An FEM investigation into the behavior of metal matrix composites: Tool–particle interaction during orthogonal cutting

An analytical or experimental method is often unable to explore the behavior of a metal matrix composite (MMC) during machining due to the complex deformation and interactions among particles, tool and matrix. This paper investigates the matrix deformation and tool–particle interactions during machining using the finite element method. Based on the geometrical orientations, the interaction between tool and particle reinforcements was categorized into three scenarios: particles along, above and below the cutting path. The development of stress and strain fields in the MMC was analyzed and physical phenomena such as tool wear, particle debonding, displacements and inhomogeneous deformation of matrix material were explored. It was found that tool–particle interaction and stress/strain distributions in the particles/matrix are responsible for particle debonding, surface damage and tool wear during machining of MMC.     

颗粒团聚对Al基SiC颗粒增强复合材料的流变形为影响

基于微观组织的有限元分析模型,研究颗粒团聚对Al基SiC颗粒增强金属基复合材料流变行为的影响。通过建立的3种增强颗粒分布的胞元模型（一个团聚现象、两个团聚现象和随机分布）,分析讨论基体和增强颗粒中的等效应力和等效应变的分布规律,以此为基础,获得3种颗粒分布模型下的SiC颗粒增强Al基复合材料的应力应变曲线。结果表明：颗粒增强金属基复合材料的流变行为和力学响应与增强颗粒的分布非常敏感,但在弹性变形阶段这种影响就相对较弱。从增强颗粒的最大主应力分布来看,颗粒团聚增加了SiC颗粒开裂的概率。从基体的静水应力分布来看,颗粒团聚将促进早期的界面脱粘和在韧性基体中形成微空洞。     

Effect of particle cracking on the strength and ductility of Al-SiCp powder metallurgy metal matrix composites

The effects of particle cracking on the strength and ductility of Al-SiCp metal matrix composite material (MMC) was investigated. The composite was manufactured using a simple powder metallurgy (PM) technique of hot pressing followed by hot extrusion. Also, the effects of reinforcement weight fraction and strain rate variations on the strength and ductility of the same composite were examined. It was found that particle cracking plays a significant role in controlling the mechanical properties of the composite. It was shown that particle cracking is possible in an MMC material made with a low strength matrix (commercially pure aluminum), and increases with the increase of reinforcement weight fraction, applied strain rate, and amount of plastic deformation. The yield strength increases as a function of reinforcement weight fraction and to a lesser extent as the strain rate increases. The tensile strength increases at low SiCp weight fractions, then remains constant or decreases as more particles are added to the matrix.     

颗粒形状对铜合金薄带表层断裂影响的数值分析

根据引线框架Cu—Fe-P合金精轧后表层断裂处形状各异Fe颗粒的组织几何形态，建立有限元数值分析模型，主要研究了不同Fe颗粒形状下残余应力对基体与界面处应力集中现象的影响。数值分析表明，随着颗粒尖角程度的增加，Fe颗粒和Cu基体界面处存在剧烈的应力集中和较大的残余应力，从而导致铜合金薄带表层断裂。因此在引线框架铜合金的生产过程中，应避免较大的尖角Fe颗粒存在。     

Effects of particle arrangement and particle damage on the mechanical response of metal matrix nanocomposites: A numerical analysis

The spatial distribution of reinforcement particles has a significant effect on the mechanical response and damage evolution of metal matrix composites (MMCs). It is observed that particle clustering leads to higher flow stress, earlier particle damage, as well as lower overall failure strain. In recent years, experimental studies have shown that reducing the size of particles to the nanoscale dramatically increases the mechanical strength of MMCs even at low particle volume fractions. However, the effects of particle distribution and particle damage on the mechanical response of these metal matrix nanocomposites, which may be different from that observed in normal MMCs, has not been widely explored. In this paper, these effects are investigated numerically using plane strain discrete dislocation simulations. The results show that non-clustered random and highly clustered particle arrangements result in the highest and lowest flow stress, respectively. The effect of particle fracture on the overall response of the nanocomposite is also more significant for non-clustered random and mildly clustered particle arrangements, in which particle damage begins earlier and the fraction of damaged particles is higher, compared to regular rectangular and highly clustered arrangements.     

