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.     

Hybridization Effect on the Mechanical Behavior of Monophase Reinforced PA66/Teflon Blend Based Hybrid Thermoplastic Composites

The Monophase reinforced hybrid thermoplastic composites are the materials for the superior mechanical behavior. This article deals with the effect of single reinforcing phase (Fiber) in hybrid mode on the mechanical behavior of PA66/Teflon blend. Two hybrid material systems were selected: 10 wt% short glass fibers (SGF) and 10 wt% short carbon fibers reinforced 80 wt% PA66/20 wt% Teflon (PA66/PTFE) blend (GB) and 10 wt% SGF and 10 wt% short basalt fibers reinforced 80 wt% PA66/20 wt% Teflon (PA66/PTFE) blend(GB). These hybrid composite materials were prepared by melt mixing method by using twin screw extruder followed by injection molding. The experimentally determined mechanical properties were tensile behavior, flexural behavior and impact behavior. Experimental results revealed that addition of hybrid short fibers into the blend greatly enhanced the mechanical behavior of PA66/PTFE composites. Increase in tensile strength by 46 and 33%, flexural strength by 45 and 57% for GC and GB composites respectively were observed. The GC composites had the better impact strength than GB composites. The peak load obtained was 36 and 48% higher than that of neat blend for GC and GB composites respectively were observed. The strain rate of the hybrid composites deteriorated due to the hybrid effect. The synergistic effect between the fibers and the matrix blend improved the mechanical behavior. The hybrid effect increased the size of the voids and also the number of aggregates of the short fibers. This would weaken the reinforcement effect simultaneously building the strong bridge for the development of internal crack. Fractured surfaces were observed through Scanning Electron Microscopy photographs.     

Artificial Neural Network Modeling of Mechanical Properties of Calcium Carbonate Impregnated Coir-Polyester Composites

The tensile, flexural and impact properties of calcium carbonate particles-impregnated coir fiber-reinforced polyester composites were evaluated. The short untreated green husk coir fibers were used as reinforcement materials in unsaturated polyester resin matrix. The composite fabrications were planned with the three levels of fiber parameters namely fiber length, fiber diameter and filler content as per design of experiments (DOE) and the mechanical properties were tested as per ASTM standards. An artificial neural network (ANN) model was developed to predict the mechanical properties and it was observed that the developed ANN model accurately predicted the mechanical properties within the ranges specified.     

Flexural Behavior of R/C Beams Strengthened with Carbon Fiber Reinforced Polymer Sheets or Fabric

Their resistance to electro-chemical corrosion, high strength-to-weight ratio, larger creep strain, fatigue resistance, and nonmagnetic and nonmetallic properties make carbon fiber reinforced polymer (CFRP) composites a viable alternative to bonding of steel plates in repair and rehabilitation of reinforced concrete structures. The objective of this investigation is to study the effectiveness of externally bonded CFRP sheets or carbon fiber fabric in increasing the flexural strength of concrete beams. Four-point bending flexural tests were conducted up to failure on nine concrete beams strengthened with different layouts of CFRP sheets and carbon fiber fabric and on three beams with different layouts of anchored CFRP sheets. An analytical procedure, based on compatibility of deformations and equilibrium of forces, was presented to predict the flexural behavior of beams strengthened with CFRP sheets and carbon fiber fabric. Comparisons were made between the test results and the analytical calculations. The flexural strength was increased up to 58% on concrete beams strengthened with anchored CFRP sheets.     

纤维类型和涂层对纤维增强MoSi2复合材料弯曲性能的影响

以短切碳纤维(Cf)和碳化硅纤维(SiCf)为增强相,并用化学气相渗透法对部分纤维进行炭涂层处理,采用热压法制备了4种纤维增强MoSi2基复合材料(SiCf-MoSi2、SiCf/C-MoSi2、Cf-MoSi2和Cf/C-MoSi2),研究了纤维类型及表面炭涂层对MoSi2基复合材料弯曲性能的影响.结果表明纤维的加入明显提高了MoSi2的抗弯强度,加入5%SiCf和5%Cf的复合材料的强度比纯MoSi2分别提高了9.0%和22.8%,Cf增强作用明显优于SiCf;纤维类型相同时,具有炭涂层的纤维增强效果更显著,5%Cf/C-MoSi2复合材料的强度最高,达到了364.7MPa,比纯MoSi2的强度提高了30%;扫描电镜分析表明,无炭涂层的SiCf与MoSi2基体间存在着明显的裂缝,炭涂层改变了纤维与基体的界面结合;有涂层纤维的断裂机制为首先脱粘然后拔出.     

