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Flexible piezoelectric pressure sensors have been paid great attention in wearable electronic devices, obtaining mechanical energy and driving portable devices. Presently, membranes based on piezoelectric ceramic/polymer composite materials encounter problems such as filler agglomeration and surface defects, which affects the energy conversion performance of piezoelectric devices. Herein, the surface of lead zirconate titanate (Pb(Zr0.52Ti0.48)O3, PZT),was modified by coupling agent-polydopamine (Pdop), and combined with the polyimide (PI) matrix by in-situ polymerization to form a uniform Pdop@PZT/PI composite. This polydopamine modification method increases the compatibility between the two components, and promotes the dispersion of PZT in the polyimide matrix more uniform. Under the external force of 10 N, the maximum open circuit voltage of Pdop@PZT/PI-based piezoelectric pressure sensor (PPS) can reach 12.8 V. In addition, the sensitivity of the sensor is 1.4 V/N (0.24 V/kPa), which can maintain a stable output voltage under different frequencies of external force. After 10,000 cycles of periodic impacting/releasing, the open circuit voltage of PPS remained stable, indicating that the device has excellent stability and durability. It has the potential to be used as self-powered wearable sensors and detect human motion in daily life.

High temperature self-lubricating NiAl matrix composites with addition of CuO (15, 20, and 25wt.%) were fabricated by powder metallurgy technique, and the tribological behavior from room temperature to 1000°C was investigated. It was found that Ni-Cu and Al20 3 phases formed during the fabrication process due to reaction of NiAl and CuO. The tribological results showed that the composite with addition of 25wt.% CuO has a favorable friction coefficient of about 0.2 and excellent wear resistance with the magnitude of 10-6 mm³ N-1 m-1 at high temperatures (800 and 1000°C). [ABSTRACT FROM AUTHOR]

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]

Unidirectional carbon fiber reinforced epoxy was tested in ambient air at three different levels of relative humidity and under full immersion in demineralized water. Reciprocating sliding tests were performed at 23 °C against either stainless steel or alumina balls moving in parallel or anti-parallel direction to the fibers. We demonstrate in this work that humidity and water immersion affect significantly the fiber debonding. Under sliding against stainless steel or alumina at low relative humidity, fiber debonding is more pronounced than at high relative humidity and at water immersion. The wear depth increases with increasing relative humidity when sliding against stainless steel, whereas it remains practically constant against alumina. For all test conditions, the wear depth is larger when tested against stainless steel than against alumina. It was found that the thin moisture film formed at the surface of the stainless steel counter body leads to a higher corrosive risk than water immersion. More precisely, we demonstrate that high humidity leads to the production of oxide debris originated from the stainless steel ball which increases markedly the wear by abrasion. These debris lead to a high fluctuation of the coefficient of friction measured on carbon fiber reinforced epoxy composite sliding against stainless steel at 85% RH, whereas a steady state coefficient of friction is noticed against alumina. [ABSTRACT FROM AUTHOR]

The main focus of this work is to built an experimental database which may be helpful to the research and development on the design and qualification of composite repairs for aircraft structures. Glass-epoxy (G-E), carbon-epoxy (C-E) and hybrid laminated bidirectional composites were manufactured, characterized and then compared. The influence of hygrothermal conditions on p erformance of such fiber-reinforced polymer (FRP) composites was also investigated. Several durations of conditioning at 24 ± 3, 70 and 90 °C in distilled water were retained. Both time and aging temperature were combined in order to better highlight the impact of aging on the performance of the studied composites. When exposed to water, all composites displayed a Fickian sorption behavior. Due to its hydrophilicity and its polarity, G-E composites showed the greater diffusion coefficient and the maximum moisture content. Whereas, the C-E composites exhibited the best mechanical behavior when they are subjected to tensile, flexure and wear. On the other hand, over prolonged periods of immersion, water induced a noticeable degradation and resulting structural changes were recorded indicating that the durability of these composites was affected. In particular, G-E composites showed higher sensitivity to aging in comparison with C-E and hybrid composites. In all cases, the reduction in mechanical properties is caused by matrix plasticization due to moisture and temperature. Finally, the study of time temperature superposition (TTS) allows establishing a correlation between exposure to moisture and temperature and the mechanical behavior for the studied laminated. [ABSTRACT FROM AUTHOR]

