基于二阶功表征的微尺度晶体材料应变突变判据研究

Mechanical properties of crystalline material at microscale are very different from that at macroscale. Specifically, plastic flow of microscale crystalline material is characterized by the intermittent strain bursts that behavior much similarly to the plastic instabilities of bulk crystals. Accurate predictions of the strain burst phenomenon are vitally significant for the plastic forming of microscale materials and the evaluation of mechanical property. In this regard, we propose a strain burst criterion based on the conservation of energy in the course of plastic flow. Concrete research content including following: (1) we systemically study the relation between the second-order work and strain burst by using the theoretical analysis based on the conservation of energy and numerical simulations based on crystal plasticity finite element method, and then check the applicability of Hill’s stability condition on the strain burst of microscale crystalline materials; (2) The strain burst criterion described by the second-order work is proposed and then is incorporated into the intermittent constituent mode. In order to check the reliability of second-order criterion, we perform three-dimensional finite element analysis of the model, and compare the simulated strain burst phenomenon with available experiments. (3) We investigate the relation between the kinetic energy and second-order work in the context of the occurrences of strain burst, and then reveal the physical meaning of the strain burst criterion described by the second-order work. This project aims to propose an accurate and widely used criterion for strain burst, in order to provide the theoretical criterion for the strain burst of microscale metals subjected to the external loading in the practical working conditions.

微尺度晶体材料的力学行为不同于宏观尺度，其塑性应变会发生多次间歇性突变，表现出类似于宏观材料的塑性失稳形态。准确预测应变突变现象的发生对于微尺度晶体材料的塑性加工成型与力学性能评估有着重要的科学意义。本项目从间歇性塑性流动的能量守恒出发，提出了描述应变突变现象的力学判据。研究内容包括：（1）采取基于能量守恒原理的理论研究与晶体塑性有限元分析两种手段，研究应变突变与二阶功的关系，检验Hill稳定条件对于应变突变问题的适用性。（2）提出基于二阶功表征的应变突变判据，建立基于该判据的间歇性晶体塑性理论，进而结合有限元方法，对微尺度晶体材料的应变突变现象进行模拟分析，通过与现有实验进行对比，检验二阶功判据的可靠性。（3）考察应变突变条件下二阶功与系统动能的关系，揭示二阶功判据的物理意义。本项目旨在提出更加准确可靠的应变突变判别方法，力求为实际工况中微尺度材料应变突变问题的分析提供理论判据。

亚微米尺度金属单晶在塑性变形中会发生应变突变。项目着眼于亚微米尺度金属单晶塑性变形中的应变突变特性，采取基于能量守恒原理的理论研究与晶体塑性有限元模拟两种手段，建立了微尺度金属单晶应变突变与二阶功之间的关系，检验了Hill稳定条件对于微尺度金属应变突变问题的适用性。进而，提出了基于二阶功描述的应变突变判据，并进一步揭示该判据蕴含的物理意义。项目建立的应变突变判据，可为实际工况中微尺度晶体材料出现的应变突变现象提供可靠的理论判据。该研究成果在探究将经典晶体塑形理论拓展至亚微米尺度方面具有重要的科学意义。

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