Fibridization Effect on the Mechanical Behavior of PA66/PTFE Blend Based Fibrous Composites

The use of natural fiber along with the glass fiber in polymer composites is one of the present material combinations for automotive industries. This article deals with the hybrid effect of 10 wt% short glass fibers (SGF) and 10 wt% short basalt fibers (SBF) on the mechanical behavior of 80 wt% PA66/20 wt% Teflon (PA66/PTFE) blend. These composite materials were prepared by melt mixing method, by using twin screw extruder followed by injection molding. The mechanical performance of the composite materials was tested as per ASTM method. The experimentally determined mechanical properties were tensile behavior, flexural behavior and impact behavior. Hardness and density of the blended composites were also studied. Experimental results revealed that the effect of hybrid short fibers on the blend greatly enhanced the mechanical behavior. Increase in tensile strength and flexural strength by 33% and 57% respectively and 6% reduction in elongation was exhibited by the blend due to the hybrid effect of fibers. The synergistic effect between the fibers and the matrix blend improved the mechanical behavior. The strain rate of the hybrid composites was deteriorated due to the hybrid effect. The enhancement of load carrying capacity by 17.35, 8.5 and 36% was exhibited by SGF, SBF and hybrid fiber filled PA66/PTFE blend composites respectively. The impact strength of the hybrid composites was reduced due to the brittle nature of the hybrid filled composites. Fiber fracture, fiber pull out and fiber misalignment were the certain mechanisms observed during mechanical performance. The fractured surfaces were analyzed through Scanning Electron Microscopy photographs.     

Influence of Experimental Parameters on Friction and Wear Mechanisms of PA66/PTFE Blend Reinforced with Glass Fiber

Polymer blend of composition 80 wt% polyamide 66/20 wt% polytetraflurotheylene (PA66/PTFE) was selected as a matrix and reinforced with different weight percentage of short glass fibers (SGF). These composites were prepared by melt mix method using twin screw extruder followed by injection molding. The tribological behaviors were tested by using pin on disc machine by varying the different experimental parameters. The friction and wear mechanisms were studied as a function of sliding velocity, sliding load, and distance. The effect of fiber loading lowered the wear volume loss of SGF filled PA66/PTFE blend. The least frictional coefficient of 0.24 was obtained for 20 wt% of SGF in the blend. However, the wear resistance was not apparently improved by SGF loading in the experimental range for comparison with unfilled PA66/PTFE blend. The worn surfaces of specimen were examined by scanning electron microscopy photographs. The observations revealed that the frictional behavior was a function of development and formation of transfer film. Matrix wear and fiber wear were the result of frictional mechanism. The critical wear volume of PA66/PTFE/SGF composites was the contribution of both matrix and fiber wear. The abrasive nature of SGF was also one of the important factor for frictional behavior.     

Effect of Short Glass Fiber Loading on the Mechanical Behaviour of PA66/PTFE Blend Composites

The polymer blend of Polyamide66 and Polytetrafluroethylene (PA66/PTFE) (80/20 wt.%) were selected for the study. These blends were reinforced with 5, 10, 15, 20, 25 and 30 wt.% of silane treated short glass fibers (SGF) and were prepared by using melt mixing method with the help of twin screw extruder. The mechanical properties such as tensile strength, flexural strength, impact strength were studied in addition to hardness of the blend composites as per ASTM. The results revealed that the addition of SGF into PA66/PTFE blend greatly enhanced the mechanical properties of the polymer blend. The tensile strength and the flexural strength of the blend was almost double than that of the neat blend after reinforcing 30 wt.% of SGF. The addition of SGF into the blend greatly improved the flexural modulus and also the hardness of the blend. The impact strength of the blend decreased initially and then increased after the SGF addition into the blend. The density of PA66/PTFE blend increased after SGF addition. The strain at break almost remained constant but deflection due to bending decreased with the addition of SGF into the studied polyblend. However, the effect of higher loading of SGF on the mechanical behavior of PA66/PTFE blend was greatly appreciable. The fractured surfaces of the specimens were examined by using Scanning Electron Microscope photographs (SEM).     

