Analysis of phase transformation from austenite to martensite in NiTi alloy strips under uniaxial tension

Phase transformation from austenite to martensite in NiTi alloy strips under the uniaxial tension has been observed in experiments and numerically simulated as a localized deformation.This work presents an analysis using the theory of phase transfor- mation.The jump of deformation gradient across the interface between two phases and the Maxwell relation are considered.Governing equations for the phase transformation are derived.The analysis is reduced to finding the minimum value of the loading at which the governing equations have a unique,real and physically acceptable solution.The equa- tions are solved numerically and it is verified that the unique solution exists definitely. The Maxwell stress,the stresses and strains inside both anstenite and martensite phases, and the transformation-front orientation angle are determined to be in reasonably good agreement with experimental observations.     

应力集中的“善”与“恶”——————漫谈应力集中的利用和防治

 在日常生活中,应力集中的应用给生活带来了方便. 在工 程结构中,应力集中的存在,给结构带来了危害. 扬应力集中 之“善”,抑应力集中之“恶”,是人们的追求.     

负压激励下含椭圆孔高弹体的屈曲分析

基于数值模拟与理论分析,研究了含周期性椭圆孔二维结构的屈曲行为。针对不同的屈曲模态,建立理论模型进行模态分析。结果表明,改变孔的几何参数,椭圆孔结构的屈曲模态会随之发生转换,理论分析与数值结果吻合良好。此外,在数值模拟中,与位移加载不同,负压激励下的单胞需要考虑力边界条件的修正,以确保其满足完备性条件。已有工作在单胞选择中常存在问题,导致错误结果。针对上述问题研究了不同单胞所对应的边界条件,并结合有限结构进行了分析与讨论。     

单向拉伸镍钛合金带从奥氏体到马氏体的相变分析

单向拉伸镍钛合金带中从奥氏体到马氏体的相变已在实验中观测到,并被看作为局部变形进行了数值模拟．该文采用相变理论对其进行分析,考虑了两相界面处变形梯度的跳跃以及Maxwell关系,导出了相变的控制方程．相变分析归结为寻求载荷的最小值,使在该值下控制方程具有唯一的、物理上可以接受的实数解．控制方程被数值求解,证明了该唯一解确实存在．相变的Maxwell 应力,马氏体相与奥氏体相内的应力与应变,以及相边界的倾角都可求出,并与实验所观测到的结果相吻合．