Journal of Composite Materials

In this article, a detailed systematic methodology to fabricate and characterize the diverse properties of soy protein and sisal fiber reinforced green composites has been presented. After fabrication by hand lay-up and solution casting method, these composites with varying sisal fiber weight percentages (0, 3, 4, 5, 6, 7 and 10) were put to various characterization tests. The surfaces of sisal fiber were treated with sodium hydroxide to enhance its interfacial bonding properties. The fabricated samples were examined on the basis of microstructural tests that included the scanning electron microscopy; followed by the mechanical (tensile) and physical (water absorption) tests. Finally, the thermal tests were performed that involved the thermogravimetric analysis, differential thermal analysis and dynamic mechanical analysis tests. The phytagel modified soy protein-based composite with 5 wt.% of sisal fiber content was confirmed to be the best of all compositions under this scrutiny, which was authenticated by the micro-structural and mechanical tests. To further enhance the mechanical, physical and thermal properties of fabricated composites, chitosan coating was applied on them.

A numerical model was developed to predict the defect formation during processing of compression moulded discontinuous long fibre carbon/polyether ether ketone composites. The model inputs are the material's temperature-dependant properties (through-thickness modulus and thermal shrinkage), the temperature distribution of the part during cooling and the applied moulding pressure. The material properties of carbon/polyether ether ketone prepreg were measured during cooling from melt using thermal analyses. The model was employed to identify regions on manufactured panels where pressure could be lost during cooling, which are prone to defect formation. Validation was performed by comparing the predicted defect areas against those found on flat panels moulded at pressures ranging from 10 to 110 bar. The model was then employed in a case study to show the importance of the cooling strategy in order to prevent defects on complex-shape components.

Effect of distributed defects on effective material properties of composites is required for the progressive failure models. Although the degradation of the effective material properties due to the presence of the lower scale damages is well investigated, how each material coefficient should be compromised in a progressive failure model is still a dilemma. Percentage of defects, the shape of the defects and their stochastic distribution may affect the individual material coefficients in a unique way and may not be uniform across the constitutive matrix. Hence, to find how the individual material coefficients in a constitutive matrix changes due to the presence of the voids and fiber breakage, all material coefficients in a constitutive matrix were studied herein. Representative volume element of a unidirectional fiber-matrix composite was studied with appropriate boundary conditions and respective material coefficients were calculated. It was found that the local gradients of the degradation curve obtained for each material coefficient are not linear with the increasing percentage of degradation and not uniform for all material coefficients. The shape and different locations of the defects with constant defect percentage were found to be inert towards affecting the material coefficients.

The goal of the present study is to fabricate the short fiber-reinforced metal matrix composites by accumulative roll bonding. Various mixtures of fibers including 100 glass, 95 glass/5 carbon and 80 glass/20 carbon (all in wt.%) were used as the reinforcement. In order to investigate the bonding quality at layer interface, the composites with various fiber mixtures were produced by cold roll bonding. The bonding strength of the composites under different processing conditions including the fiber mixture, reduction in thickness and post-rolling annealing was measured by the peeling test. The 95 glass/5 carbon mixture was used to fabricate the fiber-reinforced composite through accumulative roll bonding. The fiber distribution, tensile properties and wear behavior of the composite were investigated at various numbers of accumulative roll bonding cycle. It was found that during accumulative roll bonding, the fiber clusters were broken and fragmented into smaller pieces. Results showed that the tensile strength and wear resistance of the composite enhanced with increasing the number of accumulative roll bonding cycles.

The aim of the present study is to investigate the effect of SiC-graphite reinforcement on the properties of pure copper. Copper matrix composites with SiC-graphite reinforcement (0, 2.5,5, 7.5 and 10 wt.%) were prepared by stir casting process. Microstructure, phase, density, hardness and wear rate of prepared samples have been investigated. X-ray diffraction revealed that there is no intermediate phase formation between the reinforcement and matrix as a result of interfacial bonding between them. Microstructure study shows the uniform distribution of SiC-graphite particles in the Cu-matrix. Mechanical and corrosion properties of these Cu matrix MMCs were found to be dependent on the reinforcement content. Hardness was found to decrease with the addition of graphite due to its soft nature. Composite containing 5 wt.% reinforcement has shown minimum wear rate and maximum corrosion resistance. It is expected that the present composite will be useful for thermal management applications especially in heat exchangers.

This research paper presents the results of an experimental investigation on the axial compressive behaviour of 24 geopolymer concrete-filled glass fibre-reinforced polymer tubes. The test variables considered are the compressive strength of geopolymer concrete (30 MPa and 35 MPa) and the shape of the cross section (square, circular and rectangular). All the glass fibre-reinforced polymer tubes had the same amount of fibres and similar fibre orientation together with the same aspect ratio. The failure of the square and rectangular columns initiated with the splitting of the corners and resulted in a lower load-carrying capacity compared to the circular columns whose failure was initiated by the crushing of glass fibre-reinforced polymer tube followed by the separation of glass fibre-reinforced polymer tube into strips. It can be concluded that axial load-carrying capacity of square and rectangular sections can be improved by a concrete filler with higher compressive strength. Adopted finite element analysis to simulate the behaviour of the columns is capable of predicting the stress–strain behaviour and the mode of failure.

