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The paper presents on the synergistic effect of two solid lubricants viz. thermo-graphite (TG) and hexa boron nitride (hBN – white graphite) in the composites when performance was evaluated in adhesive (against smooth mild steel disc) and in abrasive (against SiC paper) wear modes. The basic composition of matrix PEK (polyether ketone) (50%) and short glass fibers (30%) was kept constant and composites were designed with increasing amount of hBN (0, 5, 10, 15 and 20%) with simultaneous decrease of TG (20, 15, 10, 5 and 0). The composites were characterized for mechanical and tribological properties (in adhesive and abrasive wear modes). It was observed that the composites showed very good tribo-potential (very low wear rate and low friction) in adhesive wear mode. However, any of the SLs did not show great potential when included in isolation. Both showed synergism when existed in the composite in combination. The optimum amount was wear mode specific. For adhesive wear mode 15% TG and 5% hBN worked best while for abrasive wear mode 10% of each worked best. Overall TG proved better choice than hBN. Natural graphite proved superior to TG in adhesive wear mode, while trend was opposite for abrasive wear mode. The Lancaster–Ratner factor was observed to be responsible for controlling wear behavior. [ABSTRACT FROM AUTHOR]

Polymer and glass-fiber reinforced polymer composites are extensively employed in the aerospace and automotive industries. As a result, the demand for accurate machining of these materials has increased in recent years. Especially, the trend of miniaturization of the components or parts makes the micro-machining such as micro-milling very important in the machining area. In current study, an attempt has been made to better understand the micro-machinability of polyamide 6 and glass-fiber reinforced polyamide 6 manufactured by injection molding. To achieve this aim, tool wear, cutting force, surface roughness and burr formation during micro-milling of these materials were evaluated and results were compared. The experiments were conducted at various spindle speeds and feed rates and the influences of these parameters on output responses were investigated. It was concluded that forces increased with feed rate and spindle speed, but surface roughness decreased with spindle speed for both workpiece materials. Adhesion on micro tool was observed for unreinforced polyamide 6, however adhesion, abrasive wear, rounding of cutting edges and micro chipping were seen for glass-fiber reinforced polyamide 6. Protrusion of fibers, fiber failure/fracture and fiber/matrix debonding were observed on the workpiece surface when micro-milling was conducted at glass-fiber reinforced polyamide 6. It was found that the top burr size of down micro-milling was higher than that of up micro-milling for both materials. The main burr shape was wall type for unreinforced polyamide 6 and wavy burr for glass-fiber reinforced polyamide 6. From micro-machinability point of view, unreinforced polyamide 6 gave better results as compared to glass-fiber reinforced polyamide 6. [ABSTRACT FROM AUTHOR]

In this study, thermal aging process was applied to glass fiber (GF) and carbon fiber (CF) reinforced poly(ether ether ketone) PEEK composites and effects of this process and reinforcement type on thermal, thermomechanical, tribological, physical and morphological properties of PEEK composites were evaluated. All the results demonstrated that a transcrystalline layer was formed between the fiber and matrix in the composites under applied thermal aging condition and this layer affected the fiber–matrix adhesion, reduced the energy dissipation in this region and improved the properties of composites. As a result of this study, it was proved that the thermal aging process is an efficient method to control the thermal, thermomechanical, tribological and physical properties of composites and these properties of composites can be improved by using this method. [ABSTRACT FROM AUTHOR]

We experimentally investigated the effects of filler volume fraction of the phenol composites filled with porous particles on the fracture toughness and the wear rate against a smooth metal surface under multi-pass condition. Porous particles, made from rice husks, of various volume fractions from 0 to 0.5 were added to phenol resin as carbon filler. For the reported results of adhesive wear under multi-pass condition, we correlated the bulk parameters associated with the fracture toughness to the wear rate. We found an empirical power–law relation between the reciprocal of the product of stress and strain at rupture in bending test and the wear rate with various filler volume fractions. We also proposed the modified mixture law of the wear rate by taking account of the area fraction of transfer layer, which can provide a good prediction of the filler volume fraction dependence. [ABSTRACT FROM AUTHOR]

This experimental study is concerned with the influence of metallic (Ti) and ceramic (SiC) reinforcements in an aluminumfsilicon (AlSi) alloy, when regarding tensile properties and wear behavior. Several micron sized particulate reinforced composites were produced by hot-pressing technique: AlSi–SiC and AlSi–Ti composites and AlSi-(Ti–SiC) hybrid composites. Regarding tensile properties, all composites presented higher ultimate tensile strength (UTS) than the AlSi matrix, with the highest UTS being attained by a hybrid composite (AlSi-11.25%Ti–5%SiC). Regarding wear behavior, reciprocating pin-on-plate wear tests were performed for unreinforced AlSi; AlSi–Ti composites and AlSi-(Ti–SiC) hybrid composite against a gray cast iron (GCI) counterface. The wear mechanisms for all the tested tribopairs are presented and discussed. It was observed that the wear behavior of the AlSi–Ti/GCI and also AlSi-(Ti–SiC)/GCI tribopairs are improved when compared with the AlSi/GCI system. AlSi-11.25%Ti-5%SiC hybrid composite exhibited the highest improvement in wear rate. [ABSTRACT FROM AUTHOR]