Combined Effect of Micro Fillers on the Mechanical and Fracture Behavior of Polyamide 66 and Polypropylene (PA66/PP) Blend

The combinative effect of Micro fillers on the 80/20 wt% of Polyamide 66 and Polypropylene blend (PA66/PP) is studied. Three composites prepared by reinforcing micro fillers of Molybdenum disulphide (MoS₂) (PA66/PP/MoS₂), Silicon carbide (SiC) (PA66/PP/MoS₂/SiC) and Alumina (Al₂O₃) (PA66/PP/MoS₂/SiC/Al₂O₃) of, having different geometric shapes. The mechanical properties studied are tensile strength, flexural strength, impact strength including the hardness of the blend micro composites as per ASTM methods. The fracture toughness at different temperatures of the composites is studied as per ASTM. Results reveal that the combined effect of hybrid micro fillers decreases the mechanical behavior of PA66/PP blend composites. The poorest mechanical properties are obtained when SiC is incorporated into the MoS₂ filled blend PA66/PP composites. The appreciable increase in the mechanical properties is noticed by the addition of Al₂O₃ into the hybrid filled PA66/PP blend composites. Though the effect of SiC addition to PA66/PP/MoS₂ composites increases the impact strength appreciably but decreasing trend is also observed due to the hybrid effect of three fillers. But the differently shaped micro fillers exhibit a synergic effect on the tensile and flexure properties of PA66/PP based composites respectively. The density of the studied blend increases due to denser nature of micro fillers. The hardness of the blend is increased by 18 % by the addition of micro fillers as against the blend PA66/PP. The increase in fracture toughness by 188 % is exhibited by the hybrid effect of micro fillers as against the neat blend at room temperature. Among these micro composites, PA66/PP/MoS₂/SiC/Al₂O₃ has shown superior mechanical properties when compared to individual effect of the fillers on the blend. The fractured surfaces are studied by using scanning electron microscope photographs.     

Investigation of Mechanical Properties and Dry Sliding Wear Behaviour of Squeeze Cast LM6 Aluminium Alloy Reinforced with Copper Coated Short Steel Fibers

LM6 aluminium alloy with 2.5–10 wt% of copper coated short steel fiber reinforced composites were prepared using squeeze casting process. Microstructure and mechanical properties viz., hardness, tensile strength and ductility were investigated. Dry sliding wear behaviour was tested by considering sliding distance and load. Fracture surface and worn surface were examined using field emission scanning electron microscope (FESEM). Hardness of composites increased with increasing wt% of fiber. Tensile strength of composites increased up to 19% for 5 wt% fiber composites. Further addition of fibers decreased the tensile strength of composites. Ductility of the composites decreased with the addition of fibers into the matrix. Wt% of fibers significantly decreased the weight loss, coefficient of friction and wear rate. Also the cumulative weight loss decreased up to 57% for 10 wt% of composites compared to LM6 aluminium alloy. Fracture surface of composite tensile specimen showed dimple formation and fiber pullout. Worn surface of matrix showed long continuous grooves due to local delamination on the surface. However, worn surface of composites showed fine and smooth grooves due to ploughing rather than local delamination. Copper coated steel fiber reinforcement in LM6 aluminium alloy exhibited better mechanical properties and wear resistance compared to matrix.     

Investigation on microstructure and tensile behaviour of stir cast LM13 aluminium alloy reinforced with copper coated short steel fibers using response surface methodology

Copper coated steel fibers reinforced LM13 aluminium alloy composites have been prepared using stir casting process. Experiments have been designed using response surface methodology by varying wt% of reinforcement (0–10), stirrer speed (350–800 rpm) and pouring temperature (700–800 °C). Microstructure, tensile strength and fracture surface of composites have been investigated. Analysis of variance, significance test and confirmation tests have been performed and regressions models have been developed to predict the tensile strength of composites. Response surface plots reveal that tensile strength of composites increases with increasing wt% of copper coated steel fibers reinforcement up to 6 wt%. Further increase in wt% of steel fibers decreases the tensile strength of composites. However tensile strength of composites increases with increasing stirrer speed due to the uniform and homogeneous dispersion of steel fibers in matrix. Optimum stir cast process parameters for obtaining higher tensile strength are found to be 5.9 wt% of reinforcement, 753 °C pouring temperature and stirrer speed of 633 rpm. Fracture mechanism is dominated by steel fiber pullouts in composites with higher wt% of reinforcement and dimples are observed in the surface of composites containing lower levels of wt% of reinforcement.     

