Failure analysis of NiTi wires used in medical applications
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Superelastic nitinol (NiTi) wires have been fractured under various loading, temperature, and environmental conditions. The fracture surfaces of these NiTi specimens were then characterized using scanning electron microscopy (SEM) to provide a reference for future NiTi failure analysis investigations and to provide comparison with the existing literature. The results of this study indicate that NiTi fracture modes and morphologies are generally consistent with those for ductile metals, such as austenitic stainless steel, with one important exception: NiTi exhibits a unique compressive damage mechanism that occurs at high strains in bending. Compression-induced surface damage is observed at the compression-side of tight bends or kinks in NiTi wire. In these same samples, no cracking or surface damage is observed on the tensile side of the bend. Compressive damage begins as slip line formation due to plastic deformation, and at high strain levels, cracking is observed. These compression-damage induced cracks appear to initiate from slip lines and extend in a mode II/shear mechanism.
Keywordscompressive damage failure analysis fracture nitinol
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