A metallic matrix composite, with AlSi9Cu3 matrix reinforced with 5% copper coated graphite (Gr Cu ) was processed in semi solid state by centrifugal casting. This technique allows the uniform controlled distribution of the reinforcing material to provide improved tribological properties in certain area. The graphite particles were copper coated for a better embedding in the matrix. The microstructure evolution revealed compounds containing Mn, Si and Mg in the matrix alloy and the final composite and controlled distribution of the copper coated graphite as reinforcing material. The hardness measurement showed 48% improvement towards the matrix alloy and the Young modulus showed 27% improvement. The friction coefficient and wear rate obtained revealed a very good and promising behavior of the composite processed in semi solid state for ball bearings ring application. [ABSTRACT FROM AUTHOR]

The aim of the present work is to investigate the influence of the reinforcing material and architecture on the voids content, mechanical properties and tribological behavior of fiber reinforced epoxy composite laminates manufactured by VARTM under different processing conditions. Two different textile architectures, namely unidirectional non-crimp fabrics (UD) and 0/90 plain wave (PW), were considered, reinforcing an EPIKOTE RIMR 135 epoxy matrix with glass (GF) as well as carbon (CF) continuous fibers. Optical observations revealed an unexpected trend relatively to the intra- and inter-bundle voids concentration with respect to the impregnation velocity, especially using UD-CF and UD-GF reinforcements and low impregnation rate. Tensile and three points bending tests highlighted the dominant role of fiber material and architecture on mechanical properties, whereas the presence of voids played a minor role with respect to the analyzed features. Tribological outcomes evidenced a reduction of the friction coefficient (μ) when the resin is reinforced by carbon or glass fibers. The lowest values were detected when the sliding direction of the counterbody is oriented parallel to the fiber direction for UD samples. Further reduction of μ, for both UD and PW specimens, was obtained by interposing a lubricant at the interface. [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]

The effects of atomic oxygen exposure on pure polyimide and nano-ZrO 2 reinforced polyimide composites were investigated in a ground-based simulation facility. The experimental results indicated that the surface structure of both pure polyimide and ZrO 2 /polyimide composites were destroyed by atomic oxygen attack, but the addition of nano-ZrO 2 particles in polyimide could obviously decrease the mass loss, which showed that ZrO 2 could enhance the atomic oxygen resistance. The results of ZrO 2 /polyimide composites before and after atomic oxygen exposure showed that atomic oxygen irradiation aggravated the friction and wear of the ZrO 2 /polyimide composites. The wear mechanism was mainly abrasive particles wear arising from the ZrO 2 -rich layer on the surface of composites. The ZrO 2 /polyimide composites with 1 wt% nano-ZrO 2 owns the lowest varying rate of the friction coefficient and wear rate before and after atomic oxygen exposure, which showed stable friction and wear properties and was expected to become a kind of potential tribological materials for practical spacecraft designation. [ABSTRACT FROM AUTHOR]

Rapid innovation in nanotechnology in recent years enabled development of advanced metal matrix nanocomposites for structural engineering and functional devices. Carbonous materials, such as graphite, carbon nanotubes (CNT's), and graphene possess unique electrical, mechanical, and thermal properties. Owe to their lubricious nature, these carbonous materials have attracted researchers to synthesize lightweight self-lubricating metal matrix nanocomposites with superior mechanical and tribological properties for several applications in automotive and aerospace industries. This review focuses on the recent development in mechanical and tribological behavior of self-lubricating metallic nanocomposites reinforced by carbonous nanomaterials such as CNT and graphene. The review includes development of self-lubricating nanocomposites, related issues in their processing, their characterization, and investigation of their tribological behavior. The results reveal that adding CNT and graphene to metals decreases both coefficient of friction and wear rate as well as increases the tensile strength. The mechanisms involved for the improved mechanical and tribological behavior is discussed. [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]

Multilayer graphene (MLG) shows an attractive prospect for the demanding engineering applications. This paper reports the mechanical and tribological properties of MLG reinforced Ni 3 Al matrix composites (NMCs) under dry sliding at varying sliding speed. The hardness and elastic modulus of the NMCs are significantly influenced with MLG content. It is found that the hardness and elastic modulus of the NMCs are found to be increased by increasing MLG content up to 1.0 wt.%, while decreased when MLG content is above 1.0 wt.%. Tribological experiments suggest that MLG can dramatically improve the wear resistance and decrease the friction coefficient of the NMCs. Such marked improvement of wear resistance is attributed to the reinforcing mechanisms of MLG, such as crack deflection and pull-out, and reduction of friction coefficient is related to the formation of a tribofilm on the sliding contact surface. [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]

