Effects of random particle dispersion and size on the indentation behavior of SiC particle reinforced metal matrix composites

This study investigates the effects of particle size, volume fraction, random dispersion and local concentration underneath a spherical indenter on the indentation response of particle reinforced metal matrix Al 1080/SiC composites. The ceramic particles in certain sizes and volume fractions were randomly distributed through the composite structure in order to achieve a similar structure to an actual microstructure as possible. The particle size and volume fraction affected considerably indentation depths and deformed indentation surface profiles. The indentation depth increases with increasing particle size, but decreases with increasing particle volume fraction. The experimental indentation depths were in agreement with numerical indentation depths in case the local particle concentration effect is considered. The local particle concentration plays an important role on the peak indentation depth. For small particle sizes and large volume fractions the random particle distribution affects the deformed surface profiles as well as the indentation depths. However, its effect is minor on residual stress and strain distributions rather than levels in the indentation region.     

Failures analysis of particle reinforced metal matrix composites by microstructure based models

This paper discusses the methodology of microstructure based elastic–plastic finite element analysis of particle reinforced metal matrix composites. This model is used to predict the failure of two dimensional microstructure models under tensile loading conditions. A literature survey indicates that the major failure mechanism of particle reinforced metal matrix composites such as particle fracture, interfaces decohesion and matrix yielding is mainly dominated by the distribution of particles in the matrix. Hence, analyses were carried out on the microstructure of random and clustered particles to determine its effect on strength and failure mechanisms. The finite element analysis models were generated in ANSYS, using scanning electron microscope images. The percentage of major failures and stress–strain responses were predicted numerically for each microstructure. It is evident from the analysis that the clustering nature of particles in the matrix dominates the failure modes of particle reinforced metal matrix composites.     

Simulation of damage evolution in discontinously reinforced metal matrix composites: a phase-field model

In this study, a phase-field model is introduced to model the damage evolution, due to particle cracking in reinforced composites in which matrix deformation is described by an elastic-plastic constitutive law exhibiting linear hardening behavior. In order to establish the viability of the algorithm, the simulations are carried out for crack extension from a square hole in isotropic elastic solid under the complex loading path, and composites having the same volume fraction of reinforcements with two different particle sizes. The observed cracking patterns and development of the stress-strain curves agree with the experimental observations and previous numerical studies. The algorithm offers significant advantages to describe the microstructure and topological changes associated with the damage evolution in comparison to conventional simulation algorithms, due to the absence of formal meshing.     

Development of a finite element micromodel for metal matrix composites

A finite element micromodel has been developed based on real microstructures. The method of modelling is unique in that displacements calculated from large-specimen models are used as boundary conditions to model more accurately at the microstructural level. The development was centred around determining the response of the matrix, near a crack tip, to the constraint imposed by the particles. The process of developing the model is given and the final result is compared with experimentally measured values of constraint from the stereoimaging analysis of the photographs the model was based on. Good agreement was found and both techniques, stereoimaging and FEM, verified each other.     

Phase-stress partition and residual stress in metal matrix composites

Finite element (FE) modeling based on axisymmetrical cells was performed for relating the phase-stress partition and residual phase stress in metal matrix composites (MMCs) to the reinforcement volume fraction and shape, matrix hardening behavior and applied strain levels. The phase stress is defined as mean effective stresses in the constituent phases. The elastic, plastic phase-stress partition behavior during loading, and the resultant residual stress in matrix followed unloading are delineated. A set of formulas is given for predicting the value of the phase stress in each phase, and residual stress in matrix from the inclusion volume fraction and aspect ratio, as well as matrix hardening exponent and applied strain level.     

Characterization of particle concentration in indentation-deformed metal-ceramic composites

Previous studies have shown that the indentation technique is prone to overestimate the overall strength of heterogeneous materials containing hard particles in a ductile matrix. The localized increase in particle concentration under the indentation has been proposed as a possible cause. In this study, a direct characterization is undertaken using an aluminum/silicon carbide metal matrix composite. Quantitative metallography on the post-indented material is carried out to measure the particle volume fraction. A distinct increase in particle concentration induced by the indentation is found. The spatial distribution of particle concentration is also examined in detail. The residual compressive stress field remained in the material after unloading, as illustrated by the finite element analysis, is shown to correlate with the experimental measurement of the particle concentration.     

