Effect of Al(OH)<Subscript>3</Subscript> Particle Fraction on Mechanical Properties of Particle-Reinforced Composites Using Unsaturated Polyester as Matrix

The effect of particle fraction on mechanical properties of particle-reinforced composites was studied using tensile and hardness testing. Unsaturated polyester (UP) was used as polymer matrix, and aluminum hydroxide as the reinforcing particles. The fracture morphology of tensile samples was observed by scanning electron microscopy (SEM). The results showed that the tensile strength and absorbed energy increased to a maximum at 10% particle content and then decreased. With increasing content of aluminum hydroxide, the elastic modulus increased, and the fracture elongation decreased. The SEM showed that the failure of the Al(OH)₃/UP composites was one of macroscopically brittle fracture. In addition, the study showed that appropriate amount of filler can enhance the surface hardness of Al(OH)₃/UP composite.     

The effect of dispersed paint particles on the mechanical properties of rubber toughened polypropylene composites

The influence of dispersed paint particles on the mechanical properties of rubber toughened PP was investigated. The matrix was basically a hybrid of PP, rubber and talc. Model systems with spherical glass bead filled matrix were also studied to examine the effect of filler shape and size. Properties like tensile strength, strain at break, impact strength, and fracture toughness were influenced by the dispersed inclusions. Tensile strength at yield decreased linearly according to Piggott and Leinder's equation. Strain at break decreased more drastically with paint particles than glass beads, revealing that irregularly shaped particles offered greater stress concentrations. The tensile strength and strain at break were less influenced by the size of paint particles whereas a slight decrease in the modulus values was observed with decreasing particle size. Impact strength and fracture toughness also decreased with increasing filler fraction. Lack of stress transfer between filler and matrix aided in reduction of impact strength. Decrease in fracture toughness was influenced by volume replacement and constraints posed by fillers. The size of paint particles had little effect on the impact strength and fracture properties at the filler concentration levels used in this investigation.     

Effect of particle size and surface treatment on constitutive properties of polyester-cenosphere composites

Cenospheres (hollow, aluminum silicate spheres ranging from 10 to 400 m in diameter) are used as filler in a homogeneous polyester composite. Particle size was varied to study its effect on mechanical properties of the composite. The effect of particulate surface modification using a silane coupling agent was also studied. Properties of the composites were characterized using standard testing methods. When compared to the largest particulate used, an increase in compression strength was achieved by particle size reduction and use of coupling agent. The Elastic modulus increased by using fine particles, while Poisson's ratio remained constant and independent of silane treatment or particle size. Fracture toughness increased with particle size reduction and increased further with silane surface modification. Dynamic compressive strength increased with particle size reduction, while silane did not show improvement. The addition of cenospheres as well as silane treatment increased the glass transition temperature for polyester. A given mass fraction of particulate, of a mean diameter D, will have the surface area between the particulate and matrix scale as D ^–1 (specific surface area). The sensitivity of these properties to cenosphere size is a direct function of the interfacial surface contacts between the polyester and the cenospheres and the specific surface area.     

Mixture law including particle-size effect on fracture toughness of nano- and micro-spherical particle-filled composites

The effects of particle diameter and volume fraction on fracture toughness of nano- and micro-spherical particle-filled composites were investigated. The purpose was to create a mixture law of fracture toughness based on experimental results of spherical silica particle–filled epoxy composites and a theoretical approach. The fracture toughness of composites was found to be tailored independently by exchanging different particle sizes, and elastic and viscoelastic properties were found to be governed by the volume fraction of the particles. In a theoretical analysis, a mixture law of fracture toughness, composed of the elastic moduli, diameter, and volume fraction of particles and the elastic moduli of matrix resins was proposed. Its validity was demonstrated in a comparison with the experimental results.     

Influence of boron carbide content on the microstructure,tensile strength and fracture behavior of boron carbide reinforced aluminum metal matrix composites

In the present work, an indigenously developed low cost modified stir casting technique is developed for the processing of 6061 Al‐B₄C composites containing high‐volume fraction of boron carbide particles (up to 20 vol. %). The influence of varying reinforcement content on the spatial distribution of boron carbide in the aluminum matrix is qualitatively characterized using scanning electron microscope. At a lower volume fraction of reinforcement, wide particle free zone and large interparticle spacing were observed in the matrix while the composite with high reinforcement content displayed relatively homogeneous and discrete particle distribution. X‐ray diffraction analysis confirms the presence of only aluminum and boron carbide diffraction peaks, indicating that no significant reaction occurs during composite processing. The tensile behavior of composites revealed that strength and ductility are influenced by varying particulate content. The quantitative analysis of strengthening mechanism in the casted composites showed that higher volume fraction of boron carbide lead to larger values of thermal dislocation strengthening, grain size and strain gradient strengthening. The morphology of fracture surfaces reveals the presence of dimple network and the average size of dimples gradually decreases with the increase in particulate content, which indicates the co‐existence of ductile and brittle fracture.     

