capacitance (high specific capacitance of 289.9 F g-1 and 174 F g-1 at 0.5 A g-1 and 10 A g-1) and excellent cycling stability of 88% after 20,000 cycles at a current density of 8 A g-1. This observed electrochemical performance clearly indicates that activated carbon derived from glutinous rice could be used as a promising electrode material in a supercapacitor for electrochemical energy storage.
Do high frequency Acoustic emission events always represent fibre failure in CFRP laminates? Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-10-13 Fatih E. Oz, Nuri Ersoy, Stepan V. Lomov
When damage in carbon fibre reinforced composites (CFRP) is monitored by acoustic emission (AE), it is a common belief that high frequency AE events originate from fibre failure. Tihs shows that this statement may not correspond to the reality, and matrix cracks can emit high frequency AE signals. Quasi-static tension of [-452/02/+452/902]s laminates was monitored by AE, Digital Image Correlation (DIC) on the surface of the sample and in-situ optical microscopy on the sample’s polished edge. Unsupervised k-means clustering algorithm was applied to the AE results. By comparison with the direct DIC and microscopic observations, the AE cluster with high frequency and low amplitude was found to correspond to directly observed matrix cracks.
Squeeze flow in heterogeneous unidirectional discontinuous viscous prepreg laminates: experimental measurement and 3D modeling Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-10-13 G. Sorba, C. Binetruy, A. Leygue, S. Comas-Cardona
The freedom of composite design can be improved by combining continuous and discontinuous prepregs. The forming of a pre-heated blank made of optimally oriented and distributed discontinuous prepreg plies may lead to unacceptable defects such as in-plane and out-of-plane wrinkles, sliding of plies over long distance, rotation of adjacent plies, bending of fiber induced by transverse squeeze flow and finally to inappropriate and inefficient fiber distribution. This arises because the individual discontinuous plies are free to move and deform in the mold during the forming step. First, this paper presents some experiments conducted to identify the behaviour of a stack of unidirectional discontinuous viscous prepregs subjected to through-thickness compression. Then a model based on a heterogeneous anisotropic fluid approach is gradually developed in accordance with the experimental findings. It is shown that the various observed phenomena are retrieved by the numerical model and that the predicted values are in good agreement with measurements, but also that it requires to be solved in 3D with a relatively fine mesh in the thickness to provide good results.
Addition of nanoclay and compatibilized EPDM rubber for improved impact strength of epoxy glass fiber composites Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-10-12 Karanbir Singh, Tarun Nanda, Rajeev Mehta
Epoxy-glass fiber reinforced nanocomposites containing compatibilized ethylene propylene diene monomer (EPDM) rubber were processed for improved impact strength. Nanocomposites were reinforced with 1.0 weight percent of nanoclay and 2.5−10.0 weight percent of EPDM (both untreated and compatibilized). Compatibilization was done using two treatments: silane treatment and UV-assisted maleic anhydride grafting (MAH). SEM-EDS and FTIR confirmed EPDM treatment. SEM of fractured impact specimens was done to study effect of compatibilization on interfacial adhesion of nanocomposite constituents. XRD and TEM determined clay morphology in nanocomposites. EPDM concentration of 5.0 weight percentage resulted in maximum impact strength. For nanocomposites reinforced with silane treated EPDM, maximum improvement in impact strength was 68%, with a small drop in tensile properties. For MAH grafted EPDM, improvement in impact strength was 26%, but tensile properties recovered. Cavitation of rubber particles and improved interfacial adhesion of nanocomposite constituents were the main reasons for improved impact strength.
