NiTi形状记忆合金的动力学行为及其宏微观机制

It is possible for shape memory alloys to realize multiple-reversible energy absorption ability due to its unique property of super-elastic behavior and shape memory effect, which make it a promising material to be used in the impact protective area and need to a further study. In this proposal, systematically experiments and simulations on the complex phase transformation behevior and its micro-mechanism of NiTi shape memory alloys will be carried out. The experiment method and measurement techniques of laser shock as well as split Hopkinson pressure bar experiment (SHPB) will be developed. The effect of properties of material, stress, strain rate and temperature effect on the phase transformation and plastic deformation behavior of NiTi shape memory alloys will be discussed. In addition, the critical transition condition between two deformation modes will be obtained. Moreover, molecular dynamics simulation will be conducted to study the origination and evolution of atomistic structures. The effect of grain size, component proportion, defect, environment parameters and load parameters will be analyzed to obtain the mechanism of phase transformation. Diagram of phase transformation will be given out and the complex deformation modes as well as its mechanisms of NiTi shape memory alloys under high strain rate will be illuminated. The significance of this project is to give impetus to the application of shape memory alloys in the impact protective structure design area.

形状记忆合金独有的超弹性性质以及形状记忆效应使其在冲击加载过程中具有实现可逆多次冲击吸能的潜力，其在冲击防护领域的重要工程价值还有待进一步研究。本项目拟对镍钛（NiTi）形状记忆合金复杂相变行为及其微观机理开展实验与数值模拟研究。通过分离式霍普金森压杆（SHPB）实验以及激光驱动冲击加载实验，获取材料微结构参数、压力、应变率与温度对于NiTi形状记忆合金相变行为与塑性变形行为的影响规律，得到两种变形模式的临界转变条件。与此同时，采用分子动力学模拟（MD），分析包括晶粒尺寸、组分比例、缺陷等在内的材料参数，环境参数以及载荷参数等对于NiTi形状记忆合金在加载过程中原子结构形核及演化规律的影响，获得NiTi形状记忆合金相图，阐明高应变率条件下是否发生相变行为及其内在机理，得到NiTi形状记忆合金相变行为的微观机制。预期的研究成果将有望推动形状记忆合金在冲击防护结构设计中的应用。

材料与结构的动力学响应行为是冲击防护结构设计的基础，一直以来都是冲击动力学领域的研究热点。传统的吸能方式主要利用材料的压溃、破碎等变形与失效方式耗散能量，不具备多次冲击吸能的能力，难以满足日益增长的先进冲击防护材料与结构设计需求。形状记忆合金（Shape Memory Alloys, SMA）独有的超弹性性质以及形状记忆效应使其在冲击加载过程中具有实现可逆多次冲击吸能的潜力。目前针对SMA相变行为的研究以实验为主，对于其微观机理研究相对较少。本项目针对典型SMA材料NiTi形状记忆合金的复杂相变行为开展了相关研究。采用分子动力学模拟，分析了晶粒尺寸,缺陷等参数对于原子结构演化历程的影响，阐述了晶界占比，缺陷对于相变行为以及塑性变形行为竞争机制的影响规律。同时，获得了高速冲击条件下，相变行为对于NiTi层裂行为的影响，期望为可重复吸能结构材料设计提供一定理论基础。

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