预应力对多晶铁冲击行为影响的微观模拟研究  

Influence of prestress on shock behavior of polycrystalline iron via atomistic simulations

作　　者：任国武[1] 张世文[1] 范诚[1] 陈永涛[1] 

机构地区：[1]中国工程物理研究院流体物理研究所,绵阳621999

出　　处：《物理学报》2016年第19期219-224,共6页Acta Physica Sinica

基　　金：国家自然科学基金(批准号:11272006;11272297);中物院发展基金(批准号:2014B0201018)资助的课题~~

摘　　要：冲击加载铁动力学响应是当前冲击波领域金属材料塑性和相变行为研究最为关注的焦点之一.本文采用分子动力学模拟方法开展预应力作用下冲击加载多晶铁的动力学行为研究.模拟结果表明,随着预应力的增加,导致弹塑转变应力(Hugoniot弹性极限)和冲击波速度提高,符合已有的理论分析结果.微观晶体结构表征则发现较大的预应力导致剪应力大于屈服应力,塑性弛豫时间缩短,加快多晶铁α→ε相转变.进一步通过与平面及柱壳纯铁冲击加载获得的自由面速度剖面对比分析,证实了模拟结果.Plasticity behavior and phase transition of metal Fe subjected to shock loading have attracted considerable attention in shock physics community, in particular for underlying relationship between them. Experimental examinations and atomistic simulations on shocked Fe have displayed a three-wave structure： elastic wave, plastic wave and transformation wave. However, these studies are primarily limited to the one-dimensional planar case. Recently, owing to the rapid development of experimental techniques, investigating dynamic property of shocked metal has extended to the multidimensional loading conditions, such as cylindrical or spherical shocks. In this regard, fruitful findings are achieved, for example, twinning ratio in polycrystalline Fe under implosive compression is found to be much higher than that under planar shock, implying that the the complex stress state plays a critical role.In this paper, we explore the effects of prestress on plasticity and phase transition of shocked polycrystalline iron. The imposed presstress normal to the impact direction in one-dimensional planar shocking represents the varying deviatoric stress, and does not nearly affect the principal stress. The utilized empirical potential for iron could describe the plasticity dislocation and phase transition very well. The simulations show that as the prestress increases, the shock speed at elastic stage and Hugoniot elastic limit increase, which is in accordance with the theoretical analyses based on shock wave theory and experimental measurement. Meanwhile the plastic wave speed increases more quickly and catches up with the transformation wave more easily, resulting in a steep shockwave front. Atomistic snapshots show that plasticity dislocation stemming from the grain boundary precedes phase transition, where most of BCC atoms are transformed into the HCP atoms and shear stress significantly decreases. Further observations from these images find that plastic zone becomes narrower with increasing prestress, representing a shorter

关 键 词：预应力 多晶铁 塑性 相变 

分 类 号：O341[理学—固体力学]