Mechanical Properties and Dry Sliding Wear Behaviour of Molybdenum Disulphide Reinforced Zinc–Aluminium Alloy Composites

ZA-27 alloy is a lightest alloy which offers excellent bearing and mechanical properties in automobile and industrial applications. In this study, the MoS₂ particles with 0.5, 1 and 1.5 (wt%) weight percentages were reinforced in ZA-27 alloy to form composites, which were fabricated by using ultrasonic assisted stir casting method. The ZA-27/MoS₂ composite specimens were examined for chemical composition with the aid of XRD technique and EDS. Microstructure analysis of the ZA-27/MoS₂ composites was studied using SEM. Tests were conducted for mechanical properties such as tensile strength and hardness on ZA-27/MoS₂ composites samples as per ASTM standards. Dry sliding wear behavior of the composites was tested at various operating conditions by using pin-on-disc apparatus. Microstructural images of the ZA-27 composites reveal that there is a uniform dispersion of the MoS₂ particles in the base material. From the results it is observed that the mechanical properties increases with ZA-27 reinforced with 0.5 wt% MoS₂ composite and further decreases with increase in the filler content. The enhanced wear resistance is observed in ZA-27 reinforced MoS₂ composites as compared to the unreinforced alloy. The wear rate of the ZA-27 composites decreases with the increase in filler content, further the worn surfaces as examined using SEM reveals the wear mechanism explaining the improved wear resistance of the particulate composites.     

Mechanical Properties and Tribological Behavior of Al6061–SiC–Gr Self-Lubricating Hybrid Nanocomposites

In the present investigation, a newly fabricated Al6061 reinforced with various quantity (0.4–1.6 wt%) of nano SiC in steps of 0.4 and fixed quantity (0.5 wt%) of micro graphite particle’s hybrid nanocomposites were prepared by ultrasonic assisted stir casting method. The influence of nano SiC and graphite content on the mechanical and tribological properties of Al6061 hybrid nanocomposites were studied. The pin-on-disc equipment was used to carry out experiment at 10–40 N applied load, 0.5 m/s sliding speed and 1000 m sliding distance. The Al/SiC/Gr hybrid nano-composite and matrix alloy wear surfaces were characterized by FESEM equipped with an EDS, 3D profilometer to understand the wear mechanisms. The results of Al/SiC/Gr self-lubricating hybrid nano-composites showed improved wear resistance than the Al6061 matrix alloy. The co-efficient of friction of Al/SiC/Gr hybrid nano-composites were lower than those of the unreinforced alloy at various applied load. Compared to matrix alloy, the surface roughness of Al/SiC/Gr hybrid nano-composites had significantly reduced to 66% at low load and 75% at high load. Self-lubricating Al/SiC/Gr hybrid nanocomposites showed superior surface smoothness compared to matrix alloy.     

Effect of rare earths surface treatment on tribological properties of carbon fibers reinforced PTFE composite under oil-lubricated condition

The effect of rare earths （RE） surface treatment of carbon fibers （CF） on tribological properties of CF reinforced polytetrafluoroethylene （PTFE） composites under oil-lubricated condition was investigated. Experimental results revealed that RE treated CF reinforced PTFE （CF/PTFE） composite had the lowest friction coefficient and wear under various applied loads and sliding speeds compared with untreated and air-oxidated composites. X-ray photoelectron spectroscopy （XPS） study of carbon fiber surface showed that, after RE treatment, oxygen concentration increased obviously, and the amount of oxygen-containing groups on CF surfaces were largely increased. The increase in the amount of oxygen-containing groups enhanced interfacial adhesion between CF and PTFE matrix. With strong interfacial adhesion of the composite, stress could be effectively transmitted to carbon fibers; carbon fibers were strongly bonded with VITE matrix, and large scale rubbing-off of PTFE be prevented, therefore, tribological properties of the composite was improved.     