Micro-level Mechanisms of Fiber Waviness and Wrinkling during Hot Drape Forming of Unidirectional Prepreg Composites Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-10-10 K. Farnand, N. Zobeiry, A. Poursartip, G. Fernlund
Fiber misalignment in composites in the form of in-plane waviness and out of-plane wrinkling, is a major defect arising from processes such as hot drape forming. This work studies the micro-level mechanisms of forming in-plane fiber waviness and out-of-plane wrinkling. An out-of-autoclave unidirectional prepreg system by SOLVAY (CYTEC), CYCOM 5320/T650-35 was used to conduct multiple forming experiments and study the effects of various parameters including forming temperate and lay-up sequence. The effect of partial impregnation, or ‘Engineered Vacuum Channels’, in out-of-autoclave prepreg systems on the intra-ply separation/slippage and consequently fiber misalignment was studied and found to be a significant contributor to micro-level mechanisms. Cross sectioning and microscopy of the parts and examination of the end termination profiles were used to analyze the effect of forming parameters on ply end-shortening and consequently fiber misalignment.
Non-covalent functionalization of GO for improved mechanical performances of pectin composite films Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-10-07 Andreea Madalina Pandele, Corina Andronescu, Eugeniu Vasile, Ionut Cristian Radu, Paul Stanescu, Horia Iovu
The present work is aimed to develop new composite filmsbased on pectin and functionalized graphene oxide (GOf) by using a simple casting method. The non-covalent functionalization of graphene oxide (GO) was performed by using a non-ionic surfactant (Tergitol NP9) and therefore the interaction between GO and the polymer matrix was significantly enhanced. X-ray diffraction (XRD), X-ray photoelectron spectrometry (XPS) and Fourier-transform infrared (FT-IR) were used to prove the GO functionalization. The functionalization was evidenced also by Raman spectrometry and thermogravimetric analysis (TGA). According to the mechanical tests, an improvement of the Young’s modulus was recorded even at low loading of GOf within the pectin matrix which indicates a strong interaction between the polymer and GOf. By incorporation of GOfwithin pectin a modification of the morphology of the composite materials was observed by Atomic Force Microscopy (AFM) and Scanning Electron Microscopy(SEM) analysis.
Thermal conductivities of PU composites with graphene aerogels reduced by different methods Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-10-06 An Li, Cong Zhang, Yang-Fei Zhang
Thermal management has become a serious problem with development of miniaturized, high integration and high performance electronics devices, where the improvement of thermal conductivity on polymer composites is crucial for the internal heat transfer and dissipation. In this work, graphene aerogels (GA) with three-dimensional (3D) structure were prepared by a simple method and reduced by different ways. Then, GA were used as fillers to prepare high thermal conductivity polymer composites. A thermal conductivity of 3.36 W m-1K-1 at room temperature was obtained when use polyurethane filling the hydroiodic acid reduced GA composite (HI-RGA/PU), and the graphene loading was as low as 2.5 wt.%. This result is better than most researches of polymer-based thermal conductive composites. Furthermore, the heat transfer test and thermal cycling test show that HI-RGA/PU has a good and stable performance in the practical application as thermal interface material (TIM), which proves that GA is a promising filler for thermal conductive material.
Anti-hydrolysis effect of aromatic carbodiimide in poly(lactic acid)/wood flour composites Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-10-05 Pavlina Holcapkova, Petr Stloukal, Pavel Kucharczyk, Maria Omastova, Adriana Kovalcik
Poly(lactic acid) (PLA) filled with wood flour (WF) is more susceptible to hydrolysis compared to pure PLA. This work shows that the hydrolysis reactions leading to chain scission can be hindered by using 2 wt% of bis(2,6-diisopropylphenyl)carbodiimide (ZIKA). It was found that the addition of ZIKA supports the crosslinking of PLA/WF composite. The crosslinking slightly hindered the annealing efficiency of wood flour and increased the stiffness of biocomposites. The thermal stability of biocomposites containing ZIKA was slightly improved. The relevance of the antihydrolysis effect of ZIKA during melt processing of biocomposites was correlated with the rheological and molar mass properties. The hydrolytic stability of biocomposites was determined under buffer solution conditions at accelerated temperature 80 °C and pH of 7. The determined lower depolymerisation and hydrolysis rates of PLA/WF-ZIKA composites indicate that the service lifespan of biocomposites can be prolonged by the addition of ZIKA additive.
