相变对TiNi合金薄壁管中波速的影响

Effect of phase transformation on wave speeds in TiNi alloy thin-walled tube

形状记忆合金在受到强冲击荷载作用时会发生相变,而相变对其结构件的动态力学响应影响显著。本文采用同时考虑静水压力和偏应力影响的相变临界准则,推导了增量型的相变本构模型。基于广义特征理论,得到了复杂应力状态下特征波速的解析表达式。特征波速不仅和材料本身的力学参数(如拉压不对称性和混合相的模量)有关,还和材料所处的应力状态有关。对因相变导致体积膨胀的TiNi合金而言,拉压不对称性系数的增大会提高慢波的波速,而对快波几乎没有影响。在相变椭圆的短轴处(α=90°),慢波的波速最低,并随混合相无量纲模量的增大而显著减低,混合相无量纲模量由2增加至5时,波速降低幅度为36.2%,而快波的波速达到最大值c_(0),和混合相的模量无关;在相变椭圆的长轴处(α=180°),慢波的速度达到最大值,而快波的波速达到最小值c_(2)。

Shape memory alloys undergo phase transformation under strong impact loads,and the phase transformation has a significant impact on the dynamic mechanical response of their structural components.Based on the phase transformation critical criterion considering both hydrostatic pressure and deviatoric stress effects,an incremental constitutive model of phase transformation is derived.The analytical expression of characteristic wave speed under complex stress state is obtained based on the generalized characteristic theory.The characteristic wave speed is not only related to the mechanical parameters of the material itself(such as the tension-compression asymmetry and the modulus of the mixed phase),but also related to the stress state of the material.For TiNi alloys with volume expansion due to phase transformation,the increase of tensile-compressive asymmetry coefficient will increase the wave speed of slow waves,while having almost no effect on fast waves.At the short axis of the phase transformation ellipse(α=90°),the wave speed of slow waves is the lowest and decreases significantly with the increase of the dimensionless modulus of the mixed phase.When the dimensionless modulus of the mixed phase increases from 2 to 5,the wave speed decreases by 36.2%,while the wave speed of fast waves reaches the maximum value c_(0),which is independent of the modulus of the mixed phase;at the long axis of the phase transformation ellipse(α=180°),the speed of slow waves reaches the maximum value,and the wave speed of fast waves reaches the minimum value c_(2).