Proposition of dog-bone geometry for shape memory alloys under simple tensile test

In the present work, simple tensile test of shape memory alloys (SMAs) is studied by considering stress concentration caused by the grippers. In order to simulate SMA behaviors in this test, finite element method is employed to obtain pre-stress distribution along the specimen due to fastening the grippers prior to the application of tension. Then Brinson's ۱-D constitutive model is used to study transformations during the tensile loading-unloading. It is found that the pre-stress leads to a non-uniform distribution of uniaxial stress as well as martensite volume fraction throughout a wire. Therefore, the so-called dog-bone geometry is suggested and optimum dimensions are proposed to obtain a uniform tensile stress distribution when testing an SMA specimen. This gives rise to a nearly simultaneous transformation along the whole specimen. The optimum dimensions are shown to be different from those reported by ASTM.

Keywords:

simple tensile test , shape memory alloy , dog-bone , pre-stress , finite element