Study On Predicting The Deformation And Fracturing Behaviors Of Particle Reinforced Metal Matrix Composites By Multiscale Method

Particle reinforced metal matrix composites(PRMMCs)have become one of the most potential candidate materials in industrial and experimental design due to their excellent physical and mechanical properties.Besides,their advantages in designability of material properties,preparation technology and preparation cost help increasing the applications in engineering and structural area.In order to meet the increasing application requirements of PRMMCs,it is necessary to conduct more scientific and comprehensive research on deformation and failure mechanism of PRMMCs.The fracture behavior of PRMMCs is essentially a multi-scale problem including micro-scale cracks and macro-scale cracks.In this study,we constructed a micro-nano/meso-scale sequential coupling multi-scale model for PRMMCs based on the theories of both peridynamics(PD)and molecular dynamics(MD).A systematical study is carried out to uncover the deformation and crack propagation of PRMMCs under quasi-static and dynamic loading.The main research contents are as follows:(1)Atomic models of PRMMCs are constructed to reveal the micro-deformation and failure mechanism of composite.MD method is employed to build simulated models of nano-ceramic particle-reinforced polycrystalline aluminum matrix composites,and discuss the relevant performances.The results show that inclusions in composites act as strong obstacles to the crystal movement and the formation of shear bands,leading to the enhancement of the PRMMCs.When considering the effect of particle distribution,it is found that inhomogeneous distribution is more liable to block the slip of local dislocations,which inducing the localized strain distribution in the composite,and consequently leading to the enhanced strength and increasing ductility.(2)A micro-mesoscale sequential multi-scale model for PRMMCs is contructed,and the corresponding reliabilily is verified by numerical simulations.In this model,MD simulation is employed to characterize the interfacial properties firstly.Afterwards,the obtained result is parameterized into the required bond-stretch constitutive function in the PD model.On this basis,the calculated program of PRMMCs is developed for the multi-scale simulation.The PD theory is applied to study the deformed and failure mechanism of PRMMCs,thereby constructing a micro-mesoscopic sequential coupling multi-scale model for PRMMCs,and solving the discontinuous cracking problems which can not be reproduced by traditional continuum mechanics theory.To validate the accuracy of the model,we evaluate the performance of the model on both quasi-static and dynamic problems.The results show that the constructed multiscale model has general applicability for the simulation and prediction of the mechanical properties and fracture behaviors of PRMMCs.(3)The mechanisms of deformation and fracture propagation of PRMMCs under quasi-static loading are investigated based on the multi-scale model.In order to reproduce the effect of PRMMCs particles on the crack initiation and propagation,various particle shapes and interface properties are taken into account.The results show that the shape of the particle has a significant effect on the stress concentration state inside the material,consequently affects the fracture properties of the composite.Moreover,the dominant failure mode may change by modifying the particle angle,two fracture ways,i.e.,failure of matrix and the interface debonding,can be observed correspondingly.Based on the constructed multi-scale model,the numerical simulation can reproduce the whole process of the deformation,interface debonding and crack propagation of PRMMCs under quasi-static loading,which overcomes the disadvantages that the traditional experiments cannot observe and study the relevant crack propagation mechanism.Thus,the model has advantages in characterizing the crack initiation and propagation of PRMMCs.(4)The rate-dependent constitutive model is introduced to reveal the dynamic cracking growth mechanism of PRMMCs under different loading rates based on the multi-scale model.In this study,the modified Johnson-Cook model is introduced into the PD model,and the strain rate effect of the failure mode of PRMMCs is considered.The predicted results and the experimental results are in good agreement,which validates the applicability of the constitutive model.When analyzing the mechanical response of the material under various loading rates,it is found that the change of loading strain rate has significant effects on the overall mechanical properties,i.e.,strength and ductility,of the composite.Once the strain rate reaches a certain threshold,the stress and strain state of the material would change,and the failure mode will transfer from the failure of the matrix to the break of the reinforcement.Besides,the increasing particle volume fraction may make the particles more likely go broken.The simulation can fully track the whole process of deformation,particle broken and dynamic crack propagation of PRMMCs,solving the difficulty of studying the dynamic crack propagation mechanism of PRMMCs through in-situ observation in traditional experiments.Thus,this multi-scale model has advantages in characterizing the dynamic crack propagation of PRMMCs.(5)A graphene/Si C particle reinforced aluminum matrix model is constructed,and the strengthening effect of graphene on the overall mechanical properties of PRMMCs is discussed.Firstly,we build a graphene-encapsulated silicon carbide particle reinforced polycrystalline aluminum matrix composite model based on MD theory for simulation.The results show that graphene mainly has two effects on the mechanical properties of composites,i.e.,reducing the atomic potential energy of the interface and increasing the elastic modulus of the particles,consequently improving the strength of the composite and losing the ductility.Secondly,we build a finite element model for discussion.At this scale,the strengthening effect of graphene maily contains three parts,i.e.,thermal mismatch,Orowan and fine-grain strengthening mechanisms.The results show that a better enhancing effect of encapsulating graphene can be achieved with a larger volume fraction and a smaller particle size.