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《Acta Metallurgica Sinica》 2018-09
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Investigation of Strain Rate Effect by Three-Dimensional Discrete Dislocation Dynamics for fcc Single Crystal During Compression Process

GUO Xiangru;SUN Chaoyang;WANG Chunhui;QIAN Lingyun;LIU Fengxian;School of Mechanical and Engineering,University of Science and Technology Beijing;Beijing Key Laboratory of Lightweight Metal Forming,University of Science and Technology Beijing;Applied Mechanics Lab.,School of Aerospace Engineering,Tsinghua University;  
Microelectromechanical systems(MEMS) have become increasingly prevalent in engineering applications.In these MEMS,a lot of micro-components,such as thin films,nanowires,micro-beams and micropillars,are utilized.The characteristic geometrical size of those components is at the same scale as that of grain,the mechanical behavior of crystal materials exhibits significant size effect and discontinuous deformation.In addition,those MEMS are often subjected to high strain rate at work,such as collision and impact loading.The coupling deformation characteristics of small scale crystals and high strain rate makes their mechanical behavior more complicated.Accordingly,investigation of the effect of the strain rate on crystal materials at micron scale is significant for both the academia and industry.In this work,a plastic deformation model of fcc crystal under axial compression was developed based on three-dimensional discrete dislocation dynamics(3 D-DDD),which considered the influence of externally applied stress,interaction force between dislocation segments,dislocation line tension and image force from free surface on dislocation movement during the process of plastic deformation.It was applied to simulate the plastic deformation process of a Ni single crystal micropillar during compression under different loading strain rates.3 D-DDD and theoretical analysis are carried out to extensively investigate the effect of strain rate on flow stress and deformation mechanisms during plastic deformation process of crystal materials.The results show that the flow stress and the dislocation density increased with the loading strain rate.In the case of low strain rate,the flow stress was dominated by the activation stress of FreakRead(FR) source in plastic deformation.With the increase of strain rate,the contribution of activation stress of FR source to the flow stress decreases and the effective stress gradually dominated the flow stress.Under high strain rate loading,with the increase of the initial FR source,the dislocation density also increased at the same strain correspondingly,which makes it easier to meet the requirement of the loading strain rate,so the flow stress is smaller.In addition,under the low strain rate loading,a few activated FR sources can meet the requirement of the plastic deformation,a single slip deformation come up as a result.While,as the loading strain rate increases,more and more activated FR sources would be needed to coordinate the plastic deformation,the deformation mechanisms of the single crystal micropillar transformed from single slip to multiple slip.
【Fund】: 国家自然科学基金项目No.51575039;; 国家自然科学基金委员会-中国工程物理研究院联合基金项目No.U1730121~~
【CateGory Index】: TG146.15;O772
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