Property Improvements of CNT Films Induced by Wet-Stretching and Tension-Heating Post Treatments Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-10-04 Shaokai Wang, Qianli Liu, Min Li, Tianshu Li, Yizhuo Gu, Qingwen Li, Zuoguang Zhang
Various stretching and heating treatments were conducted on a carbon nanotube (CNT) film, so as to transfer the excellent properties of individual CNTs into a useful material. It shows that the wet-stretching improves the tensile strength and modulus to 2.3 and 5.9 times of the CNT film treated by traditionally dry stretching. Inspired by carbonization process of carbon fiber, tension force was further applied on the CNT film during subsequent heat treatment. Therefore, tensile strength and modulus of the CNT film are dramatically improved to 6.3 and 39.7 times respectively comparing with the as-prepared film. The tensile modulus reaches up to 127.1 GPa, far beyond most reported moduli of nanocarbon-based films and papers. Herein, the higher tensile moduli of the post-treated CNT films the smaller fracture elongation. Moreover, the post-treated CNT film manifests stable piezoresistive behavior with the gauge factor of 13.2, indicating of good sensitivity of the network.
Mechanical properties and reinforcing mechanisms of cementitious composites with different types of multiwalled carbon nanotubes Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-10-04 Xia Cui, Baoguo Han, Qiaofeng Zheng, Xun Yu, Sufen Dong, Liqing Zhang, Jinping Ou
In this study, reinforcement effect of 12 types of multiwalled carbon nanotubes (MWCNTs) on mechanical properties of cementitious composites was investigated Research results showed that among pristine MWCNTs with different diameters and lengths, the short MWCNTs with large diameter present the best reinforcing effect on strength of composites. Functionalization of MWCNTs is beneficial for enhancing strength of composites. Moreover, hydroxyl-functionalized MWCNTs feature a better reinforcement effect compared to carboxyl-functionalized MWCNTs. The best relative/absolute enhancements of 79%/74MPa and 64.4%/5.6MPa in compressive and flexural strength of composites are achieved by incorporating 0.5% of nickel-coated MWCNTs. XRD analyses revealed that the incorporation of MWCNTs decreases the orientation of CH in matrix, which is consistent with SEM observations. TG analyses showed that MWCNTs inhibit hydration of composites due to their absorption effect. However, extensive MWCNT networks improve microstructure of matrix and hinder the crack development under loading through fiber bridging and pull-out.
Thermal superinsulating silica aerogels reinforced with short man-made cellulose fibers Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-10-03 Julien Jaxel, Gediminas Markevicius, Arnaud Rigacci, Tatiana Budtova
Short man-made cellulose fibers (TENCEL® fibers) were used to mechanically reinforce thermal superinsulating silica aerogels. The aerogels were prepared via two drying techniques: ambient pressure drying and with supercritical CO2, in both cases resulting in monolithic non-brittle materials. The influence of fiber length and concentration on the thermal conductivity and flexural properties of both types of composite aerogels was evaluated. Thermal conductivity in room conditions varied from 0.015 to 0.018 W.K-1.m-1; it slightly increased with fiber concentration but remained in superinsulation domain. The importance of fiber percolation concentration for synthesizing monolithic ambient pressure dried composite aerogels was demonstrated. Contrary to neat silica aerogels, non-brittle behavior was observed for composite aerogels regardless of the drying method when reinforced with cellulose fibers. Macroscopic short cellulose based fibers are efficient and easy to use for preparing robust, monolithic, thermal superinsulating aerogel materials.
Process-Induced Strain and Distortion in Curved Composites. Part II: Parametric study and application Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-10-03 Kazunori Takagaki, Shu Minakuchi, Nobuo Takeda
Process-induced shape distortion is generated in curved composite parts. In the accompanying paper, the authors developed a fiber-optic monitoring method and confirmed that chemical cure shrinkage induces through-thickness shear deformation, which is the key deformation affecting final shape. The present paper first investigated the effects of thickness, flange length, and shape on internal states and process-induced deformation. Shear deformation was suppressed as the part thickness decreased and the flange length increased, resulting in larger spring-in. The shape effect was evaluated by comparing L- and U-shaped components. Larger warpage and spring-in were generated in the U-shaped part, indiacting that deformation in a U-shaped part is not a simple superposition of two L-shaped parts. Finally, a curved ply drop-off structure was investigated as a practical example. Internal strain was uniform in parts of different thickness, whereas residual deformation was non-uniform in the longitudinal direction due to mechanical coupling between the two parts.