In order to clarify the effects of carbon fiber size on the properties of carbon fiber/high strength glass fabric (HSGF)/phenolic laminate, two kinds of laminates modified by nano-sized carbon fibers (CNFs) and micro-sized carbon fibers (CMFs), were respectively fabricated. The interlaminar shear strength (ILSS) and tribological properties of HSGF/phenolic laminates modified by CNFs and CMFs in water environment were comparatively investigated. Results showed that CNFs at proper contents ranging from 1.0% to 3.0% can enhance ILSS of HSGF/phenolic laminate, while CMFs deteriorated the ILSS. After water immersion, ILSS of the laminates modified by CNFs at 1.0–3.0% were just slightly decreased; however, those of the laminates modified by CMFs suffered larger drop. On the other hand, however, CMFs were more effective than CNFs in improving the wear resistance of HSGF/phenolic laminate in water. [ABSTRACT FROM AUTHOR]

Abstract: High pressure gasoline direct injection systems are able to considerably reduce both the fuel consumption and the harmful emissions, but the current metallic components should be replaced by new advanced materials with enhanced tribological properties. In this work, multi-walled carbon nanotubes (MWCNTs)/silicon nitride (Si3N4) nanocomposites have been tested in a high-pressure 3-piston prototype pump for gasoline using both a cam/pusher self-mated system, and a nanocomposite cam/steel AISI 52100 pusher configuration. Si3N4 sliding systems were also tested as reference material. MWCNTs nanocomposite cams in combination with steel pushers present an outstanding performance at high rotation speeds and delivery pressures, showing mechanical efficiencies beyond 0.95, low cyclic variations, and torque oscillations 75% lower than the other tested material combinations. MWCNTs favour the formation of surface dimples where debris are entrapped, and promote tribochemical reactions with the steel pushers, enhancing the mechanical efficiency. [Copyright &y& Elsevier]

Abstract: This paper develops an elliptic vibration-assisted (EVA) technique to effectively cut fibre-reinforced polymer (FRP) composites using a simple tool. A novel vibrator was invented to work at the anti-resonant frequency to realize stable and high variational velocities. A three-dimensional microstructure-based finite element model was also established to explore the material removal mechanisms in the EVA cutting. It was found that the application of vibration can significantly decrease the cutting forces and reduce the subsurface damage in a workpiece. The vibration in the cutting direction is more effective in reducing the cutting force, but that normal to the cutting direction has the advantage of chip removal. When the vibration is applied to both the directions in the EVA cutting, an optimal cutting process can be reached, providing much smaller cutting forces, a much improved surface integrity, and an extended tool life. The study concluded that the ratio of the tool-feed-rate to the maximum vibration velocity in the cutting direction, and the ratio of the cutting distance in a single tool vibration cycle to the fibre diameter are the key parameters. To maximise the advantage of the EVA cutting, it is necessary that these two parameters are below their critical values. [Copyright &y& Elsevier]

Abstract: Si3N4–Ni60 is firstly used to improve the wear resistance of a TA7 (Ti–5Al–2.5Sn) titanium alloy surface by mean of a laser alloying (LA) technique. The synthesis of the hard composite coating on a TA7 titanium alloy by LA of Ni60–Si3N4 pre-placed powders was investigated by means of scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and high resolution transmission electron microscope (HRTEM). Experimental results indicated that a number of the interdendritic lamellar eutectics, nanoscale ceramics (NC) and the amorphous phases were produced in such LA coating. The production of NC led the free energy to enhance, which increased the density of point defect, leading to the formation of hypersaturated state of point defect, causing lattice distortions. Compared with a TA7 alloy substrate, an improvement of the wear resistance was obtained for such LA composite coating. [Copyright &y& Elsevier]

Abstract: An investigation is conducted on the effect of the hybrid of multi-wall carbon nanotubes (MWCNTs) and graphene oxide (GO) nanosheets on the tribological performance of epoxy composites at low GO weight fractions of 0.05–0.5phr. The MWCNT amount is kept constant at 0.5phr, which is typical for CNT/epoxy composites with enhanced mechanical properties. Friction and wear tests against smooth steel show that the introduction of 0.5phr MWCNTs into the epoxy matrix increases the friction coefficient and decreases the specific wear rate. When testing the tribological performance of MWCNT/GO hybrids, it is shown that at a high GO amount of 0.5phr, the friction coefficient is decreased below that of the neat matrix whereas the wear rate is increased above that of the neat matrix. At an optimal hybrid formulation, i.e., 0.5phr MWCNTs and 0.1phr GO, a further increase in the friction coefficient and a further reduction in the specific wear rate are observed. The specific wear rate is reduced by about 40% down to a factor of 11 relative to the neat epoxy when the GO content is 0.1phr. [Copyright &y& Elsevier]