Numerical analysis of the stress–strain distributions in the particle reinforced metal matrix composite SiC/6064Al

The axisymmetric cell model consisting of interface, matrix and reinforced particle is used to simulate the tensile test of particle reinforced metal matrix composite for predicting the micro stress/strain field and macro tensile stress/strain curve. In simulation of the tensile test, the cohesive element model is selected to model interfacial crack growth. It mainly analyzed the effects of interfacial properties, reinforcement volume fractions and aspect ratios on the stress–strain states of particle reinforced metal matrix composite. The results show that the peak micro stress and plastic strain occur at the interface in which it is a certain angle from the tensile stress direction; with the interfacial fracture toughness and reinforcement volume fraction increasing, the flow stress increases firstly and then decreases. The tensile stress–strain properties of SiC/6064Al are good when the interfacial fracture toughness is equal to 60 J/m and the reinforcement fraction volume is equal to 20%. Smaller reinforcement aspect ratio leads to smaller micro stress in composites.     

Fracture characteristics of Al/zircon particulate composites

A study has been made of the effects of volume fraction and size of zircon particulates on fracture toughness and micromechanisms of fracture in Al/zircon particulate composites. The composites are prepared by a liquid metallurgy technique using volume fractions of zircon in the range 0·06–0·18 and particulate sizes between 75 and 250 μm. The study was conducted on composites in the cast and the forged conditions. The experimental programme included a particle size distribution study, tensile tests, fracture mechanics tests leading to J_1c and crack tip opening displacement evaluation, fractographic investigations, etc. The process zone size at the crack tip was evaluated from crack tip stresses and strains, and compared with the interparticle spacing and particle diameter in order to understand the micromechanics of cracking. The Al/zircon composites were compared with Al/graphite composites in terms of strength and fracture toughness as a function of volume fraction of the filler phase, and regions of optimum performance were identified.     

Effects of SiCp size and volume fraction on the high cycle fatigue behavior of AZ91D magnesium alloy composites

High cycle fatigue tests (i.e., stress-controlled, axial) were conducted on monolithic AZ91D and AZ91D magnesinm alloy composites processed via squeeze casting and extrusion to contain either 15 gm or 52 gm size SiC particles, at both the 20% and 25% volume fraction reinforcement level. The effects of changes in SiC particle size and volume fraction on the high cycle fatigue behavior have been determined. In addition, the number of cracked particles on the fatigue fracture surfaces, as well as the level of damage beneath the fatigue fracture surfaces were quantified in order to determine the effects of particle size on the evolution of damage during fatigue and during overload failure. Commercial purity Mg specimens containing a large grain size were also tested in fatigue for comparison with the alloy and composite data.     

The effects of volume percent and aspect ratio of carbon fiber on fracture toughness of reinforced aluminum matrix composites

Carbon fiber reinforced aluminum matrix composites are used as advanced materials in aerospace and electronic industries. In order to investigate role of aspect ratio of carbon fiber on fracture toughness of aluminum matrix composite, the composite was produced using stir casting. Al–8.5%Si–5%Mg selected as a matrix. The samples were prepared with three volume fractions (1, 2 and 3) and three aspect ratios (300, 500 and 800). Three-point bending test was performed on the specimens to evaluate the fracture toughness of the materials. The results showed that the fracture toughness of composites depends on both fiber volume fraction and aspect ratio. Scanning electron microscopy (SEM) was employed to elucidate the fracture behavior and crack deflection of composites. The study also, showed that the toughening mechanism depends strongly on fiber volume fraction, aspect ratio and the degree of wetting between fiber and matrix.     

Mechanical reinforcement of unsaturated polyester by AL2O3 nanoparticles

Nanometer-sized Al₂O₃ particles (15 nm average diameter) were used as reinforcements to enhance the fracture toughness of a highly crosslinked, nominally brittle, thermosetting-unsaturated polyester resin. It was observed that the addition of untreated, as-received Al₂O₃ particles does not result in enhanced fracture toughness. Instead, the fracture toughness decreases by 15% as the volume fraction of the particles is increased from 0% to 4.5%. Similar degradation in fracture toughness was observed for reinforcement by 1- and 35-μm Al₂O₃ particles. The lack of reinforcement was attributed to poor particle-matrix bonding, as observed from scanning electron micrographs of the fracture surfaces. However, considerable reinforcement was observed when the nanocomposites were fabricated using an organofunctional silane to enhance particle-matrix interface strength. For the case of a 4.5% volume fraction of well-bonded Al₂O₃ particles added to the unsaturated polyester, the fracture toughness was increased by almost 100%.     

