Multi-scale Modeling And Simulation Of The Mechanical Properties Of Particle Reinforced Metal Matrix Composites

The research objects of this paper are Zirconia Toughened Alumina particle?ZTA_p?and Alumina particle reinforced Fe alloy matrix composites.Fe matrix composite materials have both high strength of the ceramic and good toughness of the metal matrix after the addition of ceramic particles into the metal,and have good abrasion resistance.Ceramic particle reinforced Fe composites are expected to be applied to mining,cement,electric power and environmental protection fields as wear-resistant materials of the mechanical equipments,used in scraper conveyor groove,crusher machinery and other easy-to-wear parts,thus have broad application prospects and commercial values.Compared with single-phase materials,the structures of multiphase ceramic particle reinforced metal matrix composites are characterized by non-uniform,discontinuous and non-linear performance at the microscopic scale,therefore their mechanical behavior is much more complicated.Previous studies have shown that many factors,such as size,content,shape and type of the ceramic particles,the interface bonding between the ceramic particles and the metal matrix,and the microscopic defects in the composite will affect the overall mechanical properties of the composites.There dose not exist a simple proportional relationship between these factors and the mechanical properties of the composites.Take the interfacial bonding property for an example,in some specific cases,it is desired that the interface be cracked by bearing loads so that the composite material could absorb more energy before fracture thus has higher toughness.On the contrary,in some cases,the cracking of the interface will accelerate the destruction of the composite material,bringing great potential safety hazards to the equipment and components.By systematically adjusting and regulating these factors,we can get specific composite materials which have desired comprehensive performance according to requirements of use and suitable for actual working conditions.There are some difficulties in measuring the interfacial properties between the ceramic particles and the metal matrix experimentally,because the composite materials to be tested needs to be machined before the measurement to obtain specimens with appropriate size and shape,during which additional stresses are introduced,resulting in low accuracy of the interfacial performance.At the same time,the experimental results are greatly affected by the sensitivity of the instrument as well as the operational level of laboratory staff,which means the repeatability of the experiment is not high.Computer simulation technique of the mechanical properties of composites has been increasingly used in the study of composite materials because of its convenient operation and the ability to predict results.The computer simulations of the mechanical properties of the composites can be conducted on different scales.Based on continuum mechanics theory,macroscopic simulation assumes that the material is continuous and isotropic,and the operations are simple and convenient.However,the accuracy of the results is limited and depends on many factors such as mesh and element size.Microscopic simulations are carried out from the viewpoint of atoms and molecules,discussing the role of electrons and the force field in which the atoms are located,thus it has good accuracy.However,using microscopic simulations,the simulated material size and area are limited.At this point,multi-scale modeling and simulation method combining macroscopic and microscopic dimensions came into being.Having both the efficiency of macroscopic simulation and the accuracy of microscopic simulation,multi-scale simulation method is more suitable to predict the mechanical properties of composite materials which can be regarded as a uniform material macroscopically,while the microscopic microstructure is not uniform.In this paper,the author makes full use of theoretical knowledge of the strengthening effect of the ceramic particles to the metal matrix.With the help of various strength and failure models applicable to different kinds of materials,such as the J-H model and Weibull model of the ceramic materials,the hardening model and Mott distribution model of the metal materials,the influencing factors of the mechanical properties of ZTA_p/Fe45 and Al₂O_3p/Fe45 composites are studied using a combination of simulation and experimental verification methods.The effects of the properties of the particles,such as size,volume fraction,shape,the interfacial bonding properties between the particles and the matrix,and the defects in the materials to the mechanical properties of the composite were analyzed and summarized systematically.The main results are as follows:1.The parameters of the ZTA particles and the interfacial properties between the particles and the matrix together affect the tensile behavior of the ZTA_p/Fe45composites.When it comes to particle volume fraction,to abtain ZTA_p/Fe45composites with high yield limit,the volume fraction of the ZTA particles should be high enough yet not too high to cause a dramatic drop in the critical strain of the composites.The interface bonding strength between the particles and the matrix should be strong enough to increase the yield limit and the critical stress of the composites,and to reduce the failure probabilities of the material due to debonding of the interface.In order to obtain ZTA_p/Fe45 compoistes with the best comprehensive performance,the optimum volume fraction of the ZTA particles is approximately 20%and the best interface bonding is strong.In terms of the particle shape,using sharp-angled particles represented by square particles can effectively improve the yield limit,the critical strain and stress,the fracture strength and the ability to withstand damage of the ZTA_p/Fe45 composites,thus the compoistes are suitable for wear and other harsh working conditions.ZTA_p/Fe45 composites containing elliptical particles has a larger