Abstract: The advantage of concrete containing nano-TiO2 in resisting the coupled effects of chloride diffusion and scouring with respect to pure concrete was studied in this paper. Because of the movement in exposed concrete surface induced by scouring and the deterioration in concrete microstructure caused by chloride salt accumulation, an increasing mutual accelerative effect between the chloride diffusion and the scouring abrasion was experimental observed, which agreed with the theoretical simulation results. Benefited from the improvement in microstructure and porosity compared with the pure concrete, concrete containing 1% nano-TiO2 in the weight of cement showed a better impermeability as well as the abradability. Correspondingly, a better performance in resisting the coupled effects of chloride diffusion and scouring was founded for the concrete containing nano-TiO2 compared to the pure concrete, and this advantage increased upon the time. [Copyright &y& Elsevier]

Abstract: This work investigated the influence of graphite on the wear behavior of Al 7075/Al2O3/5wt.% graphite hybrid composite. The investigation reveals the effectiveness of incorporation of graphite in the composite for gaining wear reduction. The Al 7075 (aluminium alloy 7075) reinforced with Al2O3–graphite were investigated. The composites were fabricated using liquid metallurgy route. Ceramic particles along with solid lubricating materials were incorporated into aluminium alloy matrix to accomplish reduction in both wear resistance and coefficient of friction. The Al 7075/Al2O3/graphite hybrid composite was prepared with 5wt.% graphite particles addition and 2, 4, 6 and 8wt.% of Al2O3. The hardness, tensile strength, flexural strength and compression strength of the Al 7075–Al2O3–graphite hybrid composites are found to be increased by increased weight percentage of ceramic phase. The wear properties of the hybrid composites containing graphite exhibited the superior wear-resistance properties. [Copyright &y& Elsevier]

Abstract: This work investigates 7075 aluminium alloy–graphite composites for its tribological and mechanical behaviour under dry sliding conditions. The conventional liquid casting technique was used for the fabrication of composite material and subjected to T6 heat treatment. The reinforcement content was chosen as 5, 10, 15 and 20wt.% of graphite to identify its potential for self-lubricating property under dry sliding conditions. Wear tests were conducted by using pin on disc apparatus to evaluate the tribological behaviour of the composite and to determine the optimum content of graphite for its minimum wear rate. The wear rate decreases with addition of graphite content and reaches its minimum at 5wt.% graphite. The wear mass loss was found to decrease with increasing sliding distance. The average coefficient of friction decreases with addition of graphite content and was found to be minimum at 5wt.% graphite. The mechanical properties of the composites and base alloy were tested. The mechanical properties decrease with increasing graphite content as compared to base alloy. The worn surfaces were examined through SEM. The presence of 5wt.% graphite in the composites can exhibit superior wear property as compared to base alloy. [Copyright &y& Elsevier]

Abstract: Semimetallic friction composites (SMFCs) consisting of epoxidized natural rubber (50mol% epoxidation, ENR 50), alumina nanoparticles, steel wool, graphite, and benzoxazine were prepared via melt mixing using a Haake internal mixer at 90°C and 60rpm rotor speed. The composites were vulcanized using sulfur and electron-beam (EB) crosslinking systems. The SMFC samples were then subjected to friction, hardness, porosity, and density tests to determine their friction and wear properties. The morphological changes in the samples were also observed under a scanning electron microscope. The friction and wear properties of SMFCs crosslinked via the EB irradiation and sulfur vulcanization systems were compared. The friction coefficients in normal and hot conditions, as well as the hardness and density of the irradiated SMFC, were higher than those of the sulfur-vulcanized samples at all applied doses. The porosity of the irradiated SMFC at 50, 100, and 150kGy was higher than that of the sulfur-vulcanized samples; however, the irradiated SMFC exhibited a descending trend at 200kGy. On the other hand, the specific wear rates of the irradiated samples were lower than those of the sulfur-vulcanized samples at all applied doses. The sample crosslinked via EB irradiation at 150kGy exhibited the greater tribological property compared with the sulfur-vulcanized SMFC, as indicated by the higher friction coefficient (approximately 0.461) and lower wear rate achieved at 150kGy irradiation. [Copyright &y& Elsevier]