SiC颗粒增强铝基复合材料的热循环行为研究

基于材料微观组织建立了视场胞元模型,并采用商用有限元软件ABAQUS对胞元模型进行温度循环的数值模拟,着重分析热循环中基体和增强颗粒的等效应力分布规律,及主应力σ_(11)和σ_(22)的分布规律.结果表明:在热循环的升温阶段,基体的主热应力整体表现为压应力,增强颗粒表现为拉应力;在降温阶段,基体表现为拉应力,增强颗粒表现为压应力;在模拟中,对3次循环中的主热应力σ_(22)做了统计,发现不论是基体还是增强颗粒,从第2次循环开始,热应力就开始趋于稳定.通过改变单元胞中颗粒的体积分数进一步分析体积分数变化对颗粒增强金属基复合材料热循环的影响,结果发现体积分数减小之后,基体和增强颗粒应力分布变得均匀,并且各次循环中的热应力相差不大,比较稳定.最后对热循环中的应变滞后回线进行了分析,表明高体积分数下的复合材料具有高的热稳定性.     

Finite Element Analysis of the Microstructure–Strength Relationships of Metal Matrix Composites

The influence of the shape and spatial distribution of reinforced particles on strength and damage of metal matrix composite （MMC） is investigated through finite element method under uniaxial tensile, simple shear, biaxial tensile, as well as combined tensile/shear loadings. The particle shapes change randomly from circular to regular n-sided polygon （3 ≤ n ≤ 10）; the particle alignments are determined through a sequentially random number stream and the particle locations are defined through the random sequential adsorption algorithm. The ductile failure in metal matrix and brittle failure in particles are described through damage models based on the stress triaxial indicator and maximum principal stress criterion, respectively, while the debonding behavior of interface between particles and matrix is simulated through cohesive elements. The simulation results show that, under different loadings, interface debonding is the dominated failure mechanism in MMCs and plastic deformation and ductile failure of matrix also play very important roles on the failure of MMCs.     

Microstructure-based modeling of the influence of particle spatial distribution and fracture on crack growth in particle-reinforced composites

The crack growth behavior of particle-reinforced composites is determined by several factors, such as volume fraction, particle size, particle morphology, spatial distribution and particle strength. Thus, an accurate and robust numerical model must incorporate the true microstructure of the particles. It will be shown that the strength of the reinforcement particles is also an important factor. Hence, the model must be able to simulate particle fracture. In this paper, the crack growth behavior of SiC particle-reinforced Al matrix composites was modeled using actual microstructures. Linear elastic fracture mechanics principles were used to propagate the crack and obtain the local stress intensity values. The effect of particle fracture on crack growth was studied. It will be shown that spatial distribution and shape of the particles, as well as particle fracture ahead of the crack tip, significantly affect the crack trajectory and the stress distribution at the crack tip.     

The influence of the reinforcing particle shape and interface strength on the fracture behavior of a metal matrix composite

A numerical analysis of the reinforcing particle shape and interface strength effects on the deformation and fracture behavior of an Al/Al₂O₃ composite is performed. Three-dimensional calculations are carried out for five elastic–brittle particles embedded into the elastic–plastic matrix, the reinforcing particle shape being varied from spherical to strongly irregular. It is shown that microstructural heterogeneity of the composite gives rise to a complex stress–strain state in the vicinity of particle boundaries and hence to near-interface areas undergoing tensile deformation both in tension and compression. Within the strain range under study, compressive strength is not achieved, either in compression or in tension, i.e., all cracks grow only under tensile stress. Particle fracture is found to occur by two mechanisms: interface debonding and particle cracking. Individual and combined effects of the particle shape, interface strength, and loading conditions on the fracture mechanisms are analyzed.     

Fatigue crack growth resistance of SiC<Subscript>p</Subscript> reinforced Al alloys: Effects of particle size,particle volume fraction,and matrix strength

The main aim of this work was to study the effects of particle size, particle volume fraction, and matrix strength on the long fatigue crack growth resistance of two different grades of Al alloys (Al2124-T1 and Al6061-T1) reinforced with SiC particles. Basically, it was found that an increase in particle volume fraction and particle size increases the fatigue crack growth resistance at near threshold and Paris regimen, with matrix strength having a smaller effect. Near final failure, the stronger and more brittle composites are affected more by static modes of failure as the applied maximum stress intensity factor (K _max) approaches mode I plane strain fracture toughness (K _IC).     

等温锻造对碳化硅颗粒增强铝基复合材料断裂韧性的影响

开展了粉末冶金法制备的20%SiC_p/2009Al复合材料坯锭的等温锻造实验,通过金相观察、扫描电镜(SEM)、拉伸和断裂韧性测试等方法研究了不同变形量对锻件微观组织和力学性能的影响。结果表明,随着等温锻造变形量的增大,SiC颗粒分布更加均匀,锻件的强度和塑性显著提高。通过SEM对材料断裂韧性裂纹扩展路径观察发现,主裂纹扩展发生在SiC颗粒偏聚区域的铝基体中。复合材料的断裂方式为以基体韧性断裂和增强体脆性断裂这2种方式为主。     

