Mechanical behaviour of plain-knit reinforced injected composites: Effect of inlay yarns and fibre type

This paper investigates the effect of inlay yarns and fibre type (E-glass, basalt, carbon) to improve the mechanical behaviour of plain knit reinforced composites (epoxy matrix). The tensile behaviour of the dry reinforcement was investigated in the wale and course-directions and has shown that the course-wise deformation is drastically reduced whereas the strength is strongly increased when inlay yarns are included. Fibre type has a weak effect on deformation and strength. For the composite material, processed by Liquid Composite Moulding, the carbon fibre reinforcement gives always the best results whatever the testing direction. Inlay yarns decrease the 0° mechanical properties, whereas 45° and 90° are increased. Moreover a quasi-isotropic behaviour is obtained when using two inlay yarns, irrespective of the fibre types.     

Additive manufacturing of carbon fiber reinforced thermoplastic composites using fused deposition modeling

Additive manufacturing (AM) technologies have been successfully applied in various applications. Fused deposition modeling (FDM), one of the most popular AM techniques, is the most widely used method for fabricating thermoplastic parts those are mainly used as rapid prototypes for functional testing with advantages of low cost, minimal wastage, and ease of material change. Due to the intrinsically limited mechanical properties of pure thermoplastic materials, there is a critical need to improve mechanical properties for FDM-fabricated pure thermoplastic parts. One of the possible methods is adding reinforced materials (such as carbon fibers) into plastic materials to form thermoplastic matrix carbon fiber reinforced plastic (CFRP) composites those could be directly used in the actual application areas, such as aerospace, automotive, and wind energy. This paper is going to present FDM of thermoplastic matrix CFRP composites and test if adding carbon fiber (different content and length) can improve the mechanical properties of FDM-fabricated parts. The CFRP feedstock filaments were fabricated from plastic pellets and carbon fiber powders for FDM process. After FDM fabrication, effects on the tensile properties (including tensile strength, Young's modulus, toughness, yield strength, and ductility) and flexural properties (including flexural stress, flexural modulus, flexural toughness, and flexural yield strength) of specimens were experimentally investigated. In order to explore the parts fracture reasons during tensile and flexural tests, fracture interface of CFRP composite specimens after tensile testing and flexural testing was observed and analyzed using SEM micrograph.     

Study on the mechanical properties and thermal properties of jute and banana fiber reinforced epoxy hybrid composites

The aim of the present study is to investigate and compare the mechanical and thermal properties of raw jute and banana fiber reinforced epoxy hybrid composites. To improve the mechanical properties, jute fiber was hybridized with banana fiber. The jute and banana fibers were prepared with various weight ratios (100/0, 75/25, 50/50, 25/75 and 0/100) and then incorporated into the epoxy matrix by moulding technique to form composites. The tensile, flexural, impact, thermal and water absorption tests were carried out using hybrid composite samples. This study shows that addition of banana fiber in jute/epoxy composites of up to 50% by weight results in increasing the mechanical and thermal properties and decreasing the moisture absorption property. Morphological analysis was carried out to observe fracture behavior and fiber pull-out of the samples using scanning electron microscope.     

Enhancing damping features of advanced polymer composites by micromechanical hybridization

A hybrid configuration at the micromechanical level is presented and described as a suitable approach to enhance the damping features of advanced polymer composites. A micro-level hybridization was achieved on dry preform reinforcements by embedding visco-elastic fibres within standard carbon tows. Unidirectional composites with two viscoelastic volume fractions (2.5% and 5% vol/vol) were manufactured by a vacuum infusion process and later tested by dynamic mechanical analysis along the principal directions. Final results reveal a significant enhancement (+80% and +56%) of the damping properties, respectively, for the longitudinal and the transverse directions in the case of the highest viscoelastic fibre content.In turn, the elastic properties of the final composite were greatly reduced (−37% and −35%) with respect to the standard composite. Final results support further work in the direction of micromechanical hybridization looking at the potential exploitation of standard textile configurations with different viscoelastic fibre content to enhance damping properties.     

The voids formation mechanisms and their effects on the mechanical properties of flax fiber reinforced epoxy composites

Unidirectional flax fiber reinforced composites (FFRC) were made by hot press. Effects of processing parameters, including curing pressure, time and temperature on the distribution, shape and content of the voids formed during the manufacturing process of FFRC were investigated. The voids were characterized with the aid of ultrasonic C-scan and optical microscopy. Tensile and interlaminar shear properties of FFRC containing different content and shape of the voids were tested. The results showed that the voids were easily trapped in both the intralaminar and inside the flax yarns of FFRC due to the distinct structural characteristics of flax fibers. The relationships between voids and mechanical properties of the composites were established.     