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: In the present investigation, the influence of B4C on the mechanical and Tribological behavior of Al 7075 composites is identified. Al 7075 particle reinforced composites were produced through casting, K2TiF6 added as the flux, to overcome the wetting problem between B4C and liquid aluminium metal. The aluminium B4C composites thus produced were subsequently subjected to T6 heat treatment. The samples of Al 7075 composites were tested for hardness, tensile, compression, flexural strengths and wear behavior. The test results showed increasing hardness of composites compared with the base alloy because of the presence of the increased ceramic phase. The wear resistance of the composites increased with increasing content of B4C particles, and the wear rate was significantly less for the composite material compared to the matrix alloy. A mechanically mixed layer containing oxygen and iron was observed on the surface, and this acted as an effective insulation layer preventing metal to metal contact. The coefficient of friction decreased with increased B4C content and reached its minimum at 10vol% B4C. [Copyright &y& Elsevier]

Abstract: In the present study, effect of Zr addition on the microstructure and wear behavior of aluminum alloy composites (AMCs) reinforced with B4Cp and SiCp particles fabricated via hot pressing were investigated. The samples for the study composed of unreinforced aluminum alloy (Alumix 123) and the composites reinforced with 10% B4Cp and % SiCp were prepared by hot isostatic pressing (HIP) method. Similarly, all the samples alloyed with 0.2% Zr were also produced in order to make a comparison. The produced samples were evaluated for microstructural properties and mechanical tests for hardness, tensile and bending strength were performed. Wear test was carried out at 5mm/s sliding speed under 3.0N load for the all kind of hot pressed produced samples. The hot pressed composite microstructures have a more uniform distribution of the reinforcements. After HIP process, the composites were successfully produced with high density (>99%). The addition of Zr increased the yield and tensile strength of the samples. The highest strength value was found for the sample Al 123 matrix alloy with Zr. Evaluation of microstructures showed that copper and zirconium dispersed equally within the matrix microstructure without agglomeration. For the composite samples, Al3Zr, appeared as white precipitate, were inspected around B4C and SiC particles. The composite containing SiC particles and Zr had wear resistance value superior to those of the other counterparts. [Copyright &y& Elsevier]

Abstract: NiCr/Cr3C2–WS2–CaF2 mixed powders were designed and aimed to fabricate high temperature self-lubricating wear-resistant composite coating by laser cladding. The friction and wear properties of the coating were investigated under different temperatures and loads against Si3N4 ceramic ball. Results show that friction coefficient decreases with the increasing temperature while the wear rate firstly decreases and then increases with the increasing temperature. Both the friction coefficient and wear rate firstly decreases and then slightly increases with the increasing normal load. The coating exhibits relatively excellent tribological behavior under moderate temperature and moderate normal load. [Copyright &y& Elsevier]

Abstract: This paper presents the wear behaviour of Al6061-T6 discontinuously reinforced with silicon carbide (SiC) and aluminium oxide (Al2O3) composite. The test specimens are prepared and tested as per ASTM standard. The experiments are conducted by using a pin on disc wear tester. Empirical relation is established to estimate the wear using statistical regression analysis and analysis of variance (ANOVA). The results indicated that the wear resistance of the 15% hybrid composite is better than that of the 5% composite. The fracture surface of composites shows the ductile tear ridges and cracked SiC and Al2O3 particles indicating both ductile and brittle fracture mechanism. [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: We proposed a new method for quantifying the micro/nano-scale wear volume (i.e., volume of wear loss) to characterize the wear-resistance of nanocomposites. Effects of wear load, pass (a pattern of scan cycles), and nanoparticle content on the wear behavior of silica nanoparticle-reinforced composites (EP/SiO2) were studied. The multiple nano-scratch patterning technique was carried out for the wear test. Images of sample surface, before/after the test, obtained using in situ scanning probe microscopy (SPM) were used to calculate the wear volume. Our results indicate that the wear mechanism transits from a plastic-deformation dominated mode to a fatigue-wear dominated mode with increased wear load and pass. The threshold at which transition occurs increases with the nanoparticle content, and correlates with improvement in wear resistance of nanocomposites. This transition threshold can be a different metric, rather than using the conventional mechanical properties (e.g., surface hardness and stiffness), to characterize the wear resistance of materials such that wear load and pass is taken into account. [Copyright &y& Elsevier]

