Theoretical consideration on the fracture of shape memory Alloys

The application of shape memory alloys (SMA), as an advanced material, has accelerated in recent years, especially in biomechanical engineering. However, there is a lack of understanding of the fracture behavior of SMA devices. This paper presents our consideration on the theoretical study of the fracture properties of SMA. Owing to the existence of a new transformed phase near the crack-tip region, the transformation strain, including the transformation volume strain and the shear strain, the plastic deformation, and the mismatch of elastic property will alter the crack-tip stress field and hence govern the fracture behavior of the SMA material. Therefore, it is vital to clarify the influence of these factors on the fracture toughness. Following this consideration, the paper reports our recent research progress in this direction. First, a simple study is carried out to show the influence of transformation consisting of pure volume contraction. These results reveal that the phase transformation with volume contraction in SMA tends to reduce their fracture resistance and increase the brittleness. Second, a constitutive model is established to quantify the effect of stabilization of plasticity on the stress-induced martensitic trans-formation. Third, the effect of transformation strain with shear and volume components on the fracture toughness of a superelastic SMA is studied.