The abrasive wear of short fibre composites

The wear rate and the friction coefficient of short fibre composites (carbon fibre- or glass fibre-reinforced plastics) made by injection moulding are measured and the microstructures are examined by scanning electron microscopy. The wear rate is found to be a function of abrasive particle size and the fibre orientation with respect to the sliding direction. The friction coefficient varies with abrasive particle size due to a ploughing action. The evidence of the lateral flaking mechanism due to the crack generation/propagation effect is presented. A new, theoretical wear equation is derived from the combination of flaking theory and fracture mechanics concepts which is an extension of two previous semi-empirical expressions.     

Fatigue behaviour of continuous glass fibre reinforced composites

A study has been undertaken of fatigue in glass fibre reinforced composites. Two matrix resins were tested: a standard polyester and a polyurethane-vinyl-ester, which was designed to have a higher toughness. Three different types of glass fibre fabrics were used for reinforcement: a conventional woven roving and two stitch-bonded cloths. The glass cloths were combined into various lay-ups, in order to consider the effects of matrix, cloth and lay-up on the fatigue strength. Additionally, a study was undertaken to evaluate the micromechanisms that occurred during fatigue and how damage accumulated throughout the sample lifetime. This involved measuring stiffness changes during fatigue cycling, followed by microscopic study of the samples. It was found that similar damage micromechanisms occurred in each lay-up regardless of resin and cloth type, and these included matrix cracking, delamination and fibre breakage. However, differences were observed in the extent, location and rate of damage, and these were consistent with the variations seen in the fatigue strengths.     

Influence of fillers on abrasive wear of short glass fibre reinforced polyamide composites

Various composites of polyamide 6 filled with short glass fibre, polytetrafluoroethylene and metal powders viz. copper and bronze were formulated in the laboratory and characterised for their various mechanical properties such as tensile strength, tensile elongation, flexural strength, hardness and impact strength. Compositional analysis was done with gravimetry, solvent extraction and differential scanning calorimetry (DSC) techniques followed by tribo-performance evaluation in abrasive wear mode by abrading a sample against silicon carbide (SiC) abrasive paper in a single pass condition under various loads. It was observed that the fibre reinforcement deteriorated the abrasive wear resistance of virgin polymer. Combination of fibre and particulate filler was more detrimental in this respect. Efforts were made to correlate the wear performance with the appropriate mechanical properties. Under selected loading condition, wear as a function of product of hardness, elongation to break (e) and ultimate tensile strength (S) showed better correlation than Ranter-Lancaster plot. Scanning electron microscopy (SEM) was used to analyse the worn surfaces of the samples.     

Three-body abrasive wear behaviour of carbon and glass fiber reinforced epoxy composites

Three-body abrasive wear behaviour of carbon–epoxy (C–E) and glass–epoxy (G–E) composites has been investigated. The effect of abrading distance, viz., 270, 540, 810 and 1080 m and different loads of 22 and 32 N at 200 rpm have been studied. The wear volume loss and specific wear rate as a function of load and abrading distance were determined. The wear volume loss increases with increasing load/abrading distance. However, the specific wear rate decreases with increase in abrading distance and increases with the load. However, C–E composite showed better abrasion wear resistance compared to G–E composite. The worn surface features have been examined using scanning electron microscope (SEM). SEM micrographs of abraded composite specimens revealed the high percentage of broken glass fiber compared to carbon fiber and also better interfacial adhesion between epoxy and carbon fiber.     

Influence of fibre orientation on three-body abrasive wear behaviour of unidirectional carbon fibre-reinforced polyetherimide composite

Three-body abrasive wear behaviour of neat polyetherimide (PEI) and unidirectional carbon fibre-reinforced PEI (CF/PEI) has been studied using a rubber wheel abrasion test rig. The abrasive wear studies were carried out at different loads (5–20 N) at a constant sliding velocity (v = 2.4 m/s) of rubber wheel. The influence of fibre orientation, i.e. parallel (P-fibre orientation) and anti-parallel (AP-fibre orientation) on wear rate of CF/PEI composite has also been studied. The results showed that the fibre orientation has a significant influence on the three-body abrasive wear behaviour of CF/PEI. The abrasive wear rate was higher when fibres are oriented at anti-parallel than that of parallel orientation of fibres. The worn surfaces have been observed using scanning electron microscope to understand the possible wear mechanisms involved during material removal processes.     

Friction and wear behaviour of continuous fibre as cast Kevlar-phenolic resin composite

A compression moulded Kevlar-phenolic resin composite consisting of 30 wt% continuous fibres was slid against a steel disc such that the fibre axis was normal to the sliding plane. The sliding experiments were conducted in a normal pressure range of 0.47–4.27 MPa and at a sliding speed of 0.5 ms^–1. The initial sliding interaction is abrasive. With further sliding, as patches of polymer transfer film develop on the polymer pin and counterface, the interaction becomes adhesive and steady-state friction is established. The wear resistance of the polymer was found to be related to the stability of this film.     