纤维分散对C/C-SiC复合材料力学性能的影响

利用温压-原位反应法制备短炭纤维增强C/C-SiC复合材料,研究纤维分散对复合材料力学性能的影响.结果表明: 利用分散短炭纤维制备的C/C-SiC复合材料,其抗弯强度和抗压强度分别达到56.6MPa和89.3MPa.该材料纤维之间孔隙少,纤维与基体接合界面多,弯曲时有纤维拔出,为假塑性断裂行为.压缩时无纤维拔出,为脆性断裂行为.最后,利用LI V C提出的束丝数学模型证明了纤维分散有利于提高C/C-SiC复合材料的力学性能.     

Mechanical property and fracture behavior of squeeze-cast Mg matrix composites

The present study aims to investigate the microstructure and fracture properties of AZ91 Mg matrix composites fabricated by the squeeze-casting technique, with variations in the reinforcement material and applied pressure. Microstructural and fractographic observations, along with in situ fracture tests, were conducted on three different Mg matrix composites to identify the microfracture process. Two of them are reinforced with two different short fibers and the other is a whisker-reinforced composite. From the in situ fracture observation of Kaowool-reinforced composites, the effect of the applied pressure on mechanical properties is explained using a competing mechanism: the detrimental effects of fiber breakage act to impair the beneficial effects of the grain refinement and improved densification as the applied pressure increases. On the other hand, for the composites reinforced with Saffil short fibers, microcracks were initiated mainly at the fiber/matrix interfaces at considerably higher stress intensity factor levels, while the degradation of fibers was not observed even in the case of the highest applied pressure. This finding indicates that the higher applied pressure yields better mechanical properties, attributable to the Saffil short fibers having relatively high resistance to cracking. Although an improved microstructure was obtained by accommodating the appropriate applied pressure in the short fiber-reinforced composites, their mechanical properties were far below those of conventional A1 matrix composites. In this regard, the Alborex aluminum borate whisker is suggested as a replacement for the short fibers used in the present investigation, to achieve better mechanical properties and fracture toughness.     

Evaluation of Tribological Performance of PTFE Composite Filled with Rare Earths Treated Carbon Fibers under Water-Lubricated Condition

Carbon fibers （CFs） were surface treated with air-oxidation, rare earths （RE） after air-oxidation, and rare earths, respectively. Erichsen test was conducted to study the interfacial adhesion of PTFE composites filled with carbon fibers treated with different treatment methods. Tribological properties of the PTFE composites, sliding against GCr15 steel under water-lubricated condition, were investigated on a reciprocating ball-on-disk UMT-2MT tribometer. The worn surfaces of the composites were examined using scanning electron microscopy. Experimental results reveal that RE treatment is superior to air oxidation in promoting tribological properties of CF reinforced PTFE （CF/PTFE） composite. The friction and wear properties of PTFE composite filled with RE treated CF are the best of the PTFE composites. RE treatment is more effective than air oxidation to improve the tribological properties of CF/PTFE composite owing to the effective improvement of interfacial adhesion between carbon fibers and PTFE matrix.     

Processing and Evaluation of Mechanical Properties of Sugarcane Fiber Reinforced Natural Composites

