Buckling and collapse of pseudoelastic NiTi tubes under bending

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 constant stress, while compression the leads hardening at significantly higher strain is smaller and grows homogeneously. Bending tubes ovalizes their cross-section, a nonlinearity reduces bending rigidity precipitates instabilities can lead collapse. This paper uses experiment analysis examine interaction these geometric nonlinearities with complex material behavior pseudoelastic moderate diameter-to-thickness ratios bending. An on tube ratio 18.7 shows causes nucleation several dispersed high banded patterns martensite tensioned side. The zone where bands coalesce into intersecting diamonds undergoes excessive local ovalization causing buckling collapse relatively low overall curvature. simulated finite element model coupled custom constitutive allows for plastic deformation martensitic phase. reproduces moment-end rotation response, evolution diamond shaped patterns. Zones develop such accelerated growth degrades rigidity. In presence small imperfections this degradation evolves buckle in form diffuse negate recoverable property NiTi. Parametric studies show as D/t increases, between becomes stronger making more imperfection sensitive.