elastic modulus than composites containing sharp-angled particles,the former is suitable for working conditions with small deformation.When the particle size lies within the range of 1.4³.0mm,ZTA_p/Fe45 composites containing small size particles possess higher yield limit and stronger resistance to failure,while composites containing large size particles have higher elastic modulus.2.With an increase in the ZTA particle volume fraction,the fracture probability of ZTA particle decreases slightly,and the number of cohesive interface debonding increases.In ZTA_p/Fe45 composites with cohesive interface,the elliptical particles result in maximum extreme equivalent stresses and the square particles lead to minimum extreme stresses.The extreme stresses and the area of stress concentration of the ZTA_p/Fe45 composites increase with increasing ZTA particle size.The fine dispersed ZTA particles have a stronger deflection effect on the load therefore the stress distributions inside the composites are more uniform and the matrix has a better strengthening effect,while coarse ZTA particles are more likely to cause local stress concentration of the matrix and to increase the probability of damage.In composites with weak interface,the matrix around the interface cracking tip is more susceptible to yield failure.The fracture probability of the ZTA particles decreases with increasing bonding strength of the cohesive interface.3.The molecular dynamics simulation results of the Al₂O_3p/Fe interface show that the maximum tensile stress and the maximum shear stress of the interface are1.4770Gpa and 0.3294GPa,respectively.The ultimate tensile displacement and ultimate shear displacement of the interface are 14.7?and 17.3?,respectively.The influences of the ZTA particle parameters on the impact properties of the ZTA_p/Fe45composites are as follows:In compoistes containing single size particles,the impact energy absorption of the composites increases with increasing size of ZTA particles,but the area of fracture zone of the composites increases as well.The impact toughness of composites containing single size particles is higher than that of composites containing grading size particles.The maximum equivalent stress value was observed in the composites containing grading size particles due to the squeezing and embedding arrangement of the particles and the matrix is most susceptible to yield failure.With an increase of the volume fraction of the ZTA particles,the work hardening rate of the ZTA_p/Fe45 composites increases,the void nucleation becomes earlier,thus the impact energy absorption of the ZTA_p/Fe45 composites decreases.There is no obvious relationship between the maximum equivalent stress magnitude and the volume fraction of the particles,but larger area of stress concentration region was observed in composites with low volume fraction of ZTA particles.As the volume fraction of the ZTA particles increases,the area of fracture zone of the composites increases due to the deflection effect of the particles on the impact load.4.The multi-scale simulated impact properties of the ZTA_p/Fe45 composites are compared with the experimental data,and the results show that the simulated variation trends of impact energy absorption of the composites with the size and the volume fraction of the ZTA particles as well as the failure mode and the area of fracture zone of the composites agree well with the experimental results.However,the simulated impact energy absorption is slightly lower than that of the experiment.After analysis,it can be seen that there are two main reasons:First,Mott distribution model is used in the simulation to describe the defects inside the matrix material.When the instantaneous stress of an element of the matrix material reaches its ultimate stress,the element fails immediately.However,the volume of the element in the simulation is larger than some defects in real material,therefore composites in the simulation are more prone to damage,coupled with lower impact energy absorption.Second,the mechanical properties of Al₂O₃ particle are used to approximately replace the performance of ZTA,the impact energy absorption is underestimated due to the neglect of the phase transformation toughening effect of ZrO₂.5.When the Al₂O_3p/Fe composite is subject to wear load of the abrasive diamond asperity,as the abrasive diamond asperity moves along,the metal atoms on the surface of the composite accumulate at the front side of the asperity.The rotation and downward movement of the upper Al₂O₃ particles avoid the direct contact between the abrasive asperity and the metal atoms below the Al₂O₃ particles,in this way,the wear rate of the metal material is reduced.With an increase of the horizontal sliding velocity v_x and the normal load f_z of the abrasive diamond asperity,there is a decreasing trend in the average friction coefficient and the surface roughness of the Al₂O_3p/Fe composites,and the total number of worn atoms increases which indicates that the wear resistance of the composites decreases.With an increase of the volume fraction V_f of the Al₂O₃particles,the total number of worn atoms first increases and then decreases.The highest wear rate of the composite is observed at a V_f of 25%.When V_f exceeds 25%,the wear rate of the composite decrease with increasing V_f.Under larger normal load f_z of the abrasive asperity,the plowing effect of the abrasive asperity plays a dominant role.When the volume fraction V_f of Al₂O₃ particles is large,the blocking effect of the Al₂O₃ particles plays a major role.The purpose of this paper is to establish a general theoretical calculation model and to predict the interfacial properties,impact properties and abrasive wear properties of ceramic particle reinforced metal matrix composites by multi-scale modeling and simulation.After the experimental results are obtained,the theoretical model is modified to improve the accuracy and practicability of the model.This paper provides guidetance to the research and application of advanced ceramic particle reinforced metal matrix composites.