Abstract
Mechanical properties of NiTi shape memory alloy (SMA) were obtained using uniaxial tensile testing and dog-bone specimens. Critical crack tip opening displacement (CTOD) was measured at room temperature on compact tension (CT) specimens using experimental methods of elastic-plastic fracture mechanics (EPFM). To observe the effect of martensitic phase transformation on CTOD, tests were also carried out above martensite deformation temperature (Md). To obtain the displacement and strain fields around the crack tip, under Mode-I loading, digital image correlation (DIC) was used. The extent of transformation zone was calculated using the measured strain field. Finite element analyses were carried out to solve the 2D CT specimen problem under Mode-I loading. Critical CTOD values were calculated for both superelastic and austenitic NiTi for comparison purposes. Size of the transformation zone at the crack tip was also calculated together with crack face opening displacement. The computational and experimental results were compared and discussed. CTOD measurements showed that the phase transformation ahead of the crack tip, improves the fracture behavior of NiTi.
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