Process-Induced Strain and Distortion in Curved Composites. Part I: Development of Fiber-Optic Strain Monitoring Technique and Analytical Methods. Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-10-03 Kazunori Takagaki, Shu Minakuchi, Nobuo Takeda
Process-induced shape distortion is generated in curved composite parts. Although the distortion mechanisms have been understood through considerable previous efforts, they were validated by indirect methods such as shape measurement, leaving some room for discussion. The present work developed a novel direct method using in-situ fiber-optic-based monitoring of through-thickness normal and shear strains. This method was applied to an L-shaped CFRP part and the result indicated that chemical cure shrinkage induces shear deformation. Moreover, the phenomenon gradually changed from shear-dominated to bending-dominated deformation as curing proceeded. The shear-lag analysis developed in previous work was then extended to L-shaped parts. The effects of flanges and edge constraints were investigated based on analytical and experiment results. The analysis also proposed a spring-in prediction scheme that uses strain monitoring results as inputs. The prediction agreed with the experiment result, indicating that cure-induced shear deformation should be considered for highly precise distortion prediction.
Viscoelastic distortion in asymmetric plates during post curing Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-09-30 María Benavente, Lionel Marcin, Alice Courtois, Martin Lévesque, Edu Ruiz
This study aims at understanding the geometrical instability triggered by the residual stresses generated during the manufacturing and post-curing of composites plates. Asymmetric plates with a [0/90] configuration were manufactured by Resin Transfer Molding (RTM). Manufactured plates were reheated free standing in an convection oven to study their behavior at high temperatures. Digital image analysis was used to monitor the plates curvature evolution with time and temperature. The experimental results of this work demonstrates the impact of the resin’s viscoelastic behavior on the geometrical distortion generated by residual stresses in asymmetric plates at high temperatures.
Electrical, morphological and thermal properties of microinjection molded polyamide 6/multi-walled carbon nanotubes nanocomposites Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-09-25 Shengtai Zhou, Andrew N. Hrymak, Musa R. Kamal
A series of polyamide 6/multi-walled carbon nanotubes (PA6/CNT) nanocomposites were prepared using a masterbatch dilution process, followed by microinjection molding of a part with a three-step decrease in thickness along the flow direction. Morphology observations revealed that there was a preferential orientation of CNT in the flow direction, which is attributed to the prevailing high shear rates in µIM. The distribution of CNT after melt processing was evaluated by dissolving experiments. Additionally, the correlation between electrical resistivity and development of microstructure for each section of the microparts was considered. The thermal behavior of PA6/CNT nanocomposites and corresponding microparts was evaluated using differential scanning calorimetry. Results indicated that the addition of CNT had little effect on the melting behavior of PA6/CNT nanocomposites and corresponding microparts. However, the crystallization behavior was changed significantly and a double crystallization peak was observed for samples incorporating CNT.
Interaction of delaminations and matrix cracks in a CFRP plate, Part I: A test method for model validation Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-09-22 Mark McElroy, Wade Jackson, Robin Olsson, Peter Hellström, Spyros Tsampas, Mark Pankow
Isolating and observing the damage mechanisms associated with low-velocity impact in composites using traditional experiments can be challenging, due to damage process complexity and high strain rates. In this work, a new test method is presented that provides a means to study, in detail, the interaction of common impact damage mechanisms, namely delamination, matrix cracking, and delamination-migration, in a context less challenging than a real impact event. Carbon fiber reinforced polymer specimens containing a thin insert in one region were loaded in a biaxial-bending state of deformation. As a result, three-dimensional damage processes, involving delaminations at no more than three different interfaces that interact with one another via transverse matrix cracks, were observed and documented using ultrasonic testing and x-ray computed tomography. The data generated by the test is intended for use in numerical model validation. Simulations of this test are included in Part II of this paper.