Abstract: High-performance self-lubricated ceramic composites are regarded as potential candidates for space applications. This paper proposes a new design for alumina ceramic self-lubricating composites in order to overcome the conflict between their mechanical and tribological properties. Complying with the design principle of bionic and graded composites, Al2O3/Al2O3–ZrO2(3Y)/SL composites with laminated-gradient structure were prepared, and their mechanical and tribological properties were studied. The results show that this newly-developed ceramic composite achieves satisfactory strength and tribology properties compared with the traditional ceramic self-lubricated composites. The bending strength, which was five times higher than that of traditional Al2O3 self-lubricated composites, reached the same level as the properties of general monolithic Al2O3 ceramics. In the temperature range of 25–800°C, the friction coefficient of Al2O3/Al2O3–ZrO2(3Y)/SL composite was less than 0.54, which was about half of that of monolithic Al2O3 ceramics. [Copyright &y& Elsevier]

Abstract: Composites of calcium hydroxyapatite (HA) powders containing 0–50vol.% of ZrO2 nanopowder with 3mol% Y2O3 (3YSZ) were consolidated very rapidly under pressure by high-frequency induction heating sintering (HFIHS). The effects of the addition of 3YSZ on the relative density, hardness, fracture toughness, wear resistance and grain growth were studied. All of the sintered samples were analyzed by X-ray diffraction (XRD) to determine the phase content. The calcium HA with 20vol.% 3YSZ showed optimal combination of properties in terms of relative density, hardness and fracture toughness, which caused superior sliding wear performance under the test conditions examined. The degradation of the properties of HA with 40 and 50vol.% 3YSZ was attributed to a combination of some decomposition of HA into tricalcium phosphate (TCP) and some residual porosity. On the contrary, the HA composite with 10vol.% 3YSZ content appeared to be weakened little by YSZ as a strengthening agent. The results revealed the effectiveness of the HFIHS method for achieving near theoretical densities without significant grain growth for the geometry of the sample studied. [Copyright &y& Elsevier]

Abstract: The influences of various process parameters on the particle segregation ratio and the particle distributions involving the particle size and volume fraction of in situ primary Si/Mg2Si particles in tubes of Al–Si–Mg functionally graded materials (FGMs) fabricated by centrifugal casting were systematically investigated. The properties of hardness, wear resistance and thermal expansion of the tubes were examined. The results show that, (1) the FGMs tubes consisted of a reinforcement layer and an un-reinforcement layer; (2) the particle segregation ratio varied with various process parameters; (3) the volume fractions and sizes of primary Si/Mg2Si particles presented a graded distribution in the reinforcement layer; and (4) the FGMs had an advantage over the conventional motorcycle/automobile cylinder liners and the conventional materials Al–12Si–1Cu–1Mg–1Ni alloy in the wear resistance and the thermal expansion property, respectively. [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: An extensive tribological and mechanical study was performed on the epoxy-based nanocomposites reinforced with low contents of nanodiamond (ND) particles. Consistent rising in the hardness values and considerable decrease in the wear rate and coefficient of friction values were observed. It was found that the addition of only 0.1wt.% of ND decreases the coefficient of friction and the wear rate 50% and 84%, respectively. Furthermore, despite improvement in the mechanical properties of epoxy/0.1wt.% ND, the addition of higher amounts of nanofillers hindered more enhancements. The mechanisms involved in the tribological and the mechanical behaviors have also been discussed in detail. [Copyright &y& Elsevier]

Abstract: In flooring applications, experimental data and insight from scientific investigations on wear properties of wood/polymer composites (WPCs) are important for engineers to understand how to design and formulate WPC materials with high resistance to wear. In this work, three different types of wood flour – namely Xylia kerrii Craib & Hutch., Hevea brasiliensis Linn., and Mangifera indica Linn. – were utilized and incorporated into poly(vinyl chloride) (PVC) with a fixed content (10phr) of E-chopped strand glass fiber. The physical, mechanical and wear properties, in terms of specific wear rate, were then assessed as a function of wood content and sliding distance. The experimental results suggested that the addition of wood flour increased the flexural modulus and strength up to 40phr; beyond this concentration, the flexural properties decreased. Hardness was not affected by the addition of wood flour. The mechanical and wear properties of WPVC composites were found to improve with the addition of the E-glass fiber. Xylia kerrii Craib & Hutch. wood exhibited the lowest specific wear rate for non-reinforced WPVC composites, whereas Hevea brasiliensis Linn. wood showed the lowest specific wear rate for the glass fiber reinforced WPVC composites. The longer the sliding distance, the greater the specific wear rate in all cases. [Copyright &y& Elsevier]