In the present work, the natural composites based on sugarcane bagasse fiber and/or coconut shell powder were processed using hand lay-up technique. The matrix selected was polyester. Three different types of composites were considered: polyester matrix + sugarcane fiber, polyester matrix + sugarcane fiber + metal mesh and polyester matrix + sugarcane fiber + coconut shell filler. The sugarcane fibers were used in three forms: (1) chemically treated by NaOH, (2) chemically treated by HCl, and (3) untreated condition. In total, 9 types of composites were developed and studied for tensile, flexural and impact properties. The fracture surface of the tensile and flexural test samples was examined with the aid of scanning electron microscope to understand the bonding characteristics and the mode of failure. The key-findings from the present work are: (1) the composites reinforced with the NaOH treated sugarcane fiber and the metal mesh show superior tensile and impact properties whereas the composites reinforced with the NaOH treated sugarcane fiber show the best flexural properties, (2) NaOH treatment of sugarcane fibres has a significant effect in improving the mechanical properties by surface modification of fibres through OH^? functional groups. In contrast, HCl treatment of sugarcane deteriorates the surface of the sugarcane by absorbing the electrons. The damaged surface results in weak bonding causing poor mechanical properties, (3) From the SEM analysis of the surface of the sugarcane fiber, it may be concluded that the surface condition of the sugarcane fibres decide the bonding with the matrix. The fiber pull-outs and porosities are less in the NaOH treated sugarcane reinforced composites. The fiber failure is the main mechanism of failure in the tensile test whereas the fiber debonding from the matrix is the main source of failure in the flexural test.     

Effect of Rare Earths on Tribological Properties of Carbon Fibers Reinforced PTFE Composites

Carbon fibers （CF） were surface treated with air-oxidation and rare earths （RE）, respectively. The effect of RE surface treatment on tensile strength and tribological properties of CF reinforced polytetrafluoroethylene （PTFE） composites was invest/gated. Experimental results revealed that RE was superior to air ox/dation in improving the tensile strength, elongation, and the tensile modulus of CF reinforced PTFE （CF/PTFE） composite. Compared to the untreated and air-oxidated CF/PTFE composite, the RE treated composite had the lowest friction coefficient and specific wear rate under a given applied load and reciprocating sliding frequency. The RE treatment effectively improved the interfacial adhesion between CF and PTFE. With strong interfacial coupling, the carbon fibers carried most of the load, and direct contact and adhesion between PTFE and the counterpart were reduced, accordingly the friction and wear properties of the composite were improved.     

Tribological Behavior of SiC Particulate Reinforced AA5754 Matrix Composite Under Dry and Lubricated Conditions

The present work dealt with an investigation on tribological behavior of AA5754 matrix reinforced with 10 wt% SiC particles composite by using a pin on disc machine. Sliding tests were conducted under dry and oil lubricated conditions against hardened DIN 100Cr6/EN31 steel counter surface. Wear rates of the matrix alloy and the metal matrix composite (MMC) were measured over load of 100 N under a speed of 4.71 m/s. Detailed scanning electron, optical microscopy analyses were undertaken to clarify the effect of SiC particles on tribological behavior. SiC reinforced AA5754 alloy exhibited lower wear rate than unreinforced alloy.     

Physical and Mechanical Behaviour of <Emphasis Type="Italic">Sida acuta</Emphasis> Fibre Reinforced Epoxy Composite at Different Fibre Loading

Sida acuta is the botanical name of the plant belonging to Malvaceae family. Sida acuta fibres are available in nature, relatively low cost and abundantly available in India. The present work has been carried out to make use of Sida acuta fibres in the fibre reinforced polymer composites. In this study the composites are made using untreated bidirectional Sida acuta stem fibre as reinforcement and commercially available epoxy resin as matrix material using hand lay-up technique. The composites are made of different fibre fabric orientation (0°/90° and ±?45°) and each fabric orientation composite with different fibre loading (0, 24, 28 and 32 wt%) are characterized for their physical and mechanical properties. The test results show the significant effect of fibre loading on the physical and mechanical properties of these composites. Also the fracture behaviour and fibre pull-out at the fracture of the composite samples have been analysed using scanning electron microscope.     

Statistical Analysis of Tribological Properties of Aluminum Matrix Composites Using Full Factorial Design

This work describes the tribological properties of mono AA6061-10 wt% B₄C and hybrid AA6061-10 wt% B₄C-7.5 wt% Gr composites which could be used as a potential substitute for aluminum alloys used in automotive engines. The tribological experiments are performed as per the experimental scheme designed using full factorial design. The results suggest that the wear loss increases with applied load and sliding distance and the friction coefficient increases with increase in applied load. Further, the ANOVA analysis reveals the statistically and physically significant factors which influence the wear loss and friction coefficient. Formation of Gr-rich tribolayer causes reduction in the wear loss and friction coefficient for hybrid composites compared to the mono ones.     