Anisotropic properties can be imparted to composite materials by arranging filler particles along specific directions inside the polymer matrix. These anisotropic patterns can be produced through dynamic field-assisted assembly of the filler particles during additive manufacturing. Using finite element analysis, we explore how chainlike arrangements of nickel particles embedded in a polydimethylsiloxane matrix modify bulk thermal conductivities in the axial and transverse directions. The axial conductivity increases up to nine times of the matrix conductivity with increasing filler volume fraction. While the axial conductivity decreases with increasing interparticle spacing, the transverse conductivity is uninfluenced. When particles within a chain are arranged in a zigzag pattern, increasing the interparticle zigzag angle decreases axial conductivity but increases transverse conductivity. As that angle increases to ∼55 º, the axial conductivity approaches a minimum, while the transverse conductivity approaches its maximum. An empirical model that includes effects of interparticle spacing and zigzag angle to predict the anisotropic thermal conductivity of a composite containing particle chains is presented. These results are relevant for the material design of particulate-reinforced polymer composites for advanced field-assisted additive manufacturing strategies.

The combination of thin light metal sheets with fibre-reinforced thermoplastic layers in multi-layered fibre-metal-laminates advantageously combines the properties of both material classes. In this way, components can be developed which have both significantly increased specific properties (strength and stiffness with respect to density) and high energy absorption capacity compared with conventional design with mono materials. However, the structural behaviour of crash structures is decisively determined by material behaviour of the thermoplastic and metal constituents as well as the interface properties between both constituents and the corresponding delamination behaviour. To evaluate the structural response of multi-layered fibre-metal-laminates under highly dynamic loading conditions, Charpy tests were performed, where the test parameters, light metal material configuration, support length and laminate thickness, were varied. Moreover, the metal sheet surfaces were pre-treated by embossing to achieve different surface topologies. The influence of the different test parameters on the specific energy absorption capacity was characterised by the analysis of force–displacement curves.

This work is intended to characterize the mechanical behavior of hybrid carbon–glass composite plates under combined loading of bending and torsion, and to determine the optimal ply fiber orientations to minimize the maximum out-of-plane displacement under such loading conditions. Hybrid composite plates were manufactured with 10 plies each and different stacking sequences using hand lay-up, with carbon fiber and glass fiber reinforcements in an epoxy matrix. Two experimental setups (involving two distinct boundary conditions) are here considered to test the composite plates, both simulating combined loading of bending and torsion. Numerical simulations of the experimental tests were performed in ABAQUS® and validated with the experimental data. Using the ply fiber orientations as design variables, the hybrid composite plates were then optimized using global and local optimization using direct search (GLODS). The objective function of minimization of the maximum out-of-plane displacement is carried out through an interactive cycle between GLODS and ABAQUS®. Specimens of three optimized laminates were also manufactured for experimental validation. The optimization process contributed to improve the performance of the hybrid composite plates in more than 30% when compared to some non-optimized plates.

Due to environmental challenges and need for action with regard to CO₂ emission, reducing the weight of vehicles has become one of the most important goals of car manufacturers in Europe. Materials like fibre-reinforced plastics and aluminium are the core of the research for lightweight design. However, efficiently joining these materials together is still a challenge. When thermoplastic composites are used, direct joining (i.e. without adhesives or fasteners) with the metal substrate can be obtained using welding technologies which melt the thermoplastic at the interface. In this study, ultrasonic plastic welding was investigated as a candidate technology for joining aluminium and carbon fibre-reinforced thermoplastics. The goal was to understand the main mechanisms involved in the welding process and how they affect the performance of the joint. Initially, the technique proved to be successful, but moderate strengths were obtained. Therefore, several surface pre-treatments of aluminium were analysed to improve the performance in terms of lap shear strength; mechanical, chemical and physical treatments were also carried out. With laser structuring, strengths comparable to adhesive bonded joints were obtained, but in a much shorter process time. Other treatments led to considerable improvements as well. The encouraging results achieved represent an important step in the development of ultrasonic plastic welding for multi-material joining in the automotive industry.

In this paper, the static and fatigue behavior of flax fiber-reinforced composites with and without an interleaved natural viscoelastic layer are investigated. Viscoelastic composite plates consist of a soft natural viscoelastic layer which is confined between two identical flax fiber reinforced composites. Different stacking sequences of specimens are tested with uniaxial tensile loading until failure. The mechanical behavior and the acoustic activity of damage sources in various configurations with and without a viscoelastic layer are compared. The analysis of acoustic emission signals and the macroscopic and microscopic observations led to the identification of the main acoustic signatures of different damage modes dominant in each type of composites (with and without a viscoelastic layer). These results allow better identification of the influence of the impact of a viscoelastic layer on the mechanical behavior of different composites. In addition, static and fatigue flexural behavior of unidirectional composites with and without viscoelastic layer are characterized in 3-point bending tests. The effects of viscoelastic layer on the stiffness, hysteresis loops, and loss factor are studied for various numbers of cycles during cyclic fatigue.