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.     

Materials characterization of silicon carbide reinforced titanium (Ti/SCS-6) metal matrix composites: Part I. Tensile and fatigue behavior

Flexural fatigue behavior was investigated on titanium (Ti-15V-3Cr) metal matrix composites reinforced with cross-ply, continuous silicon carbide (SiC) fibers. The titanium composites had an eightply (0, 90, +45, -45 deg) symmetric layup. Fatigue life was found to be sensitive to fiber layup sequence. Increasing the test temperature from 24 °C to 427 °C decreased fatigue life. Interface debonding and matrix and fiber fracture were characteristic of tensile behavior regardless of test temperature. In the tensile fracture process, interface debonding between SiC and the graphite coating and between the graphite coating and the carbon core could occur. A greater amount of coating degradation at 427 °C than at 24 °C reduced the Ti/SiC interface bonding integrity, which resulted in lower tensile properties at 427 °C. During tensile testing, a crack could initiate from the debonded Ti/SiC interface and extend to the debonded interface of the neighboring fiber. The crack tended to propagate through the matrix and the interface. Dimpled fracture was the prime mode of matrix fracture. During fatigue testing, four stages of flexural deflection behavior were observed. The deflection at stage I increased slightly with fatigue cycling, while that at stage II increased significantly with cycling. Interestingly, the deflection at stage III increased negligibly with fatigue cycling. Stage IV was associated with final failure, and the deflection increased abruptly. Interface debonding, matrix cracking, and fiber bridging were identified as the prime modes of fatigue mechanisms. To a lesser extent, fiber fracture was observed during fatigue. However, fiber fracture was believed to occur near the final stage of fatigue failure. In fatigued specimens, facet-type fracture appearance was characteristic of matrix fracture morphology. Theoretical modeling of the fatigue behavior of Ti/SCS-6 composites is presented in Part II of this series of articles. This article is based on a presentation made in the symposium entitled “Creep and Fatigue in Metal Matrix Composites” at the 1994 TMS/ASM Spring meeting, held February 28–March 3, 1994, in San Francisco, California, under the auspices of the Joint TMS-SMD/ASM-MSD Composite Materials Committee.     

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).     

Tensile Properties of Surface-Treated Glass Fiber Reinforced PTFE Composite with Rare Earth Elements

The optimum amount of rare earth elements (RE) for treating glass fiber surface and its effect on the tensile properties of glass fiber reinforced polytetrafluoroethylene (GF/PTFE) composites were investigated. The tensile properties of GF/PTFE composites with different surface treatment conditions were measured. The fracture surface morphologies were observed and analyzed by SEM. The results indicate that rare earth elements can effectively promote the interfacial adhesion between the glass fiber and PTFE, owing to the effects of rare earth elements on the compatibility. The tensile properties of GF/PTFE composites can be improved considerably when the content of RE in surface modifier is 0.2%-0.4%,and the optimum performance of GF/PTFE composites is obtained at 0.3 % RE content.     

苎麻纤维增强聚乳酸复合材料性能研究

通过密炼?注塑成型工艺制备了不同苎麻纤维含量的聚乳酸基复合材料,研究了纤维含量对复合材料性能的影响规律,并揭示了纤维增强机理。研究表明,苎麻纤维的添加提高了复合材料的耐热性能,尤其是当纤维质量分数为40%时,复合材料的热变形温度提高了10.5%。此外,苎麻纤维均匀地分散在基体中,由于纤维与聚乳酸的界面强度较弱,断面上有大量的纤维拔出和纤维孔洞;差示扫描量热仪测试表明高含量的纤维限制了聚乳酸分子链的运动,促进复合材料形成更加致密完善的晶核;同时,流变行为也表明苎麻纤维含量的增加有助于提高复合材料的黏弹响应和复合黏度;最后,苎麻纤维的加入提高了复合材料的拉伸和弯曲强度,且随纤维含量的增加而增大。与聚乳酸相比,当纤维质量分数为40%时复合材料的拉伸和弯曲强度分别提高了30%和21.9%。      

Effect of Copper Coating and Reinforcement Orientation on Mechanical Properties of LM6 Aluminium Alloy Composites Reinforced with Steel Mesh by Squeeze Casting