Distribution of stress and strain between adjacent particles in particulate reinforced metal matrix composites

The distribution of stress and strain between adjacent particles in particulate reinforced metal matrix composites was investigated using cohesive zone models. It is found that the strain of the composite is concentrated in the matrix, and there is a region with higher strain along the loading path, which can promote the formation of a void near the particles pole. The stress and strain in matrix near the particles gradually decrease with the increase of the distance between particles. And it is calculated that there is a critical distance within which the stress and strain fields of the neighboring particles can influence with each other. This critical distance increases with the increase of particle size. It is also found that the angle between the tensile direction and the center line of particles plays an important role in the stress and strain distribution. The model with the angle of 0° has the greatest influence on the distribution of stress and strain in the matrix, while the model with the angle of 45° has the least influence on the distribution of stress and strain in the matrix.     

Influence of powder particle injection velocity on the microstructure of Al-12Si/SiCp coatings produced by laser cladding

The influence of powder particle injection velocity on the microstructure of coatings consisting of an Al-Si matrix reinforced with SiC particles prepared by laser cladding from mixtures of powders of Al-12 wt.% Si alloy and SiC was investigated both experimentally and by modeling. At low injection velocities SiC particles react with the molten aluminum alloy. Only a small fraction of SiC remains in the microstructure, which contains large amounts of particles of the reaction products Al₄SiC₄ and Si dispersed in the α-Al + Si eutectic matrix. By contrast, at high injection velocities chemical reactions between SiC and molten aluminum are almost entirely suppressed and the resulting microstructure consists only of SiC particles dispersed in the matrix. To investigate whether this behavior could be explained by the different temperatures reached by the injected particles as they fly through the laser beam, a physical-mathematical model describing the interaction between the laser beam and the powder stream in the off-axis blown powder laser cladding process was developed and applied to calculate the temperature attained by the powder particles as a result of their interaction with an Nd:YAG laser beam (λ = 1.06 µm). At an injection velocity of 1 m/s the maximum temperature attained by SiC and Al-12Si particles is 3150 and 180 ºC, respectively. This result demonstrates that particle injection velocity is a major parameter affecting the microstructure of coatings produced by laser cladding, and must be carefully controlled.     

6061铝合金均匀化过程中AlMnSi弥散颗粒的析出尺寸对再结晶行为的影响

利用力学性能测试、光学显微镜、扫描电镜、透射电镜和能谱分析技术等手段研究了均匀化过程中AlMnSi弥散颗粒的析出尺寸对6061铝合金再结晶行为的影响。结果表明:AlMnSi弥散颗粒在均匀化过程中沿着铝基体[001]晶带轴析出长大,晶体结构为体心立方结构。随着均匀化温度的升高,弥散颗粒的析出尺寸逐渐增大,当AlMnSi弥散颗粒平均尺寸由0.07 μm增长到0.42 μm,最大尺寸由0.21 μm增大到1.12 μm时,力学性能则是先升高后降低。6061铝合金T6态组织仍为变形组织;AlMnSi弥散颗粒尺寸增大到1.12 μm,6061合金T6态组织中出现粗大再结晶,力学性能急剧降低。     

TiB2陶瓷颗粒增强的金属基复合涂层

采用电弧喷涂制备TiB2陶瓷颗粒增强的NiCr-TiB2,NiCr-TiB2/Al2O3和304L-TiB2及304L-TiB2/Al2O3四种金属基复合涂层.采用光学显微镜、扫描电子显微镜(SEM)结合透射电子显微镜(TEM)观察和详细分析了TiB2陶瓷颗粒增强复合涂层的显微组织及微观结构,探讨涂层的形成机理.结果表...     

Micromechanics constitutive model for predicting the stress–strain relations of particle toughened bulk metallic glass matrix composites

Based on the secant modulus and extended Mori-Tanaka method for dual ductile phases, a micromechanics model is proposed to predict the monotonic mechanical behaviors of bulk metallic glass matrix composites (BMGCs) toughened by particles. In this model, the deformation behaviors of the BMG matrix and particles are described by the use of the free volume model and the simple Ludwik flow equation, respectively, and Weng's homogenization frame is adopted to bridge the constituents and the composites. As compared to the existing relevant models, the present model is much more convenient for applying, and more readily to be extended. The developed model is applied with stain-controlled loading, and is verified by modeling the monotonic stress–strain relations of particle toughened BMGCs. The predictions were in good agreement with the experiments from the literature, which confirms that the developed analytical model is capable of successfully describing the mechanical properties, such as yield strength, stress hardening and strain softening elongation, of composites.     