Constituent damage mechanisms in metal matrix composites under fatigue loading, and their effects on fatigue life

Load controlled fatigue experiments were performed on 8-ply unidirectional ([0]₈) SCS-6-Ti-15-3 metal matrix composites (MMCs) at different temperatures, and the results were interpreted in terms of the overall three-regime framework of fatigue. The emphasis was on understanding the mechanisms and mechanics of constituent damage evolution, and their effects on fatigue life. Most tests were performed at an R-ratio of 0.1, but limited fully-reversed (R = −1) tests were conducted. In regime 1, damage was fiber failure dominated, but the exact mechanisms were different at room and elevated temperatures. In regime 2, observation of matrix cracks and persistent slip bands provided convincing evidence of matrix dominated damage. Weak fiber-matrix interfaces contributed to crack bridging. However, fiber fracture also played an important role in regime 2; tension-tension and tension-compression tests showed similar lives on a maximum fiber stress basis, although the strain range, which primarily controls matrix crack growth, was almost double for R = −1 compared with R = 0 or 0.1. Good agreement was obtained from the different R-ratio tests, between the MMC and matrix data, and data at room and elevated temperatures, when compared based on the strain range in the tension part of a cycle. Analyses and observations of fiber pull-out lengths and fiber fractures in the matrix crack wake provided evidence of fiber damage; the analyses also helped to explain increased fiber bridging with fiber volume fraction. Issues of fatigue life prediction are briefly discussed.     

Interface damage of SiC/Ti metal matrix composites subjected to combined thermal and axial shear loading

A three-dimensional micromechanical finite element model is developed to study initiation and propagation of interface damage of unidirectional SiC/Ti metal matrix composites (MMCs) subjected to combined thermal and axial shear loading. Effects of various important parameters such as manufacturing process thermal residual stress, fiber coating and interface bonding are investigated. The model includes a representative volume element consists of a quarter of SiC (SCS-6) fibers covered by interface and coating, which are all surrounded by Ti-15-3 matrix. Appropriate boundary conditions are introduced to include effects of combined thermal and axial shear loading on the RVE. A suitable failure criterion for interface damage is introduced to predict initiation and propagation of interface de-bonding during shear loading. It is shown that while predictions based on perfectly bonded and fully de-bonded interface are far from reality, the predicted stress–strain curve for damaged interface demonstrates very good agreement with experimental data.     

In situ fibre strength determination in metal matrix composites

Single fibre fragmentation tests were performed at room temperature on SiC/Ti-6242 specimens in order to estimate the in situ fibre strength. Tensile specimens were instrumented with two acoustic emission transducers and an extensometer in order to monitor the strain at which fibre breaks occurred. Data analysis utilized Monte Carlo simulations of fibre fragmentation. The fibre/matrix stress transfer profile near a fibre break was derived using a finite element analysis. Cohesive zone model is used to describe damage of the interfacial zone. Thermally induced residual stresses and matrix plastic deformations were accounted for. The results presented in this paper show that the in situ Weibull parameters of the fibre are smaller than the reference obtained on as received fibres. Analysis of data raised questions about the validity of the Monte Carlo simulation method.     

Ultrasonic evaluation of fatigue damage in metal matrix composites

This paper describes an experimental nondestructive technique for fatigue damage assessment in metal matrix composites by measuring ultrasonic phase velocity and attenuation. A [0/90] SiC/Ti---15V---3Cr---3Al---3Sn metal matrix composite is considered as a model system. Cyclic loading at 50 and 70% of the ultimate sample strength were used until failure. The ultrasonic phase velocities and attenuations were measured periodically and found to be very sensitive to fatigue damage. The fatigue-induced changes in the composite elastic constants were calculated from the measured ultrasonic velocity data. For samples heat treated prior to fatigue (815°C) above the matrix β transus (about 760°C), the dominant damage mechanism is debonding of the fiber/matrix interface. We found that when samples were fatigued for less than 50% of the lifetime, the reduction of the composite moduli was linearly dependent on the number of fatigue cycles, which is explained by extension of interfacial partial debonds. This was supported by micromechanical analysis based on a partial disbond model. The rate of decrease in the composite moduli in the second half of the fatigue life was found to be lower, which may serve as a basis for estimation of the remaining fatigue life of the composite from ultrasonic velocity and attenuation measurements. The attenuation data was obtained in directions perpendicular to the fiber. A single-fiber scattering model has been used to explain the effect of the fiber/matrix interface on attenuation. Good correlation between attenuation and moduli measurements was observed.     

