基于位错可动性及与表/界面相互作用的耗散型晶体塑性模型研究

Micro- and nano-crystals usually possess mechanical properties superior to their coarse-grained counterparts. However, their behaviors during plastic deformation show some abnormal characteristics such as size effect of Hall-Petch and inverse Hall-Petch effects, partial recovery at room temperature and strain burst, which makes the classical plasticity no longer applicable for characterizing tools. According to the available results, both experimental and numerical, various dissipative mechanisms such as glide of lattice dislocation, dislocation nucleation and absorption at surfaces and interfaces, and grain boundary sliding are involved in the plastic deformation of micro- and nano-crystals. The existent plasticity models nevertheless usually capture only part of the mechanisms and are still far from those revealed. In the present project, the applicants are thus motivated, on the basis of their previous energetic models, to investigate the size effect of dislocation mobility, interaction between dislocations and penetrable surface/interfaces, and grain boundary sliding with stick-slip features. Equations for the evolution of dislocation density will be established so as to formulate new models for crystal plasticity with all the new parameters that can be estimated from the physical deformation process. Outcome of the research will help not only to characterize the mechanical properties of micro- and nano-crystals precisely but also to clarify and understand better the underlying physical mechanisms responsible for the abnormal plastic behaviors. In turn, the results may help to promote the applications and development of micro- and nano-crystals.

微纳晶体材料具有很多优于粗晶材料的力学性质，但同时塑性变形行为具有Hall-Petch尺寸效应或反Hall-Petch尺寸效应、塑性变形部分回复以及应变突跳等反常特征。这使得经典晶体塑性理论无法对微纳晶体变形进行准确表征。已有研究成果揭示的微纳晶体塑形变形的多种机理（如晶体位错滑移、表/界面发射吸收位错、晶界滑动等），而现有模型通常仅考虑了部分机制，与实验模拟的结果仍有相当差距。因此本项目拟在申请人前期有关储能模型基础上，着重研究位错可动性系数的尺寸效应、穿透表/界面和滑动晶界与晶体位错的相互作用，以便考虑不同变形机理随尺寸变化的可能转换，建立位错密度的演化方程，从而建立考虑耗散尺寸效应并且相关物理力学参数可估测的新晶体塑性模型，并分析典型问题加以验证。相关研究结果将有助于实现对微纳晶体力学性质的精确表征，也有助于加深理解微纳晶体塑性变形反常行为的物理机制，并可能推动微纳晶体的发展与应用。

微纳晶体塑性变形具有如应变突跳、屈服强度尺寸效应、塑性恢复等反常行为，经典塑性理论已无法对此加以表征。过去二十多年来，虽然已发展了各种应变梯度理论，但存在新参数多难以确定的问题，而且仍然很难表征微纳晶体塑性变形的一些反常效应。对此，本项目根据大量实验所揭示的滑移位错、表界面过程等变形机理，考虑位错可动性及其与表面界面的相互作用，发展新的晶体塑性理论。其中根据位错被表面吸收形成台阶的事实以及该过程的耗能性质，建立新的表面塑性本构关系。根据位错在界面处可能穿透界面的事实，建立的穿透准则以及界面塑性本构关系。基于这些结果，结合以位错为基础的应变梯度理论，进而建立了新的晶体塑性理论，可有效表征微纳晶体塑性变形的尺寸效应，且所引入的新参数更容易估计或确定。此外，将位错形核和可动性等应用于粘着接触研究，探索了滑动前兆的物理本质，建立了颗粒滑动摩擦定律。对所建立的界面本构退化到经典理论，结合珍珠母类材料几何结构特点，讨论了界面互锁结构对桥联增韧的影响。基于该项目研究，目前已发表高质量论文7篇，培养研究生10名。