Epoxy composites with 200 nm thick alumina platelets as reinforcements

Composites were prepared by dispersing Alumina platelets of polygonal shape having a thickness of 200 nm and size of 5–10 μm in epoxy (LY 556) matrix using sonication. Good dispersion of the platelets was observed through scanning electron microscopy (SEM). The quasi-static plane-strain fracture toughness and tensile properties of the composites were determined for platelet volume fraction varying from 0% to 10%. The results indicated that addition of the platelets give considerable improvement in fracture toughness and good improvement in the elastic modulus of epoxy. For 10% volume fraction of the platelets, the fracture toughness improved by 110% where as the improvement in elastic modulus was 78%. However there was an associated reduction of 53% in tensile strength and 73% in failure strain. SEM of fractured surface was carried out to understand the various mechanisms responsible for the improvement in fracture toughness. By appropriately accounting for the orientation and stacking effects of the platelets, the applicability of predictive models, such as the Halpin-Tsai and Mori-Tanaka, for estimating the composite modulus is demonstrated.     

Studies on the fracture and flexural strength of Al/Sip composite

Pure aluminum matrix composite reinforced with a high volume fraction of silicon particles (Al/Si_p) was fabricated by gas-pressured infiltration. The results of four point flexural strength tests show that Al/Si_p has low flexural strength. The analysis of the fractograph reveals the fracture mechanism of Al/Si_p. The fracture of Al/Si_p is primarily dominated by the fracture of brittle silicon particles and the subsequent link up of damage through the matrix. The pre-existent microcracks in silicon particles that were made during the process of compacting will also lower the flexural strength of Al/Si_p composite. The hybrid particle reinforced pure aluminum matrix composite (Al/Si_p+SiC_p) was fabricated in the same way. Results show the flexural strength can be improved by 11.3% compared with Al/Si_p when 6 vol.% silicon particles are replaced by silicon carbide particles with the same volume fraction and size. The reason is that SiC_p with higher fracture stress and higher elastic modulus can prevent the rapid expansion of cracks through the composite and lower the stress in silicon particles.     

Influence of heat treatment and particle shape on mechanical properties of infiltrated Al2O3 particle reinforced Al-2 wt-%Cu

Abstract

Al-2 wt-%Cu composites were produced by gas pressure infiltration of powder beds with a high volume fraction (45 to 60 vol.-%) of angular or polygonal alumina particles. The tensile behaviour and fracture toughness of the composites were characterised in as cast, solutionised and peak aged (T6) conditions. It was shown that coarse intermetallics that are formed during solidification and located preferentially at the particle/matrix interface lead to lower toughness compared with the same composites in solutionised and T6 conditions. The particle nature and shape exert a strong influence on the properties of the composites: polygonal particles are intrinsically stronger than angular particles and yield stronger, tougher, and more ductile composites. Composite toughness variations are explained in terms of fracture micromechanisms.     

新型颗粒增强金属玻璃复合材料的拉伸增韧机制

利用有限元方法探究了颗粒体积分数、颗粒的应变硬化指数、颗粒的间距以及网状结构对新型非晶合金复合材料即金属玻璃基复合材料（Metallic Glass Composites,MGCs）强度和韧性的影响。结果表明：随着颗粒应变硬化指数的增大,复合材料的强度和韧性都有很大提高,颗粒体积分数的增大、颗粒间距的变小和网状结构排布也将提高复合材料的韧性。这些都有利于设计出有较好韧性的复合材料。     

The influence of particle size on the tensile strength of particulate — filled polymers

The tensile strengths of a particulate-filled rigid polyurethane resin are presented at varying volume fractions and a wide range of particle sizes. These results are compared with exisiting theories of the strength of particulate-filled composite systems. A linear relationship is proposed to exist between the mean particle diameter and the tensile strength at a given volume fraction. A method of normalizing data is presented which removes the stress-concentration effects of finite particle sizes and allows comparison of the data with a simple equation relating tensile strength and volume fraction. The effects of particle size and volume fraction in relation to crack propagation are discussed, and the proposed method of analysis is shown to give similar results when applied to published data.     