Effects of surface modification on dispersion, mechanical, thermal and dynamic mechanical properties of injection molded PLA-hydroxyapatite composites Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-09-21 John O. Akindoyo, Mohammad D.H. Beg, S. Ghazali, Hans P. Heim, Maik Feldmann
In this study, poly(lactic acid) (PLA)/hydroxyapatite (HA) composites were produced through extrusion and injection moulding. In order to foster good interaction between PLA and HA, a phosphate based modifier (Fabulase(R) 361) was used to modify the HA surface. Spectroscopic analysis reveals that surface of the HA was effectively modified without changing the HA into another material. Morphological study shows effective dispersion of HA in the PLA matrix after modification, with significant influence on the composite properties. Thermal properties of the modified HA composite was improved, alongside an enhancement of about 25%, 20% and 42% in tensile, modulus and impact properties of the modified PLA-HA composite respectively. Furthermore, dynamic properties of the modified HA composite was notably improved with obvious reduction of the damping factor. Thus, surface modification was effective to enhance dispersion and compatibility of HA and PLA to produce polymeric biomaterials suitable for good load bearing applications.
Improving thermal and flame retardant properties of epoxy resin by functionalized graphene containing phosphorous, nitrogen and silicon elements Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-09-20 Yuezhan Feng, Chengen He, Yingfeng Wen, Yunsheng Ye, Xingping Zhou, Xiaolin Xie, Yiu-Wing Mai
As alternative flame-retardant additive for polymers, reduced graphene oxide (RGO) is often limited by its poor interfacial compatibility with matrix. In this work, a new flame retardant, containing phosphorous, nitrogen and silicon elements was used to functionalize RGO. The wrapped flame retardant chains induced the improvement in the dispersion and compatibility of RGO in epoxy (EP) matrix. As a result, the mechanical, thermal and flame retardant properties of EP-based composites were significantly improved by adding flame retardant-functionalized RGO. The peak heat release rate, total heat release and total smoke production reduced by 34%, 14% and 30%, respectively, compared to neat resin. Based the char analyses, the enhancement in flame retardancy is attributed to the outstanding char layers with high strength and thermal stability resulting from the template effect of graphene, the charring effect of phosphorus and nitrogen elements and the enhancing effect of silicon element in grafted flame retardant chains.
The effect of fiber undulation on the strain field for pinned composite/titanium joints under tension Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-09-20 L Eberl, Avila Gray L, S Zaremba, K Drechsler
The way fiber undulation around pins affects pinned composite/titanium joints’ stiffness and strength properties is illustrated for double-lap-shear joints under quasi-static tensile loading. 3D digital-image-correlation techniques were employed to measure in-plane strain distribution on the surface of the composite joint member. Pinned joints with formed holes and three different composite stacking sequences were manufactured and compared to joints with drilled holes. Whereas in the case of joints with formed holes, the process of inserting the pin into uncured prepreg material created undulations, joints with drilled holes are characterized by a uniform fiber direction but partly broken fibers. Due to homogenization of the strain field within the load-carrying 0° layers, pinned composite/metal joints with formed holes proved to significantly outperform joints with drilled holes in terms of tensile stiffness and strength.