Abstract: The influences of normal contact pressure and sliding velocity on self-lubricating property of PTFE-based composite filled with nano-serpentine particles were mainly studied in the range of 0.12–0.96m/s and 1.43–8.55MPa. For comparison, the friction and wear experiments of pure PTFE also were carried out under the same conditions. A scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) were employed to examine the worn surfaces of PTFE/serpentine nanocomposite and transfer films. The experimental results showed that normal contact pressure and sliding velocity had significant effects on the tribological performances of PTFE/serpentine composite. Under different loads, the nanocomposite suffered from abrasive wear, fatigue wear and adhesive wear successively. And at different sliding velocity, the main wear mechanisms were abrasive wear and adhesive wear. SEM and EDS analyses indicated that the continuous and uniform transfer film generated on counterfaces acted as a solid lubricant, which was important to improve the self-lubricating property of PTFE/serpentine nanocomposite. [Copyright &y& Elsevier]

Abstract: In this study, the effect of surface modification of aluminum powders on the tensile, fracture, and tribological behaviors of aluminum/epoxy composites was investigated. Aluminum powders were surface-modified with 3-aminopropyltriethoxysilane. Aluminium/epoxy composites were fabricated by cast molding method using 10wt.% untreated and silane-treated aluminium powders. Tensile, mode I fracture, and tribological tests were performed on both composites. The results showed that the tensile modulus and strength of silane-treated aluminum/epoxy composites were ∼9% and ∼12% greater, respectively than those of untreated aluminum/epoxy composites. The results also showed that the fracture toughness and wear resistance of silane-treated aluminum/epoxy composites were ∼32% and ∼56% greater than that of untreated aluminum/epoxy composites. Scanning electron microscope (SEM) examination showed the improvement of tensile and fracture properties of silane-treated aluminum/epoxy composites was attributed to the improved dispersion and bonding of aluminum particles in the epoxy, due to the silanization of aluminium powders. [Copyright &y& Elsevier]

Abstract: Drilling and fastening of hybrid materials in one-shot operation reduces cycle time of assembly of aerospace structures. One of the most common problems encountered in automatic drilling and riveting of multimaterial is that the continuous chips curl up on the body of the tool. Drilling of carbon fiber reinforced plastic (CFRP) is manageable, but when the minute drill hits the aluminium (Al) or titanium (Ti), the hot and continuous chips produced during machining considerably damage the CFRP hole. This study aims to solve this problem by employing nano-coated drills on multimaterial made of CFRP and aluminium alloy. The influence of cutting parameters on the quality of the holes, chip formation and tool wear were also analyzed. Two types of tungsten carbide drills were used for the present study, one with nano-coating and the other, without nano coating. The experimental results indicated that the shape and the size of the chips are strongly influenced by feed rate. The thrust force generated during drilling of the composite plate with coated drills was 10–15% lesser when compared to that generated during drilling with uncoated drills; similarly, the thrust force in the aluminium alloy was 50% lesser with coated drills when compared to thrust force generated without coated drills. Thus, the use of nano-coated drills significantly reduced the surface roughness and thrust force when compared with uncoated tools. [Copyright &y& Elsevier]

Abstract: Particulate reinforced Al-MMCs exhibits better mechanical properties and improved wear resistance over other conventional alloys. In the present paper, the experimental results of the mechanical and tribological properties of Al6061–SiC composites are presented. The composites of Al6061 containing 2–6wt% SiC were prepared using liquid metallurgy route. The experimental results showed that the density of the composites increase with increased SiC content and agrees with the values obtained through the rule of mixtures. The hardness and ultimate tensile strength of Al6061–SiC composites were found to increase with increased SiC content in the matrix at the cost of reduced ductility. The wear properties of the composites containing SiC were superior to that of the matrix material. [Copyright &y& Elsevier]

Abstract: In the present study, sliding wear tests were carried out on different sizes and volume fractions of coated B4C particles reinforced 2024 aluminum alloy composites fabricated by a squeeze casting method. Microstructural examination showed that the B4C distributions were generally homogeneous in the matrix while some particle clusterings were observed at relatively high particle containing composites. As compared to the 2024 Al matrix alloy, the hardness of the composites was found to be greater. It is observed that the wear resistance of the composites was significantly higher than that of the unreinforced aluminum alloy, and increased with increasing B4C particles content and size. The hard B4C particles act as a protrusion over the matrix, carries a major portion of the applied load and protect the abrasives from penetration into the specimen surface. Combination of rough and smooth regions is distinguished on the worn surface of the composites. The depth and number of grooves in composites decreased with increasing volume fraction of B4C particles, and the worn surfaces of composites were relatively smooth. [Copyright &y& Elsevier]