Characterization of thermoplastic natural fibre composites made from woven hybrid yarn prepregs with different weave pattern

This paper focuses on the effect of weave structure on mechanical behaviour and moisture absorption of the PLA/hemp woven fabric composites made by compression moulding. The unidirectional woven fabric prepregs were made from PLA (warp) and PLA/hemp wrapped-spun hybrid yarn (weft) with two different weave patterns; 8-harness satin and basket. Unidirectional composites with 30 mass% hemp content were fabricated from these prepregs, and compared to winded PLA/hemp hybrid yarn laminates with same composition. The composite from the satin fabric had significantly lowest porosities and best mechanical properties compared to the composite made from the winded hybrid yarn and basket fabric. The tensile, flexural, and impact strength were 88 MPa, 113.64 MPa, and 24.24 kJ/m², respectively. The effect of weave pattern on water absorption is significant. Although the composite from hybrid yarn laminate has larger water absorption than that of the pure PLA, it exhibits lower moisture absorption than both weaves.     

The importance of bonding in intralayer carbon fibre/self-reinforced polypropylene hybrid composites

Polymer composites are usually either stiff or tough, but seldom both. Intralayer hybrids of carbon fibre and self-reinforced polypropylene (PP) do offer the potential to achieve a unique combination of toughness and stiffness. In these hybrids, the bonding between carbon fibre prepregs and PP tapes is a crucial parameter. For a weak bonding, the 20% ultimate tensile failure strain and high penetration impact resistance of self-reinforced PP were maintained. For a strong bonding, the ultimate tensile failure strain was strongly reduced, but the flexural performance was improved. For a homopolymer PP matrix in the prepregs, the weak bonding between fibre and matrix caused the penetration impact resistance to reduce according to a linear rule-of-mixtures. For a maleic anhydride modified PP matrix however, the strong fibre–matrix bonding greatly reduced the penetration impact resistance. These results provide new insights into designing hybrid composites with a unique balance of stiffness and failure strain.     

An investigation on shape memory behaviours of hydro-epoxy/glass fibre composites

Shape-memory polymers (SMPs) have the capacity to return large strains by external stimuli. Among various SMPs, shape-memory epoxy has received considerable attention because of its superior mechanical and thermal properties as well as excellent shape-memory performance. In this study, short glass fibre-reinforced shape-memory hydro-epoxy composites are developed to improve further the mechanical property of shape-memory epoxy resin. The thermomechanical and shape-memory properties of the developed composite materials are investigated by dynamic mechanical analysis, bend test and shape recovery test. The results indicate that the glass modulus and bend strength of the developed composite materials initially increase and then slightly decrease with increasing short glass fibre content. The glass transition temperature of the developed composite materials does not change with increasing short glass fibre. When the short glass fibre content is less than 4.5 wt.%, full recovery can be observed after only several minutes at different temperatures. The shape-memory property of the composite materials is not affected greatly. However, when the short glass fibre content is more than 4.5 wt.%, the material would be destroyed after deformation.     

A short review on basalt fiber reinforced polymer composites

A recent increase in the use of ecofriendly, natural fibers as reinforcement for the fabrication of lightweight, low cost polymer composites can be seen globally. One such material of interest currently being extensively used is basalt fiber, which is cost-effective and offers exceptional properties over glass fibers. The prominent advantages of these composites include high specific mechano-physico-chemical properties, biodegradability, and non-abrasive qualities to name a few. This article presents a short review on basalt fibers used as a reinforcement material for composites and discusses them as an alternative to the use of glass fibers. The paper also discusses the basics of basalt chemistry and its classification. Apart from this, an attempt to showcase the increasing trend in research publications and activity in the area of basalt fibers is also covered. Further sections discuss the improvement in mechanical, thermal and chemical resistant properties achieved for applications in specific industries.     