An effective route for the fabrication of multi-walled carbon nanotubes-reinforced ROMP-based nanocomposites by solution casting technique Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-09-17 Guang Yang, Jing Yan, Young Gyu Jeong, Jong Keun Lee
This work reported the solvent-soluble multi-walled carbon nanotubes (MWCNTs), which could be used for the fabrication of ring-opening metathesis polymerization (ROMP)-based nanocomposites by solution casting technique. As the first and most important step of the solution casting technique, the excellent dispersibility of the MWCNTs in different solvents was achieved by the functionalization of the nanotube surface with norbornene oligomers. The norbornene-functionalized MWCNTs (nMWCNTs) had outstanding dispersion stability in water, tetrahydrofuran (THF), acetone, and ethanol, especially the maximum nanotube concentration of 3.9 mg/mL in THF. The incorporation of nMWCNTs into poly(5-ethylidene-2-norbornene) (poly(ENB)) by solution casting technique resulted in significant improvements in the mechanical properties over the neat poly(ENB) and the pristine MWCNT-reinforced poly(ENB) nanocomposites. The route developed here not only avoids the dramatic increase of the viscosity occurring in the bulk polymerization but also provides the feasibility of high loadings of MWCNT reinforcements, consequently broadening the potential applications of ROMP-based nanocomposites.
Hybrid Bicomponent Fibres for Thermoplastic Composite Preforms Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-09-15 Christoph Schneeberger, Joanna C.H. Wong, Paolo Ermanni
Hybrid bicomponent fibres – materials in which reinforcement fibres are individually sheathed in thermoplastic polymer – are proposed as a novel class of preform materials for thermoplastic composites. We assert that by reducing the scale of hybridization between the reinforcement fibres and the matrix polymer to the level of the fibre, a thermoplastic intermediate material with both high drapeability and short consolidation times can be developed. The manufacture of hybrid bicomponent fibres is demonstrated in a scalable, coating process in which glass fibres are combined with several thermoplastic polymer matrix systems in dimensions and proportions suitable for use in thermoplastic composite structures. This novel class of thermoplastic composite preforms is expected to expedite the high volume production of geometrically complex thermoplastic composite parts.
In-situ space-confined synthesis of well-dispersed three-dimensional graphene/carbon nanotube hybrid reinforced copper nanocomposites with balanced strength and ductility Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-09-13 Xiang Zhang, Chunsheng Shi, Enzuo Liu, Fang He, Liying Ma, Qunying Li, Jiajun Li, Naiqin Zhao, Chunnian He
It is a tough issue to design and fabricate discontinuously reinforced metal matrix composites (DRMMCs) with desired mechanical and physical properties. Utilizing nanocarbon materials such as one-dimensional (1D) carbon nanotubes (CNTs), two-dimensional (2D) graphene or their hybrids as reinforcements for DRMMCs is now considered to be a good solution because of their outstanding intrinsic characterizations. In this work, we proposed a novel in-situ space-confined strategy to circumvent the problem of the controllable interconnection and bonding between CNTs and graphene and thus constructed a well-dispersed CNTs embedded in three-dimensional graphene network (3D GN) hybrid structure for fabricating reinforced Cu matrix nanocomposites. The as-obtained 3D GN/CNT hybrids reinforced copper bulk nanocomposites exhibited a significant strengthening efficiency and a more balanced strength vs. ductility relation compared with Cu matrix composites reinforced by single component (CNT or 3D GN) with the same volume fraction.
The importance of translaminar fracture toughness for the penetration impact behaviour of woven carbon/glass hybrid composites Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-09-11 Yentl Swolfs, Yoran Geboes, Larissa Gorbatikh, Silvestre T. Pinho
The impact resistance of fibre-reinforced composites is vital in many applications, and can be improved by exploiting synergies in fibre-hybridisation. These effects are however not sufficiently well understood in the literature. Penetration impact tests were hence performed on carbon/glass hybrids, and the results were linked to the flexural behaviour and translaminar fracture toughness. The results revealed large synergetic effects of up to 40% compared to the linear rule-of-mixtures. The results are also the first to reveal that creating a translaminar fracture surface can strongly contribute to the energy absorbed during penetration impact: 56% for an all-carbon fibre composite and 13% for an all-glass fibre composite. These results prove that strategies for maximising the translaminar fracture toughness can also be exploited to maximise the penetration impact resistance of fibre-hybrids. In carbon fibre composites in particular, ply blocking, using larger yarns and introducing micro-cuts should therefore increase the penetration impact resistance.