Tensile and fatigue behavior of Al-based metal matrix composites reinforced with continuous carbon or alumina fibers: Part I. Quasi-unidirectional composites

The thermomechanical (dilatometric, tensile, and fatigue) behavior of Al-based metal matrix composites (MMCs) is investigated. These composites are reinforced by quasi-unidirectional (quasi-UD) woven fabric preforms with 90 pct of continuous fibers in the longitudinal direction and 10 pct in the transverse direction. The two composite systems investigated feature a highly ductile matrix (AU2: Al-2Cu wt pct) with a strongly bonded fiber-matrix interface (N610 alumina fibers) and an alloyed, high-strength matrix (A357: Al-7Si-0.6Mg wt pct) with a weak fiber-matrix interface (K139 carbon fibers). Microstructural investigation of the tested specimens has permitted identification of the specific characteristics of these composites: undulation of the longitudinal bundles, presence of the straight transverse bundles, interply shearing, and role of brittle phases. Moreover, simple semiquantitative models (e.g., interply shearing) have enabled explanation of the specific mechanical behavior of these quasi-UD composites, which exhibit high tensile and fatigue strengths, as compared with the corresponding pure UD composites. Knowledge of the specific characteristics and mechanical behavior of these quasi-UD composites will facilitate the further investigation of the (0, ±45, 90 deg) quasi-UD laminates (Part II). At a more theoretical viewpoint, the specific geometry and behavior of these quasi-UD composites allows exacerbation of fatigue mechanisms, even more intense than in “model” composites.     

Reaction Kinetics at the Fiber/Matrix Interface of SiC<Subscript>f</Subscript>/Ti–15–3 Composites

In the current research work, spark plasma consolidated beta-titanium alloy Ti–15V–3Cr–3Al–3Sn composites reinforced with SiC fibers (Sigma SM1240) were subjected to high temperatures (1173, 1223 and 1273 K) for different time periods (2.7, 11, 25 and 44 h) to investigate the kinetics of the chemical reactions at the fiber/matrix interface. Through microstructural studies and room temperature tensile tests, we have attempted to study the effect of the formed brittle reaction zone on the final mechanical properties of the composite. We have observed that, prior to the SiC fiber, the protective carbon coating reacts with the matrix and results in the formation of a reaction zone (predominantly TiC) at the fiber/matrix interface. The reaction zone propagates into the matrix with increase in time at the expense of the carbon coating, and finally ends with the onset of titanium silicide reaction. The reaction kinetics at the fiber/matrix interface was predominantly controlled by diffusion of carbon through the reaction zone and the activation energy for the same was calculated to be 149 kJ/mol. It was clear from the tensile test results that the mechanical properties of the composites do not earnestly decrease until the commencement of titanium silicide reaction.     

Crack Growth Resistance of Hybrid Fiber-Reinforced Cement Matrix Composites

The effect of hybrid fiber reinforcement on fracture energy and crack propagation in cement matrix composites is examined. The crack in cement matrix composites is allowed to fracture under mode-I loading with three-point bending beam specimens. The influence of fiber types and their combination is quantified by using the toughness index and fracture energy. A proper hybrid combination of steel fibers and polyvinyl alcohol microfibers enhances the resistance to both the nucleation and growth of the crack. The micromechanical model of hybrid composites by using a fiber bridging law is emphasized, and the numerical model prediction closely matches the behavior obtained from the experiment. The influencing role of the material parameters in the fracture tests (e.g., the fracture toughness index and fracture energy) becomes more apparent than ones used in some conventional strength-based or fiber pullout tests, and these fracture parameters could screen the effect of fiber/microfiber reinforcement in enhancing the crack growth resistance of cementitious composites. This study demonstrates that fundamental fracture tests are effective to characterize and develop high-performance hybrid fiber–reinforced cement matrix composites.