Interstrand void content evolution in compression moulding of randomly oriented strands (ROS) of thermoplastic composites

Compression moulding of randomly oriented strands (ROS) of thermoplastic composite is a process that enables the forming of complex shapes with keeping final properties close to that of continuous fibre composites. During forming several deformation mechanisms occur. In this paper we focus on the interstrand void content (ISVC) reduction: the squeezing of each single strand during compression enables filling of the gaps between strands. A modelling of this deformation mechanism was developed. The compaction is ruled by an ordinary differential equation that was solved numerically. The model was validated experimentally using an instrumented hot press with Carbon-PEEK prepreg strands. The model accurately predicted ISVC in four characteristic cases. Using the proposed model, the influence of several process and material parameters were investigated. Finally, a design chart giving the final ISVC for a wide range of pressure, strand geometry and part thickness, was constructed.     

Characterization of organo-montmorillonite (OMMT) modified wood flour and properties of its composites with poly(lactic acid)

In this research, sodium-montmorillonite (Na-MMT) at four different concentrations (0.5%, 1.0%, 2.0% and 4.0%) and didecyl dimethyl ammonium chloride (DDAC) were used to modify wood flour (WF) in a two-step process to form organo-montmorillonite (OMMT) inside the WF. Then the WFs with three sizes were mixed with poly(lactic acid) (PLA) to produce WF/PLA composites. The treated WF was characterized and some physical and mechanical properties of the composites were tested. The results showed that: (1) Na-MMT was successfully transformed to OMMT and uniformly distributed inside WF; (2) at 0.5% MMT concentration, water repellency, flexural and tensile properties of the composites were improved significantly. However, after introducing more OMMT, the enhancements diminished because of poor interfacial adhesion caused by OMMT agglomeration; (3) the composites with the maximum size of WF showed the most significant improvements among all, suggesting bigger WF was more suitable for this modification process.     

Manufacture and characterisation of thermoplastic composites made from PLA/hemp co-wrapped hybrid yarn prepregs

PLA/hemp co-wrapped hybrid yarns were produced by wrapping PLA filaments around a core composed of a 400 twists/m and 25 tex hemp yarn (Cannabis sativa L) and 18 tex PLA filaments. The hemp content varied between 10 and 45 mass%, and the PLA wrapping density around the core was 150 and 250 turns/m. Composites were fabricated by compression moulding of 0/90 bidirectional prepregs, and characterised regarding porosity, mechanical strength and thermal properties by dynamic mechanical thermal analysis (DMTA) and differential scanning calorimetry (DSC). Mechanical tests showed that the tensile and flexural strengths of the composites markedly increased with the fibre content, reaching 59.3 and 124.2 MPa when reinforced with 45 mass% fibre, which is approximately 2 and 3.3 times higher compared to neat PLA. Impact strength of the composites decreased initially up to 10 mass% fibre; while higher fibre loading (up to 45 mass%) caused an increase in impact strength up to 26.3 kJ/m², an improvement of about 2 times higher compared to neat PLA. The composites made from the hybrid yarn with a wrapping density of 250 turns/m showed improvements in mechanical properties, due to the lower porosity. The fractured surfaces were investigated by scanning electron microscopy to study the fibre/matrix interface.     

Effect of basalt fibre hybridisation on post-impact mechanical behaviour of hemp fibre reinforced composites

A major limitation to the spreading of natural fibre reinforced composites in semi-structural components is their unsatisfactory impact performance. As a potential solution, the production of synthetic/plant fibre hybrid laminates has been explored, trying to obtain materials with sufficient impact properties, while retaining a reduced cost and a substantial environmental gain. This study explores the effects of hybridisation of basalt fibre on post-impact behaviour and damage tolerance capability of hemp fibre reinforced composites. All reinforced laminates were impacted in a range of energies (3, 6, and 9 J) and subjected to both quasi-static and cyclic flexural tests with a step loading procedure. The tests have also been monitored by acoustic emission (AE), which has confirmed the existence of severe limitations to the use of natural fibre reinforced composites even when impacted at energies not so close to penetration and the enhanced damage tolerance offered by the hybridisation with basalt fibers.     

A rate-dependent non-orthogonal constitutive model for describing shear behaviour of woven reinforced thermoplastic composites

A rate dependent constitutive model for woven reinforced thermoplastic matrix composites at forming temperatures is proposed in this work. The model is formulated using a stress objective derivative based on the fibre rotation. Nonlinear shear behaviour is modelled as a polynomial function and the rate dependence is described using a Cowper–Symonds overstress law formulated in terms of shear angle rate. The model parameters are determined by means of bias extension tests. The applicability of the material model is validated through a forming experiment.     