Abstract: Ti3Al–matrix composites were prepared by laser cladding of the Al3Ti/TiB2/Al2O3 pre-placed powders on the Ti–6Al–4V alloy, which can improve the wear resistance of the substrate. With addition of the proper content of RE oxides (nano-Y2O3), this composite coating exhibited finer microstructure and better wear resistance. Nevertheless, excessive RE oxides could lead to the production of the micro-crack, and also decrease the temperature of the molten pool leading to the present of the un-melted TiB2 block, which can significantly decrease the wear resistance of this composite coating. [Copyright &y& Elsevier]

Abstract: In this study, the influence of YPSZ/CeO2 on the surface performance of the laser-cladded composites was firstly researched. Laser cladding of the Fe3Al/Co42B+YPSZ/CeO2 pre-placed powders on Ti–6Al–4V alloy can form the composite coating, which increased the wear resistance of the substrate. With addition of 20wt.%TiC, the longevity of the molten pool decreased, leading to the decreasing of the growth time of the precipitates and the content of CoTi, TiNi, AlNi, Ti3Al and TiB phases. The addition of 20wt.%TiC did not improve the tribological properties of the Fe3Al/Co42B+YPSZ/CeO2 laser-cladded composite coating. [Copyright &y& Elsevier]

Abstract: Specific wear rate of composite materials plays a significant role in industry. The processes to measure it are both time and cost consuming. It is essential to suggest a modeling method to predict and analyze the effectiveness of parameters of specific wear rate. Nowadays, computational methods such as Artificial Neural Network (ANN), Fuzzy Inference System (FIS) and adaptive neuro-fuzzy inference system (ANFIS) are mainly considered as applicable tools from modeling point of view. ANFIS present integrate performance of neural network (NN) and fuzzy system (FS). Present paper investigates performance prediction of a specific wear rate of epoxy composites with various composition using ANFIS. The obtained results showed that ANFIS is a powerful tool in modeling specific wear rate. The obtained mean of squared error (MSE) for testing sets in present paper obtained 0.0071. [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: Polyetheretherketone (PEEK) composites reinforced with carbon fibers (CFs) and nano-ZrO2 particles were prepared by incorporating nanoparticles into PEEK/CF composites via twin-screw extrusion. The effects of nanoparticles on the mechanical and wear properties of the PEEK/CF composites were studied. The results showed that the incorporation of nano-ZrO2 particles with carbon fiber could effectively enhance the tensile properties of the composites. The tensile strength and Young’s modulus of the composites increased with the increasing nano-ZrO2 content. The enhancement effect of the particle was more significant in the hybrid reinforced composites. The compounding of the two fillers also remarkably improved the wear resistance of the composites under water condition especially under high pressures. It was revealed that the excellent wear resistance of the PEEK/CF/ZrO2 composites was due to a synergy effect between the nano-ZrO2 particles and CF. CF carried the majority of load during sliding process and prevented severe wear to the matrix. The incorporation of nano-ZrO2 effectively inhibited the CF failures through reducing the stress concentration on the carbon fibers interface and the shear stress between two sliding surfaces. It was also indicated that the wear rates of the hybrid composites decreased with the increasing applied load and sliding distance under water lubrication. And low friction coefficient and low wear rate could be achieved at high sliding velocity. [Copyright &y& Elsevier]

Abstract: Atmospheric pressure filamentary dielectric barrier discharge (APDBP) treatment was adopted to modify the surface of the multi-walled carbon nanotubes (MWCNTs), altering the miscibility of MWCNTs with bismaleimide (BMI) matrix and the effects of this treatment on friction and wear properties of MWCNTs/BMI composites were investigated. Dynamic mechanical analysis (DMA), scanning electron microscope (SEM) images of the fractured surface and the worn surface were adopted to figure out the possible friction and wear mechanism of the composite. It is found that BMI composite with APDBD treated MWCNTs exhibits a lower friction coefficient value and a lower wear loss rate value than the composite with original MWCNTs, which can be related to the higher degree of crosslink of the resin and also better interfacial adhesion between MWCNTs and the BMI matrix. [Copyright &y& Elsevier]