Buckling and collapse of pseudoelastic NiTi tubes under bending
Buckling and collapse of pseudoelastic NiTi tubes under bending
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DOI：
10.1016/j.ijsolstr.2019.12.017
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发表时间：
2019-12
影响因子：
3.6
通讯作者：
Karlos Kazinakis;S. Kyriakides;Dongjie Jiang;Nathan J. Bechle;C. Landis
中科院分区：
文献类型：
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作者：
Karlos Kazinakis;S. Kyriakides;Dongjie Jiang;Nathan J. Bechle;C. Landis
伪弹性镍钛结构部件已被证明表现出拉伸/压缩不对称性。在拉伸状态下，相变会引起近 7% 的局部应变，这些应变在几乎恒定的应力下传播，而在压缩状态下，相变会在明显更高的应力下导致硬化，应变更小且增长均匀。管材的弯曲使其横截面呈椭圆形，这种非线性会降低弯曲刚度并导致不稳定，从而导致倒塌。本文通过实验和分析来研究这些几何非线性与中等直径厚度比的伪弹性镍钛管在弯曲情况下的复杂材料行为之间的相互作用。对直径与厚度之比为 18.7 的管材进行的实验表明，相变导致受拉侧马氏体的几个分散的高应变带状图案形核。带合并成相交菱形的区域经历了过度的局部椭圆化，导致在相对较低的整体管曲率下发生屈曲和塌陷。弯曲实验通过有限元模型与定制的伪弹性 NiTi 本构模型相结合进行模拟，该模型允许马氏体相发生塑性变形。该分析再现了矩端旋转响应以及高应变菱形图案的成核和演化。形成这种图案的区域表现出椭圆化的加速增长，从而降低了局部弯曲刚度。在存在小的几何缺陷的情况下，这种退化会演变成扩散局部椭圆化形式的屈曲，从而导致塌陷，从而否定镍钛合金的可恢复性能。参数研究表明，随着管 D/t 的增加，材料和几何非线性之间的相互作用变得更强，使得屈曲对缺陷更加敏感。
Pseudoelastic NiTi structural components have been shown to exhibit tension/compression asymmetry. Under tension, phase transformation induces localized strains of nearly 7% that spread under nearly constant stress, while under compression the transformation leads to hardening at significantly higher stress, the strain is smaller and grows homogeneously. Bending of tubes ovalizes their cross-section, a nonlinearity that reduces the bending rigidity and precipitates instabilities that can lead to collapse. This paper uses experiment and analysis to examine the interaction of these geometric nonlinearities with the complex material behavior of pseudoelastic NiTi tubes of moderate diameter-to-thickness ratios under bending. An experiment on a tube with a diameter-to-thickness ratio of 18.7 shows that transformation causes the nucleation of several dispersed high strain banded patterns of martensite on the tensioned side. The zone where the bands coalesce into intersecting diamonds undergoes excessive local ovalization causing buckling and collapse at a relatively low overall tube curvature. The bending experiment is simulated with a finite element model coupled with a custom constitutive model of pseudoelastic NiTi that allows for plastic deformation of the martensitic phase. The analysis reproduces the moment-end rotation response, and the nucleation and evolution of the high strain diamond shaped patterns. Zones that develop such patterns exhibit accelerated growth of ovalization that degrades the local bending rigidity. In the presence of small geometric imperfections this degradation evolves into a buckle in the form of diffuse local ovalization that precipitates collapse that can negate the recoverable property of NiTi. Parametric studies show that as the tube D/t increases, the interaction between the material and geometric nonlinearities becomes stronger making buckling more imperfection sensitive.