Influence of electroless nickel-plating on fracture toughness of pitch-based carbon fibre reinforced composites

Nickel-Pitch-based carbon fibres (Ni-PFs) were prepared by electroless nickel-plating to enhance fracture toughness of Ni-PFs reinforced epoxy matrix composites (Ni-PFs/epoxy). The surface properties of Ni-PFs were determined by scanning electron microscopy (SEM), X-ray photoelectron spectrometry (XPS), and X-ray diffraction (XRD). The fracture toughness of the Ni-PFs/epoxy was assessed by critical stress intensity factor (K_IC) and critical strain energy release rate (G_IC). The fracture toughness of Ni-PFs/epoxy was enhanced compared to those of PFs/epoxy. These results were attributed to the increase of the degree of adhesion at interfaces between Ni-PFs and matrix resins in the composites.     

Experimental and theoretical studies on the properties of injection moulded glass fibre reinforced mixed plastics composites

Recycled mixed post-consumer and post-industrial plastic wastes consisting of HDPE, LDPE and PP were injection moulded with short glass fibre (10–30% by weight) to produce a new generation composite materials. Intensive experimental studies were then performed to characterise the tensile, compression and flexural properties of glass fibre reinforced mixed plastics composites. With the addition of 30 wt.% of glass fibre, the strength properties and elastic modulus increased by as much as 141% and 357%, respectively. The best improvement is seen in the flexural properties due to the better orientation of the glass fibres in the longitudinal direction at the outer layers. The randomness and length of the glass fibre were accounted to modify the existing rule of mixture and fibre model analysis to reliably predict the elastic and strength properties of glass fibre reinforced mixed plastics composites.     

Penetration impact testing of self-reinforced composites

Penetration impact resistance is one of the key advantages of self-reinforced composites. This is typically measured using the same setup as for brittle fibre composites. However, issues with the test configuration for falling weight impact tests are reported. Similar issues have been found in literature for other composites incorporating ductile fibres. If the dimensions of the test samples are too small relative to the clamping device, then the test samples can heavily deform by wrinkling and necking. These unwanted mechanisms should be avoided as they absorb additional energy compared to properly tested samples. Furthermore, these mechanisms are found to occur more easily at lower compaction temperatures due to the lower interlayer bonding. In conclusions, the sample dimensions of ductile fibre composites should be carefully selected for penetration impact testing. If wrinkling or necking is observed, then the sample dimensions need to be increased.     

Experimental study of defect formation during processing of randomly-oriented strand carbon/PEEK composites

An investigation of the moulding defects formed during compression moulding of randomly-oriented strand carbon/PEEK composites is presented. The cause of defect formation was identified as non-uniform shrinkage due to a high coefficient of thermal expansion at the onset of crystallization. Panels with void content ranging from 0% to 1.3% were moulded by releasing the moulding pressure at specific temperatures during the cooling process. Mechanical tests showed a reduction in specimen compressive strength from 15% to 25% for a void content of 0.63–1.3%. It was concluded that the high concentration of porosity near the surface of the panels was the likely cause of the strength reduction.     

A displacement-detection based approach for process monitoring and processing window definition of resistance welding of thermoplastic composites

The evolution of weld displacement, or the thickness of welding stack, with welding time during resistance welding of thermoplastic composites was characterised, and based on this the possibility of using displacement data for process monitoring and processing window definition was investigated. Resistance welding of glass fabric reinforced polyetherimide using a metal mesh as the heating element was studied, and weld displacement was detected using a laser sensor. The effect of welding parameters on the displacement curve was studied. Welding defects, such as voids and squeeze flow, could be detected by monitoring the weld displacement. Fast definition of the welding processing window was found to be possible using displacement curves, and the predicted processing window showed good agreement with the processing window determined from mechanical tests.     

Correlation between electrical conductivity and manufacturing processes of nanofilled carbon fiber reinforced composites

This paper describes the difference on the electrical performance of carbon fiber reinforced composites (CFRCs) when two different Resin Film Infusion (RFI) manufacturing techniques are used. For the panel obtained by bulk infusion the measured in plane and out of plane electrical conductivities were 2.0 × 10⁴ S/m and 3.9 S/m respectively and for the panel prepared using the traditional resin film infusion the values were 1.1 × 10⁴ S/m and 1.7 S/m respectively. Morphological investigations on the sections of etched panels have highlighted that this difference in the electrical conductivity was strictly related to the different distribution of multiwall carbon nanotubes (MWCNTs) between the carbon fibers (CFs) of the plies.