Uncoated and copper coated steel wire mesh reinforcing LM6 aluminium alloy composites have been produced using squeeze casting process by varying reinforcement orientation viz., 0°, 45° and 90° respectively. Microstructure of the castings has been examined and mechanical properties such as hardness, tensile strength and ductility have been investigated. Fracture surface of tensile specimens has been analysed using field emission scanning electron microscope. Microstructure of samples reveals that copper coating on steel wires improves the interface bonding between matrix and reinforcement. Average hardness values of 259 and 90 Hv have been observed in steel wire and matrix respectively. Tensile strength of composites increases with increasing angle of reinforcement orientation from 0° to 90°. Tensile strength increases up to 11% by reinforcing copper coated steel wire mesh at 90° orientation as compared to LM6 aluminium alloy. Fracture surface of composites shows pullout of steel wires in uncoated steel wire mesh composites and broken wires in copper coated steel wire mesh composites respectively. Dimples have been observed on the fracture surface of LM6 aluminium alloy. In general, copper coated steel wire mesh composites offer better hardness and tensile strength compared to uncoated steel wire mesh composites and LM6 aluminium alloy. This may be attributed to the copper coating on steel wires which results better interface bonding between matrix and reinforcement.     

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.     

Determination of tensile,flexural properties and microstructural characterization of calcium carbonate filler reinforced polypropylene matrix composites

Calcium carbonate is one of the commonly used inorganic filler reinforcements in polypropylene matrix. In this research work, granules of chicken egg shell containing natural organic calcium carbonate resource has been introduced to reinforce in the polypropylene base material. The aim of this experimental study is to determine the tensile, flexural properties and to characterize the microstructures of granular chicken shell containing natural calcium carbonate reinforced in polypropylene. Chicken egg shells are crushed and sieved and granules of size 160μm are selected for reinforcement in the polypropylene matrix. The granules are then mixed with polypropylene base material with silane as a coupling agent proportionally in order to obtain four different proportions 10%, 20%, 30% and 40% on weight fraction basis with the aid of an extrusion machine. Experimental result have shown improvements in Tensile Modulus and Flexural Modulus of this newly processed natural organic calcium carbonate filler reinforced polypropylene composites, although it has not improved the tensile strength, flexural Strength and strain to fracture. The weight fraction ratio of the filler reinforced in the matrix which gave the highest tensile and flexural modulus is 20% and 10%, respectively.     

Diffusion Bonding of Microduplex Stainless Steel and Ti Alloy with and without Interlayer: Interface Microstructure and Strength Properties

The interface microstructure and strength properties of solid state diffusion bonding of microduplex stainless steel (MDSS) to Ti alloy (TiA) with and without a Ni alloy (NiA) intermediate material were investigated at 1173 K (900 °C) for 0.9 to 5.4 ks in steps of 0.9 ks in vacuum. The effects of bonding time on the microstructure of the bonded joint have been analyzed by light optical microscopy and scanning electron microscopy in the backscattered mode. In the direct bonded joints of MDSS and TiA, the layer-wise σ phase and the λ + FeTi phase mixture were observed at the bond interface when the joint was processed for 2.7 ks and above holding times. However, when NiA was used as an intermediate material, the results indicated that TiNi₃, TiNi, and Ti₂Ni are formed at the NiA-TiA interface, and the irregular shaped particles of Fe₂₂Mo₂₀Ni₄₅Ti₁₃ have been observed within the TiNi₃ intermetallic layer. The stainless steel-NiA interface is free from intermetallics and the layer of austenitic phase was observed at the stainless steel side. A maximum tensile strength of ~520 MPa, shear strength of ~405 MPa, and impact toughness of ~18 J were obtained for the directly bonded joint when processed for 2.7 ks. However, when nickel base alloy was used as an intermediate material in the same materials, the bond tensile and shear strengths increase to ~640 and ~479 MPa, respectively, and the impact toughness to ~21 J when bonding was processed for 4.5 ks. Fracture surface observations in scanning electron microscopy using energy dispersive spectroscopy demonstrate that in MDSS-TiA joints, failure takes place through the FeTi + λ phase when bonding was processed for 2.7 ks; however, failure takes place through σ phase for the diffusion joints processed for 3.6 ks and above processing times. However, in MDSS-NiA-TiA joints, the fracture takes place through NiTi₂ layer at the NiA-TiA interface for all bonding times.     