含夹杂TiC-TiB_2陶瓷强度的细观力学分析

根据超重力合成TiC-TiB_2装甲陶瓷的细观结构和断裂机理,建立TiC-TiB_2装甲陶瓷细观强度模型,分2种失效形式讨论了氧化铝杂质颗粒对材料强度的影响。首先根据相互作用直推估计法计算了TiC-TiB_2基体的等效刚度,认为氧化铝杂质颗粒稀疏分布在TiC-TiB_2形成的等效基体中,根据等效夹杂理论计算了杂质颗粒内部和附近残余应力和应力场分布,得出氧化铝杂质颗粒可能的失效形式;然后根据杂质颗粒可能出现的界面脱粘和颗粒破坏2种失效形式分别建立模型进行讨论,并以两者的最小值定义为复合材料的强度,分析了材料强度随细观结构和性能参数的变化规律,并与实验结果进行了对比。结果表明,模型能够反映材料失效机理,对于具有与本文相似细观结构的材料,杂质颗粒与等效基体的相对弹性性能和相对热膨胀性能、杂质颗粒尺寸、等效基体韧性等都可能影响杂质颗粒失效形式,但是杂质颗粒直径增加、基体韧性降低必然降低材料强度。对于含氧化铝杂质颗粒的TiC-TiB_2装甲陶瓷,界面脱粘是杂质颗粒主要的失效形式。     

Fracture of high volume fraction ceramic particle reinforced aluminium under multiaxial stress

Circumferentially notched cylindrical bars of high volume fraction Al₂O₃ particle reinforced aluminium are tested in tension to probe the role of tensile stress triaxiality on damage and failure of such materials. The transverse strain is monitored with a specially designed video extensometer. A significant dependence of the peak average stress and failure strain on notch radius is observed. Finite-element simulations of the tests are conducted on the basis of a micromechanical model derived from earlier studies of damage and failure of these composites under uniaxial tensile deformation (Journal of the Mechanics and Physics of Solids 2009;57:1781). The simulations show that stress and strain distributions within the notched composite samples deviate significantly from predictions of Bridgman’s simplified analysis. Comparison with data shows that, whereas calculations capture satisfactorily the evolution of the average composite flow stress as a function of notch radius at small strains, the notched samples damage faster and fail at strains lower than predicted. Two phenomena may explain the discrepancy, namely (i) damage coalescence beyond a threshold level, and (ii) the incapacity of the matrix to sustain large hydrostatic stresses, which results from the presence of internal surfaces (cracked particles and possibly matrix voiding).     

Mechanical behavior of Al-Al2O3 MMC manufactured by PM techniques part I—scheme I processing parameters

Metal matrix composites (MMC) were manufactured using hot pressing followed by hot extrusion of aluminum (Al) powder reinforced by alumina (AI₂O₃) particles. Under tensile as well as compressive loads, a strength improvement of 64 to 100 % compared to the matrix material strength was obtained. The percent elongation to fracture ranged from 20 to 30%, which indicates good ductility as compared to the ductility of MMC manufactured by other techniques. Optical as well as scanning electron microscopy (SEM) examinations were used for characterization of the material microstructure and fracture behavior. Porosity retained in the microstructure was very limited in the case of pure aluminum billets. Microstructural examination revealed uniform distribution of Al₂O₃ particles in the Al-matrix. Under tensile loads, voids opened by decohesion between the matrix and reinforcement. Such behavior led to a decrease in strength properties of the MMC as a function of reinforcement volume fraction. The fracture surface is dominated by the ductile fracture features, that is, dimples. Voids were found to initiate at retained porosity sites at the AI/AI₂O₃ interface or in the matrix close to the interface due to stress concentration. The SEM revealed the formation of a complex fine subgrain structure. Such a polygonized structure is a major source of strengthening.     

Microstructure and wear characteristics of ATZ ceramic particle reinforced gray iron matrix surface composites

The alumina toughened zirconia(ATZ) ceramic particle reinforced gray iron matrix surface composite was successfully manufactured by pressureless infi ltration. The porous preform played a key role in the infi ltrating progress. The microstructure was observed by scanning electron microscopy(SEM); the phase constitutions was analyzed by X-ray diffraction(XRD); and the hardness and wear resistance of selected specimens were tested by hardness testing machine and abrasion testing machine, respectively. The addition of high carbon ferrochromium powders leads to the formation of white iron during solidifi cation. The wear volume loss rates of ATZ ceramic particle reinforced gray iron matrix surface composite decreases fi rst, and then tends to be stable. The wear resistance of the composite is 2.7 times higher than that of gray iron matrix. The reason is a combination of the surface hardness increase of gray iron matrix and ATZ ceramic particles and alloy carbides protecting effect on gray iron matrix.