Fatigue properties of friction stir welded particulate reinforced aluminium matrix composites

Few papers have discussed the friction stir welding (FSW) of particulate reinforced aluminium matrix composites and most of them focused on the set-up of the welding process parameters and their effect on microstructure, hardness and tensile behaviour. The aim of this study was to investigate the fatigue resistance of FSW joints on an as-cast particulate reinforced aluminium based composite (AA6061/22 vol.%/Al₂O_3p). The welding process was performed using different process parameters, also investigating their effect on joint microstructure. The mechanical properties of the FSW composites were compared with those of the base material and the results were correlated to the microstructural modifications induced by the FSW process on the aluminium alloy matrix and the ceramic reinforcement. FSW reduced the size of both particle reinforcement and aluminium grains, and also led to a significant increase in interparticle matrix microhardness, for all process parameters. The FSW specimens belonging to a different set of parameters, tested without any post-weld heat treatment, exhibited a very high joint efficiency (ranging from 90% to 99%) with respect to the ultimate tensile strength of the base material. The stress controlled fatigue test showed a high spread both for the base and FSW composites. Statistical analysis disclosed that all FSW specimens belonging to different process parameters showed apparently slightly worse fatigue behaviour than that of the base composite. Statistical processing applied to the different welding parameters revealed that all the welded specimens belonged to the same population. Therefore it can be concluded that the parameters used produced joints with similar microstructure and comparable fatigue behaviour. The slight difference in the fatigue behaviour of the FSW specimens whose process parameters differed form those of the unwelded composite was explained by the different microstructural homogeneity in the transition from the base to the FSW zone.     

Stress enhancement at inclusion particles in aluminum matrix composites: computational modeling and implications to fatigue damage

The evolution of stresses inside the native inclusion particles in silicon carbide (SiC) particulate reinforced aluminum (Al) matrix composites is studied computationally by recourse to the finite element method. It is motivated by the experimental findings that inclusion fracture serves as the fatigue crack initiation in such types of composite materials. The analyses were performed for a simplistic model, with the inclusion embedded within a homogeneous material bearing the properties of Al/SiC mixture, and a refined model, with the inclusion, Al matrix and SiC particles specifically included. The simplistic model was found to be able to predict the stress enhancement in the inclusion that is consistent with the measured propensity of fatigue crack initiation when elasticity dominates. When plastic yielding occurs, the simplistic model failed to predict the experimental trend due to its inability to capture the highly non-uniform plastic flow field within the Al matrix. The refined three-phase model is needed for the plastic analysis. Implications of the present findings to general numerical modeling of composite materials are discussed.     

碳化硅增强铝基复合材料的力学性能和断裂机制

研究了碳化硅颗粒(SiCp)尺寸对用粉末冶金法制备体积分数为15%的SiCp/2009铝基复合材料力学性能和断裂机制的影响.结果表明,复合材料的强度随着SiCp尺寸的增大而减小,塑性则随着颗粒的增大而增大.当SiCp尺寸为1.5μm时,SiCp/2009A1复合材料的断裂主要以界面处撕裂和基体材料的开裂为主;当SiCp尺寸为20 μm时,复合材料的断裂主要以SiCp断裂为主;当SiCp尺寸处于两者之间时,SiCp/2009A1复合材料界面处撕裂和SiCp断裂的共同作用决定复合材料的断裂.     

含脆性界面相的颗粒增强金属基复合材料的损伤

通过引入双夹杂模型,将传统增量损伤理论扩展应用到三相复合材料颗粒尺寸效应问题,同时提出一个可以研究颗粒增强金属基复合材料的弹塑性变形及渐进式脱黏损伤模型,该模型还可以研究含脆性界面相的颗粒增强金属基复合材料弹塑性损伤变形行为的颗粒尺寸效应。研究发现,包含各种不同颗粒尺寸的颗粒增强金属基复合材料的脱黏损伤按照颗粒尺寸从大到小的顺序先后发生,并且该模型与SiC/Al复合材料的试验结果比较一致。     

颗粒增强金属基复合材料涂层的制备及其特性与应用

针对复合材料涂层的相关问题, 综述了颗粒增强金属基复合材料涂层的制备技术及其特性的研究进展。重点描述了电热爆炸超高速喷涂技术及电刷镀技术制备颗粒增强金属基复合材料涂层的发展现状、涂层组织结构和力学性能研究进展, 概述了颗粒增强金属基复合材料涂层的工程应用领域及其未来发展方向。     