Natural Mallow Fiber-Reinforced Epoxy Composite for Ballistic Armor Against Class III-A Ammunition

Epoxy matrix composites reinforced with up to 30 vol pct of continuous and aligned natural mallow fibers were for the first time ballistic tested as personal armor against class III-A 9 mm FMJ ammunition. The ballistic efficiency of these composites was assessed by measuring the dissipated energy and residual velocity after the bullet perforation. The results were compared to those in similar tests of aramid fabric (Kevlar?) commonly used in vests for personal protections. Visual inspection and scanning electron microscopy analysis of impact-fractured samples revealed failure mechanisms associated with fiber pullout and rupture as well as epoxy cracking. As compared to Kevlar?, the mallow fiber composite displayed practically the same ballistic efficiency. However, there is a reduction in both weight and cost, which makes the mallow fiber composites a promising material for personal ballistic protection.     

Studies on Effect of Parent Metal Condition on the Room Temperature Mechanical Properties of Ti6Al4V Friction Welds

The influence of parent metal condition on the microstructure and mechanical properties of friction welds of Ti6Al4V alloy has been investigated. Welds are observed to contain predominantly martensite. Stress relieving results in improvement in the strengths of α + β and β treated parent metal and their welds. β welds are observed to contain coarser prior β grains. Studies reveal that welds of α + β solution treated parent metal exhibit higher strength than all the other welds. In plain tensile tests, the location of failure is away from the welds in all the conditions, suggesting that the welds are stronger than their respective parent metals. Parent metal in α + β and β solution treated conditions is observed to respond to stress relieving such that, hardness is improved after stress relieving. Stress relieving results in reduced ductility and improvement in the strength of the welds. Notch tensile strength of the welds is observed to be higher than their parent metals and stress relieving results in further improvement. The notch tensile ratio of the welds has been observed to be ~1.4 in all the conditions indicating that the welds are not notch sensitive.     

Evaluation of Mechanical Properties and Structure of Al-1100 Composite Reinforced with ZrO<Subscript>2</Subscript> Nanoparticles via Accumulative Roll-Bonding

In this study, aluminum metal matrix composites reinforced with ZrO₂ nano-particles in volume fraction of 0.5, 0.75 and 1 % were manufactured through accumulative roll bonding (ARB) process. The results of composite microstructure indicated excellent ZrO₂ particle distribution in the Al matrix after 10 cycles of ARB process. The X-ray diffraction results also showed that nanostructured Al/ZrO₂ nano-particles composite with the average crystallite size of 48.6 nm was successfully achieved after 10 cycles of ARB process. The tensile tests were conducted on the ARBed strips. The tensile strength increased 2.15 times more than the initial value. The elongation dropped abruptly at the first cycle, and then increased slightly. The SEM images observations from the fracture surface showed that after 10 cycles of ARB process the fracture was almost shear fracture mode with fine and stretched pores.     

Tensile strain-rate sensitivity of

The tensile strain-rate sensitivity of continuous-tungsten-fiber reinforced niobium composites (W/Nb), fabricated by an arc-spray process, was studied in the 1300 to 1600 K temperature range. The tensile properties of the fiber and matrix components, as well as of the composites, were measured and compared to rule of mixtures (ROM) predictions. The deviation from the ROM was found to depend upon the chemistry of the tungsten alloy fibers, with positive deviations for thoria-dispersed W wire (ST300) reinforced Nb composite(i.e., stronger composite strength than the ROM) and negative or zero deviations for lamp-grade W wire (218) reinforced Nb composite. In addition, it was found that the composites tested at higher crosshead speeds exhibited a strain-rate sensitivity greater than that of the free fibers tested at the same crosshead speeds, even though the composite tensile strength is determined mainly by the fiber component.     

Effects of SiCp reinforcement by electroless copper plating on properties of Cu/SiCp composites

Abstract

Silicon carbide reinforced copper matrix composites containing 50–80 vol.-%SiC_p were fabricated by hot pressing copper coated SiC_p powder. The results show that the densification, thermal expansion coefficients, flexural strength, and thermal conductivity of Cu/SiC_p composites reinforced by electroless copper plating and their corrosion resistance in 5%NaCl solution are better than those without electroless plating. Physical properties and flexural strength of the composites decrease with an increase in SiC_p content, whereas the corrosion resistance increases with an increase in SiC_p volume fraction. By observing the fracture surface after a flexural test, it can be seen there are two types of fracture model: the cracking of Cu/SiC_p interface and the pulling out of SiC_p particles. The experiment also proved that the bonding strength of the Cu/SiC_p interface and the pressure of the hot pressing operation are the two main factors which influence the fracture of these composites.