Mathematical model for tensile behaviour of hybrid continuous fibre cement composites

A mathematical model has been developed for the tensile behaviour of cement composites reinforced with two types of continuous and unidirectional aligned fibres. The model is based on the theory for single fibre composites proposed by Aveston, Cooper and Kelly. Theoretical curves have been obtained for the tensile properties of the polypropylene/glass fibre-reinforced cement composites by means of substituting parameters into the developed equations, and these curves were compared with experimental results for a limited range of fibre combinations. It is shown that to attain optimum hybrid effects for toughness and the first maximum point of the stress-strain curve, the correct fibre volume combinations should be included.     

Influence of graphite filler on two-body abrasive wear behaviour of carbon fabric reinforced epoxy composites

The influence of graphite filler additions on two-body abrasive wear behaviour of compression moulded carbon–epoxy (C–E) composites have been evaluated using reciprocating wear unit and pin-on-disc wear unit under single pass and multi-pass conditions respectively. The carbon fabric used in the present study is a plain one; each warp fiber pass alternately under and over each weft fiber. The fabric is symmetrical, with good stability and reasonable porosity. Abrasive wear studies were carried out under different loads/abrading distance using different grades of SiC abrasive paper (150 and 320 grit size). Graphite filler in C–E reduced the specific wear rate. Further, the wear volume loss drops significantly with increase in graphite content. Comparative wear performance of all the composites showed higher specific wear rate in two-body wear (single-pass conditions) compared to multi-pass conditions. Further, the tribo-performance of C–E indicated that the graphite filler inclusion resulted in enhancement of wear behaviour significantly. Wear mechanisms were suggested and strongly supported by worn surface morphology using scanning electron microscopy.     

Deformation and fracture behaviour of flax fibre reinforced thermosetting polymer matrix composites

The mechanical properties of unidirectional flax fibre reinforced unsaturated polyester resin composites were studied with particular emphasis on their tensile deformation behaviour. These materials displayed characteristic non-linear behaviour when loaded parallel to the axis of the fibre, with a distinct knee preceding a drop in stiffness. Further deformation resulted in strain hardening behaviour. Load cycling and acoustic emissions analysis were used to investigate the nature of the knee and it was found that this corresponded with yielding behaviour in the composite. A well-defined yield point could be identified, which in composites of around 60% fibre volume fraction, occurred at a strain of some 0.12% and a tensile stress of 32 MPa. Varying the interfacial properties, through chemical modification of the fibre prior to lamination, was found to have a marked effect upon the onset of yielding and the yield point itself, as well as the deformation and fracture behaviour of the laminate. It is considered that this behaviour is intimately linked to the straining behaviour of the fibre as well as the fibre–matrix interaction and hypotheses to explain the observed behaviour are presented.     

Fatigue of continuous fibre composites

Fatigue curves for composites are derived from those of the components, with as little arbitrariness as possible. Even with this restriction, the expected fatigue behaviour of the composites turns out to be of a rather diverse nature, depending on modulus ratio, volume fraction, and residual stress. The results concern pulsating tension as well as fluctuating load at an arbitrary mean stress. By comparison with available experimental data, our results lead to a better understanding of composite behaviour.     

The wear resistance of glass fibre reinforced epoxy composites

Polymers are usually characterized by low moduli and strength. Epoxy, as a thermoset material, has a low wear resistance. Additions of glass fibres improve the elastic modulus and tensile strength and can improve the wear resistance. The composites were prepared by pultrusion of the glass fibres after saturation of epoxy. The fibre volume fraction was varied up to 50%. Tensile and wear tests were carried out to examine the improvement in the composite properties. A small deviation of the tensile strength and the elastic modulus from the calculated values using the rule of mixture was observed due to the existence of porosities. The wear resistance increases with increasing the sliding velocity, with decreasing the applied contact pressure and with selecting the most favourable glass fibre volume fraction.     

The mechanical behaviour of PEEK short fibre composites

Short glass (GF) and carbon fibre (CF) reinforced poly-ether-ether-ketone (PEEK) composites were prepared by injection moulding and then microstructurally characterized. Their mechanical behaviour was determined by two different methods: a classical unidirectional tensile test and an immersion ultrasonic technique. The reinforcing effect of fibres is discussed in the context of the theory of reinforcement of Bowyer and Bader. Interfacial shear strength and critical fibre length at break are calculated for both PEEK/GF and PEEK/CF composites. Examinations of fracture surfaces of uniaxial tensile specimens revealed a higher adhesion of carbon fibres to PEEK matrix in regards to the adhesion concerning glass fibre-PEEK interfaces, which is in agreement with the results provided by the model. Compatibility of ultrasonic and tensile results is reported.     