Investigation on diffusion bonding characteristics of SiC particulate reinforced aluminium metal matrix composites (Al/SiCp-MMC)

Joining characteristics of SiC particulate reinforced aluminium metal matrix composites (Al/SiC_p-MMC) were investigated by vacuum diffusion bonding process. The joining performances of the similar and dissimilar composites were studied, and the influences of SiC_p volume percentage and the insert alloy layer on bonding quality and properties of the bonded joints were also estimated. The experimental results indicate that the strength of vacuum diffusion bonded joints decreases with increasing SiC_p volume percentage, and obtaining satisfactory bonding quality in the diffusion bonded joints of the dissimilar Al/SiC_p-MMC is much more difficult than that of the similar Al/SiC_p-MMC. Moreover, the results still manifest that the diffusion bonding either for the similar or for the dissimilar Al/SiC_p-MMC, the suitable insert alloy layer can improve evidently the joining quality of joints, and the strength of diffusion bonded joints corresponding to using the insert alloy layer is apparently higher than that of no insert layer.     

Experimental investigation and FE simulation of spherical indentation on nano-alumina reinforced copper-matrix composite produced by three different techniques

Preparation of metal matrix composites with homogenously distributed reinforcement is a difficult process. The process can be even more complex when the reinforcement particles are nano-particles. In this paper, three different techniques (dry mixing, mechanical alloying and mechanochemical) were applied to produce Cu-Al₂O₃ nano composite with three different Al₂O₃ content (2.5, 7.5 and 12.5 .wt.%). XRD, SEM and EDX analysis were conducted to analyse the physical and structural properties of the produced samples. Rockwell hardness test and compression test were applied to determine the mechanical properties of the produced composites. A 2D axisymmetric FE model was implemented using commercial software to predict the Rockwell hardness of the prepared samples. The results show that dry mixing and mechanical alloying techniques are valid for production of metal matrix composites with large reinforcement particle size and low reinforcement content. However, mechanochemical technique can be used to produce Cu-Al₂O₃ nano composite with high reinforcement weight fractions. Homogenously distributed dispersed nano alumina copper matrix can be achieved by applying mechanochemical technique and as a result, the mechanical and physical properties can be improved. The hardness predicted by the presented FE model correlates well with the experimental observation.     

Size dependent strengthening mechanisms in carbon nanotube reinforced metal matrix composites

The matrix grain size plays a dual role in metal matrix composites (MMCs). Contrary to enhance the strength of matrix, grain refinement can weaken the thermal expansion mismatch strengthening induced by the reinforcement. In this article, a dislocation density based model is developed to describe the factors affecting the strengthening mechanisms in Carbon nanotube (CNT)-reinforced MMCs with different matrix grain sizes. Two kinds of thermal expansion mismatch strengthening mechanisms are considered, i.e., geometrically necessary dislocations (GNDs) are distributed in entire matrix and GNDs are limited in dislocation punched zones (DPZs). In addition, comparisons between the predictions and some available experimental results are also performed.     

颗粒增强镁基复合材料的研究现状及发展趋势

综述了颗粒增强镁基复合材料的研究概况,着重介绍了颗粒增强镁基复合材料的制备技术,界面行为和制备热力学与动力学三大研究热点,另外,对颗粒增强镁基复合材料的增强机理及常温力学性能作了简单介绍,最后,对颗粒增强镁基复合材料的研究方向进行了一些看法和展望,指出原位颗粒增强镁基复合材料的制备技术交城为制备镁基复合材料的发展趋势,镁基复合材料由于具有高的比强度,比模量和良好的耐磨性、耐高温性能和减震性能,在航空航天,特别是汽车工业具有在的应用前景和广阔的市场。     

石墨烯增强金属基航空复合材料研究进展

本文综述了石墨烯增强金属基航空复合材料的研究现状,归纳了该种复合材料的制备方法,讨论了石墨烯对其性能的影响及机制。指出目前高含量、排列石墨烯增强金属基航空复合材料的研究还比较缺乏,涉及的工艺参数、组织结构、界面化学及高温物理性能等相关问题仍需进一步研究,并提出未来的研究重点应由制备方法等工艺性探讨向微观复合构型设计的思路转变。