New BN-epoxy composites obtained by thermal latent cationic curing with enhanced thermal conductivity Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-09-09 Isaac Isarn, Lluís Massagués, Xavier Ramis, Àngels Serra, Francesc Ferrando
A series of boron nitride (BN) composites, with different BN content, were prepared and characterized by cationic curing of DGEBA/BN formulations. As cationic initiator a commercial benzylanilinium salt was used. This cationic system shows good latent characteristics that were not lost on adding the filler. The performance of the catalytic system was optimized by varying the amount of initiator and adding little proportions of glycerol. The kinetics of the curing process was evaluated by calorimetric measurements. The addition of BN allowed increasing thermal conductivity without loss of mechanical properties like Young modulus, impact resistance, adhesion and other thermal characteristics like Tg or thermal stability. In addition, dielectric properties were improved with the increment of filler.
The influence of N-doping types for carbon nanotube reinforced epoxy composites: A combined experimental study and molecular dynamics simulation Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-09-08 Hana Jung, Hoi Kil Choi, Soyoung Kim, Hun-Su Lee, Yonjig Kim, Jaesang Yu
In this study, nitrogen doped carbon nanotube reinforced epoxy nanocomposites were characterized through experiments and molecular dynamics (MD) simulation. Carbon nanotubes were functionalized by nitrogen inductively coupled plasma. They were made into a nanocomposite by a solvent-free mixing method. The various characteristics of nanocomposites, including nitrogen doped carbon nanotubes were analyzed by the following experiments: a Raman spectra, an X-ray photoelectron spectroscopy (XPS), quasi-static tensile tests, a scanning electron microscopy (SEM), and a transmission electron microscopy (TEM). In addition, an MD simulation was performed to predict the mechanical properties of nanocomposites and the results were compared to the test measurements. It showed that the effective dispersion of nitrogen doped carbon nanotubes was important to improve the mechanical characteristics of the nanocomposites.
Graphene based Strain and Damage Prediction System for Polymer Composites Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-09-08 R. Balaji, M. Sasikumar
Glass fibre reinforced polymer composites are extensively used as an advanced engineering material, particularly in aviation industries because of its superior properties. Unlike metals, damage and failure of the composites are complicated to predict under real-time loading due to its anisotropic nature. With that focus, reduced Graphene Oxide (rGO) based Structural Health Monitoring for polymer composite is proposed in this work. The prioritised aim of this study is to measure the strain induced and the degree of damage accumulated in the composites. To achieve this, the rGO coated glass fibres are embedded into polymer composite to evaluate the strain and damage induced in the composites by measuring the fractional change in the piezoresistance of the coated fibre. The piezoresistive response of the coated fibres showed linear variation under low (elastic) deformation. However, under high (plastic) deformation, the piezoresistance varied nonlinearly with an irregular stepped increment. This nonlinear stepped increment is marked due to the initiation and propagation microcracks in the polymer composites. The damage accumulation in the composite is predicted by measuring the deviation of piezoresistance from the elastic response line using statistical analysis. A statistical correlation is established between the damage accumulation and the experimentally calculated residual strength. The electromechanical study on the rGO coated glass fibres suggested as potential applications for the strain and damage monitoring of composite materials.
Magnetoactive elastomer/PVDF composite film based magnetically controllable actuator with real-time deformation feedback property Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-09-08 Jiabin Feng, Shouhu Xuan, Li Ding, Xinglong Gong
This work reported a high performance flexible magnetically controllable actuator based on magnetoactive elastomer (MAE) and poly (vinylidene fluoride) (PVDF) composite film. The magnetic-mechanic-electric coupling properties of the actuator were systematically investigated by cyclical wrinkle, magnetic bending, and stretching test. The induced charge under a magnetic bending can reach as large as 158 pC even at small magnetic field of 100 mT with the bending angle up to almost 90 degrees within 0.6 s. Moreover, a new model was proposed to theoretically reveal the intrinsic correspondence. The model matches well with the experimental results. Based on this kind of actuator, a magnetically controllable tentacle is developed, which could grasp, transport, and release object by switching the supplied current. Due to the real-time deformation feedback characteristics, this kind of actuators can find wide applications in actively controllable engineering, artificial robotics, and biomedicine.