A heterogeneous system with enhanced dielectric and tribological properties is developed for an electrostatic tuneable friction damper. Such system consists of a carbon fibre reinforced polymer stiffening element which is reversibly laminated onto a host structure by means of electrostatic fields. Damping is achieved when the maximum shear at the interface between stiffening element and structure exceeds the shear strength of the electrostatically laminated interface. The permittivity of the composite material, consisting of barium titanate particles in an epoxy matrix, follows the logarithmic mixing rule formulated by Lichtenecker. In order to exploit the beneficial effect of the high-permittivity filler material, a particle concentration of at least 30 % by volume is necessary. To improve the reduced wear resistance caused by the addition of such filler material, ceramic platelets are introduced and magnetically aligned. This measure reduces the wear volume by more than 70 % without affecting significantly its coefficient of friction. By increasing permittivity and the static friction coefficient, the required force to achieve damping can be realised at lower electric fields compared to commercially available polymer films. [ABSTRACT FROM AUTHOR]

Micro-structural characterization of the composites has revealed fairly uniform distribution and some amount of grain refinement in the specimens. Further, it was observed that the micro-hardness improve when increasing the milling time and the reinforcement content due to presence of hard Al 2 O 3 particles. Was also observed a low wear rate exhibited by the Al/Al 2 O 3 /Gr hybrid composites due to presence of Al 2 O 3 and Gr which they acted as load bearing elements and solid lubricant respectively. The observed wear rate and micro-hardness have been correlated with microstructural analyses. [ABSTRACT FROM AUTHOR]

This study is concerned with the influence of Nickel, as reinforcement, in an aluminum–silicon (AlSi) alloy when regarding wear behavior. For these composites, the effect of Ni content, in the tribopair performance, was evaluated. For this purpose, the pin but also the counterface wear behavior was analyzed. Nickel particulate reinforced aluminum–silicon (AlSi) composites, with 5, 12.5 and 20 wt.% Ni were produced by a hot-pressing route. Microstructural characterization showed a uniform distribution of the Ni particulates in the AlSi matrix. EDS and XRD analyses revealed that the particle/matrix interface was formed by Al 3 Ni intermetallic. Reciprocating pin-on-plate wear tests were performed with AlSi and AlSi–Ni pins against a gray cast iron (GCI) counterface. It was observed that the wear behavior of the AlSi–Ni/GCI tribopair is improved when compared with the AlSi/GCI system. [ABSTRACT FROM AUTHOR]

Abstract: Carbon fiber (CF) woven fabric (52% by weight) reinforced epoxy composite and carbon nanofiber (CNF, 12% by weight) paper coated on the surface of the CF/epoxy composite were fabricated by resin transfer molding (RTM). The surface erosion characteristics of molded CF composites were investigated by sand erosion test using silica particles with a size around 150μm as the erodent. The eroded surfaces were examined by scanning electron microscopy (SEM) and weight loss. The CNF paper was able to provide a much stronger erosion resistance compared to the CF reinforced epoxy composites, which is attributed to the high strength of CNFs and their nanoscale structure. Finite element (FE) computer simulations were used to qualitative interpret the underlying mechanisms. [Copyright &y& Elsevier]

Abstract: The aim of this study was to investigate the effects of matrix particle size, reinforcement particle size, volume fraction, and their interactions on the wear characteristics of Al–SiCp composites. Central composite design method was used to perform a series of experiments. The statistical analysis of experimental results showed that both main effect and interaction effect of factors investigated were effective on the wear behavior of Al–SiCp composites. Wear loss decreased as volume fraction increased; however, beyond volume fraction of 17.5%, it increased due to reinforcement particle clustering depending on volume fraction and matrix particle size to reinforcement particle size ratio. With decreasing of matrix particle size and increasing of reinforcement particle size, wear loss also decreased. However, after a certain volume fraction, large sized reinforcement particles had a negative effect on the wear resistance. [Copyright &y& Elsevier]

Abstract: The aim of this study was to investigate the erosive wear behavior of glass fiber, CaCO3 particle and glass fiber/CaCO3 hybrid reinforced ABS/PA6 blend based composites. The samples were prepared by using melt mixing and injection molding techniques. The mechanical, thermal, morphological properties and erosive wear behavior were investigated in terms of reinforcing agent type and composition. It was observed that the tensile strength and modulus values of hybrid composites gave a value between tensile strength and modulus values of only fiber reinforced composites and only particle reinforced composites. From DSC analysis it was revealed that Tg and Tm of composites were not significantly affected by reinforcement; however, degree of crystallinity was found to be sensitive to reinforcement type and composition. The impingement angle was found to have a significant effect on the erosive wear behavior. The results indicated that composite materials exhibited maximum erosion rate at impact angle of 30° conforming their ductile erosion behavior. In order to investigate wear mechanisms, eroded surface analysis was done by scanning electron microscopy. Surface analysis showed that repeated impact of hard silica sand particles caused a local removal of the matrix from the fiber surface and led to form craters on the surface of the composite material. [Copyright &y& Elsevier]

