圆柱薄壳的动相变屈曲行为

Phase transformation dynamic buckling behaviors of pseudo-elastic TiNi shells under axial impact

利用MTS809材料试验机对TiNi圆柱薄壳进行了轴向动渐进相变屈曲实验,对轴向冲击下处于伪弹性状态的TiNi合金柱壳的动相变屈曲行为进行了数值模拟研究。结果表明,不同的加载强度将会激发出柱壳不同的动屈曲响应模态。当冲击速度较高时,柱壳两端首先形成轴对称环形相变屈曲波纹,并产生应力平台;随着马氏体含量不断增加,环形相变屈曲波纹逐渐贯穿整个壳体,名义应力缓慢抬升;当名义应变超过一定阈值时,对称环形屈曲模态突变为非轴对称块状屈曲模态,名义应力大幅下降。撞击速度为40 m/s的算例(含10%随机缺陷)与S.Nemat-Nasser等的实验结果很好吻合,说明本文中计算模型、方法和结果的有效性经过了实验的考核。结果还表明,相变耗能是TiNi柱壳吸收冲击能量的主要机制,适合制作可重复使用的高效吸能元件,并给出了相应的理想厚径比。

A series of quasi-static axial compression tests were conducted on pseudo-elastic TiNi shells by an MTS 809 material testing system to observe their dynamic progressive buckling responses. And numerical simulations were carried out to analyze phase transformation dynamic buckling behaviors of the pseudo-elastic shape-memory alloy shells under short pulse loading. It is indicated that TiNi shells have different buckling modes under different load levels. The buckling of shells begins with the formation of axisymmetric rings under high load speeds and produces a stress plateau. With the gradual increase of martensite fraction, ring phase transformation buckling travels gradually through the whole shell and the nominal stress increases slowly. When the nominal stress exceeds a certain threshold, the axisymmetric ring buckling mode transforms into a nonsymmetrical massive buckling mode and the nominal stress decreases dramatically. The calculation sample with the impact velocity of 40 m/s and the random defect of 10% is in agreement with the experiments by Nemat-Nasser S, et al. The results show that phase transformation energy dissipation is the main mechanism of TiNi shells absorbing impact energy and TiNi shells are suitable for reusable efficient energy dissipation mechanism. And the corresponding perfect diameter-thickness ratio of TiNi shells was proposed.