A fast water-induced shape memory polymer based on hydroxyethyl cellulose/graphene oxide composites Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-09-07 Yongkang Bai, Xin Chen
Environmentally Assisted Crack Growth in Adhesively Bonded Composite Joints Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-08-26 Jared Tracy, Yikai Yin, Jeffrey Yang, John C. Osborne, Kay Y. Blohowiak, Reinhold Dauskardt
Adhesively bonding composite components is a reliable alternative to conventional joining processes that minimizes part weight and reduces fabrication costs. Regarding performance and reliability, of particular interest is developing adherend surface treatments that enhance adhesion of the joint interfaces in aggressive chemical environments. Using fracture mechanics-based adhesion metrologies, critical and subcritical crack growth were evaluated for several peel- ply-treated, adhesively bonded composite joints. Fracture toughness, Gc, and corresponding failure modes were evaluated for specimens constructed using two different bonding processes (co-bonding and secondary bonding) and four different peel ply treatments. Environmentally assisted crack growth was evaluated as a function of time in several environments: humid, high temperature humid, and hydraulic fluid immersion. It is shown that humid environments accelerate crack growth rates, da/dt, relative to the strain energy release rate, G. This effect was amplified at elevated temperatures and further amplified in the presence of hydraulic fluid.
Fabrication of high quality composite laminates by pressurized and heated-VARTM Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-08-22 M. Akif Yalcinkaya, E. Murat Sozer, M. Cengiz Altan
Although vacuum-assisted transfer molding (VARTM) is preferred for manufacturing medium to large composite parts due to its simple tooling and low cost, part quality dictated by dimensional tolerances, void content and mechanical properties is usually low due to inherent limitations of the process. In this study, the conventional VARTM process was modified by external pressurization of a heated mold to increase fiber volume fraction and improve mechanical properties of laminates. During post-filling, various levels of external pressure were applied in a pressure chamber mounted on top of the mold. It was observed that pressurized VARTM led to laminates with less than 1% void content. In addition, fiber volume fraction and flexural strength were increased 25% and 13% with respect to non-pressurized VARTM, respectively which demonstrates the potential for manufacturing considerably higher quality composites by pressurized VARTM.
Highly aligned graphene oxide/poly(vinyl alcohol) nanocomposite fibers with high-strength, antiultraviolet and antibacterial properties Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-08-15 Xinjun Hu, Nan Ren, Yuanzhi Chao, Huilin Lan, Xiaojie Yan, Yan Sha, Xiaolin Sha, Yongxiao Bai
Demands for the strong and multifunctional fiber has substantially increased in textile industry, biomedical, and biotechnological applications. This study explores to fabricate nanocomposite functional fibers by embedding highly oriented graphene oxide (GO) into the poly (vinyl alcohol) (PVA) matrix. The GO/ PVA nanocomposite fibers were prepared via gel spinning and subsequent hot drawing process. The tensile strength of the produced GO/PVA nanocomposite fibers was significantly enhanced owing to the uniformly dispersed and oriented GO nanosheets. Additionally, the ultraviolet protection factor of the highly aligned GO/PVA nanocomposite fibers is about 16 times than that of the neat PVA fiber. The as-prepared GO/PVA nanocomposite fibers also exhibit significant activity against both Gram-negative and Gram-positive bacteria. This highly aligned and integrated approach suggests an effective method to prepare graphene-based nanocomposites fibers with high performances and novel functional characteristics.
The effect of multi-wall carbon nanotube morphology on electrical and mechanical properties of polyurethane nanocomposites Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-08-14 Jatin Sethi, Essi Sarlin, Seyyed Shayan Meysami, Reija Suihkonen, Arunjunai Raja Shankar Santha Kumar, Mari Honkanen, Pasi Keinänen, Nicole Grobert, Jyrki Vuorinen
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