Abstract: Metal matrix composite (MMC) focuses primarily on improved specific strength, high temperature and wear resistance application. Aluminium matrix reinforced with titanium carbide (Al–TiCp) has good potential. The main challenge is to produce this composite in a cost effective way to meet the above requirements. In this study Al–TiCp castings with different volume fraction of TiC were produced in an argon atmosphere by an enhanced stir casting method. Specific strength of the composite has increased with higher % of TiC addition. Dry sliding wear behaviour of AMC was analysed with the help of a pin on disc wear and friction monitor. The present analyses reveal the improved specific strength as well as wear resistance. [Copyright &y& Elsevier]

Abstract: We investigated the effect of carbon nanotube (CNT) modifications on the flexural and wear behaviors of multiscale carbon/CNT/epoxy composites in this study. Carbon/epoxy woven composites and two types of multiscale carbon/CNT/epoxy composites were fabricated by incorporating woven-type carbon fibers into epoxy matrices modified with 2wt% acid-treated and silane-treated multi-walled carbon nanotubes (MWCNTs). Three-point bending and ball-on-disk wear tests were performed on the three composites. The results showed that the flexural moduli and strengths of carbon/CNT/epoxy composites were greater than those of carbon/epoxy composites, regardless of CNT modification. Specifically, the flexural modulus and strength of the silane-treated specimens were 10% and 15% greater, respectively, than those of the acid-treated samples. The results also showed that the wear properties of carbon/epoxy composites are improved by the addition of CNTs. In addition, the wear properties of silane-treated samples were superior to those of acid-treated samples. Scanning electron microscopic examination of fractured and worn surfaces showed that the improvement in the flexural and wear properties of the silane-treated carbon/CNT/epoxy composites was attributed to the improved dispersion of CNTs in the epoxy and the better interfacial characteristics caused by the silanization of the CNTs. [Copyright &y& Elsevier]

Abstract: In this work, nano-SiO2 particles filled polyetheretherketone (PEEK), with nano-SiO2 contents ranging from 0.5 to 4vol.%, were compounded by a ball milling process performed under room temperature. Nanocomposites were prepared through compression molding as-milled PEEK/nano-SiO2 mixtures without further melt mixing. Differential Scanning Calorimetry (DSC) thermograms indicate that the ball milling process can impose a non-equilibrium order in PEEK due to its repetitive deformation. The incorporation of nano-SiO2 leads to a significant improvement in material stiffness and a decrease in material ductility. Fractography analyses suggest that secondary cracks initiating from the nanoparticles as a result of stress concentration are responsible for the parabolic markings and dimples observed in the fracture initiation regions of the nanocomposites with different nano-filler contents. The wear resistance of PEEK is significantly improved after incorporating nano-SiO2 and at a rather low nano-SiO2 loading, i.e. 1vol.%, the composite presents the optimum wear resistance. [Copyright &y& Elsevier]

In the present study, the effects of different matrix compositions, namely, Al, Al–3.35 wt.% Cu and Al–4.08 wt.% Mg, on the resulting gradient of the SiC particulates along the bulk functionally graded materials (FGMs) synthesized by the simple, cost-effective, high yield and high deposition rate gradient slurry disintegration and deposition technique is investigated. For Al/SiCp and Al–Cu/SiCp, an increase in weight percentage of SiCp along the deposition direction with an attendant increase in porosity and microhardness was observed. However, for Al–Mg/SiCp, reverse SiCp gradient was observed, with porosity and microhardness decreasing along the deposition direction. A lower overall porosity was also observed for Al–Mg/SiCp. A reduction in CTE value of the high SiCp end was observed when compared with the low SiCp end for all three ingots. The high SiCp end was also found to be more wear resistant than the low SiCp end, except for Al–Cu/SiCp. The effects of different Al matrix compositions with the microstructural development, microhardness and wear results are correlated. [Copyright &y& Elsevier]

The objective of this work is to develop aramid pulp/carbon fiber-reinforced polybenzoxazine composites as high performance friction materials. Effects of aramid pulps and carbon fibers on thermal stability, mechanical properties, and tribological performances of the composites are investigated. Aramid pulps could enhance friction coefficient and friction stability of the composites, while thermal stability, mechanical properties, and wear resistance of the composites are improved with an addition of carbon fibers. The composites exhibit high thermal degradation and glass transition temperatures, high and stable friction coefficient, and good wear resistance. The developed polybenzoxazine composites could be applied as non-asbestos organic friction materials. Image 1 • High performance friction materials based on polybenzoxazine composites are developed. • Combined reinforcing fibers including aramid pulp and carbon fibers are employed. • High thermal stability and rigidity of the polybenzoxazine binder enhance friction behavior of polybenzoxazine composites. • Polybenzoxazine composites exhibited good tribological performances at elevated temperatures, i.e. 350 °C. [ABSTRACT FROM AUTHOR]