Fracture toughness behaviour of a magnesium alloy metal-matrix composite produced by the infiltration technique

Metal-matrix composites comprising short δ-alumina fibres embedded in an Mg 10Al0.4Zn alloy were produced by the squeeze infiltration process, with a fibre volume fraction of 20%. Tensile, hardness and fracture toughness tests were performed at room temperature on both the alloy matrix and the composite in the as-cast as well as in the T6 heat-treated condition. In the as-cast condition it was found that the composite had a markedly increased stiffness, tensile strength and hardness but slightly lower ductility and fracture toughness than the alloy matrix. Whilst a T6 heat treatment improved the mechanical properties of the magnesium alloy matrix, it adversely affected the tensile properties and fracture toughness of the composite.     

Fracture of alumina particulate reinforced aluminium alloy matrix composites

Fracture toughness tests were performed on two aluminium alloy matrices, 2014-0 and 2024-0 reinforced with alumina particulates of different volume fractions and particulate sizes so as to investigate the fracture mechanisms operative in such composites and to determine how microstructural parameters such as volume fraction, particulate size and interparticle spacing affect the fracture toughness. The results indicate that fracture occurred by a locally ductile mechanism. The fracture toughness increased with increasing particle spacing provided that the particle size was less than a limiting value, above which unstable crack growth occurred and the toughness lowered.     

Statistical analysis of the fracture strengths of aluminum alloy–alumina (Al<Subscript>2</Subscript>O<Subscript>3</Subscript>) particulate composites

The mechanics of composite materials and their “fracture behaviors” are relatively complex phenomena to analyze and establish due to their inconsistent process stability and reliability, combined with production and related processing problems. In this work, an attempt has been made to statistically analyze the tensile behavior of metal matrix composites. Composites of aluminum alloy containing 5–20% volume fraction of Al₂O₃ particles of 15 μm size were prepared by adding alumina particles to a vigorously agitated semi-solid aluminum alloy. Prior to this, alumina particles were subjected to preheating at 800 °C for 5 h. Particles were then added to the aluminum alloy and further heated to 850 °C by using a mixer in a nitrogen medium. A total of 20 tension tests were performed for each volume fraction according to ASTM Standards B557 and using these test data, the initial estimators for an empirical model were obtained. Using this empirical model, the reliability of the composite characteristics in terms of its tensile strength was assessed. Another significant implication of the present study is proving the ability and utility of the Weibull statistical distribution for describing the experimentally measured data on the tensile strength of metal matrix composites, in a more appropriate manner.     

A theoretical approach for the thermal expansion behavior of the particulate reinforced aluminum matrix composite Part I A thermal expansion model for composites with mono-dispersed spherical particles

Microstructural observation revealed that the increase in the volume fraction of SiC particles lowers the coefficient of thermal expansion (CTE) of the composite, and the CTE of the metal matrix composites is proportional to the size of the Si phase. To analyze the thermal expansion behavior of aluminum matrix composites, a new model for the CTE of the mono-dispersed binary composite on the basis of Ashelby's cutting and welding approach was proposed. In the theoretical model, it was considered that during cooling relaxation of residual stresses could create an elasto-plastic deformation zone around a SiC or Al₂O₃ particle in the matrix. The size of reinforced particles and other metallurgical factors of the matrix alloy and composite were also considered. In this model, the interacting effect between the reinforced hard particle and the soft matrix is considered by introducing the influence of the elasto-plastic deformation zone around a particle, which is distinguished from the previous models. It was revealed that the CTE of the composite are influenced by the particle volume fraction, the elastic modulus and Poisson's ratio as well as the elasto-plastic deformation zone size and the particle size.     

On the Applicability of the Schwalbe's Model to the Fracture Toughness Calculation in 7075 Aluminum Alloys

Four 7075-T651 aluminum alloys have been tested in tension in order to assess the applicability of the Schwalbe's model to the fracture toughness calculation. Standard K _IC tests were performed on compact tension samples at room temperature, and the results compared with those from the Schwalbe's model which takes into account several mechanical properties derived from a conventional tensile test applied on round unnotched tensile samples, and the average dimple size of the corresponding fracture surfaces. The values of K _IC calculated through the Schwalbe's model, correlate qualitatively well with those from the standard technique.Fracture toughness deterioration is accompanied by a loss of the true fracture strain, strain hardening capacity and average dimple size. On the other hand, the higher the Zn/Mg ratio, the volume fraction of precipitates and the yield strength, the lower the fracture toughness. All these effects are originated in the presence of matrix precipitates. Therefore, the reduction in K _IC can be explained in terms of the matrix response to the applied stress field as a function of the differences in volume fraction of the strengthening precipitates.The round tension samples corresponding to the four materials, failed in a predominantly ductile transgranular fashion, which facilitates the application of the Schwalbe's model based in the characteristic dimples, developed in this mode of fracture, as a microstructural element size.