Microstructure and abrasive wear behaviour of iron base hardfacing

Abstract

The influence of the composition and heat treatment of overlays on the abrasive wear resistance of iron base hardfacing alloy overlays is reported. Overlays were deposited using a shielded metal arc (SMA) welding process on structural steel using two commercial hardfacing electrodes, i.e.Fe – 6%Cr – 0.7%C (H₁) and Fe – 32%Cr – 4.5%C (H₂). Abrasive wear resistance of overlays in as welded and heat treated conditions was tested using a pin on disc system against a 300 grade waterproof SiC polishing paper at different normal loads (1 – 4 N) and constant sliding speed 2.0 m s^-1. Optical microscopy was used to study the microstructure of overlays in as welded and heat treated conditions. SEM studies of wear surfaces were carried out to analyse wear mechanisms. It was found that the wear resistance of the high Cr – C coating is better than the low Cr – C hardfacing under identical conditions. Significant variation in hardness was noticed across the interface, indicating the effect of dilution. Hardness of the coating adjacent to the interface was found to be comparatively lower than the coating further away from the interface. Post-weld heat treatment enhanced the abrasive wear resistance.     

The tensile strength and ductility of continuous fibre composites

The plastic instability approach has been applied to the tensile behaviour of a continuous fibre composite. It is shown that the combination of two components with different strengths and degrees of work-hardening produces a new material with a new degree of work-hardening, which may be determined by the present analysis. Expressions for the elongation at rupture and the strength of a composite have been obtained and the results of the calculation are compared with some experimental data.List of symbols V _f volume fraction of fibres in composite - , , true strain of fibre, matrix and composite - s true stress - , , nominal stress on fibre, matrix and composite - _*, _*, _* critical stress of fibre, matrix and composite (ultimate tensile strength) - _*, _* critical strain of separate fibre and matrix - _* critical strain of composite - Q external load - A cross-sectional area - A ₀ initial value of area     

Review of current strategies to induce self-healing behaviour in fibre reinforced polymer based composites

Abstract

This paper addresses the various strategies to induce self-healing behaviour in fibre reinforced polymer based composites. A distinction is made between the extrinsic and intrinsic healing strategies. These strategies can be applied at the level of the fibre, the fibre/matrix interface or at the level of the matrix. It is shown that the degree of healing depends on the type of damage and the testing mode used and examples are given both for extrinsic and for intrinsic healing systems. The conclusion is drawn that self-healing in fibre reinforced composites is possible yet unlikely to become a commercial reality in the near future.     

Erosive wear behaviour of aluminium based composites

Al-MMCs reinforced with short fibres or particles of ceramics such as alumina, titanium diboride and silicon carbide result in composites of high specific strength and stiffness, suitable for advanced engineering applications such as in the aerospace and automotive industries. This paper studies the erosion wear behaviour of Al-based composites reinforced with alumina-fibre and in-situ TiB₂ particles using a water/SiC particles slurry jet. From the results of our experiment, the erosion resistance of reinforced Al-MMCs depends on that of the Al-alloy and the reinforcing ceramics, as well as on the bonding strength between the matrix and ceramic fibres or particles. Some design strategies to enhance the erosion resistance of Al-MMCs reinforced with short fibres and particles have been discussed.     

Non-linear elastic behaviour of flexible fibre composites

An elastic constitutive model is developed for flexible fibre composites which are composed of continuous curved fibres and ductile matrices. The prediction of non-linear stress/strain responses of the composites is performed by a stepwise incremental analysis. Numerical results of the uniaxial tensile stress/strain relations are obtained for several types of composites, containing glass or Kevlar fibres in an elastomeric polymer. Unique properties of the flexible composites are: (1) low Young's modulus in the range of low applied stress and high modulus in the range of high applied stress; (2) enhanced elongation; and (3) high energy associated with deformation.     

Anisotropic rheology of continuous fibre thermoplastic composites

The anisotropic rheology of continuous fibre thermoplastic composites has been resolved into along fibre and transverse components using a balanced pair of off-axis specimens in a commercial rotational rheometer with a parallel disc geometry. Existing theory has been used to demonstrate a small but consistent difference between the components of shear modulus and viscosity obtained from dynamic viscoelastic measurements. Transverse viscosity and yield stress are higher. The use of maximum shear rate (product of maximum shear strain and angular frequency), used here with apparent Maxwell viscosity, eliminates the strain dependence of the rates and correlates with steady shear viscosity and shear rate data. Differences in yield stress and viscosity are associated with the fibre-polymer system and the fibre volume fractions.