Ultrasonic elastography for nondestructive evaluation of dissimilar material joints

[Display omitted] •We applied new dynamic bulk modulus elastography on friction stir welding workpiece.•This technique enables the evaluation of the dynamic mechanical property to locate the elasticity mismatched region.•The determined elasticity mismatch can be further applied for predicting the extent of stress concentration under various loading conditions.•The matrix of these two materials (Fe and Cu) is metallurgically immiscible to exclude the presence of brittle reaction products.•The predicted stress concentration region from elastography agreed with the mechanical test results. Dissimilar material joints or multilayered metals have become inevitable in the manufacturing industry due to the increasing demand for multifunctional materials with variable mechanical, thermal, or electrical characteristics in a single assembly. Lattice mismatch of materials at the interface of dissimilar materials leads to inferior mechanical characteristics. In particular, the mismatch in elastic properties indicated by a large initial elastic deformation is critical to determine the extent of variation in stress. However, nanoindentation, the most common and accepted technique to measure elastic modulus, is destructive, time-consuming, and can only examine mechanical properties within a limited area. A non-invasive elastographic mapping technique evaluates the mechanical properties using ultrasonic elastography to study incompressibility. The dissimilar joint between steel and copper was obtained via friction stir welding. The variation of the stress developed at the welded joint of the two different metals was evaluated from the dynamic bulk modulus map. A tensile test of the involved workpiece confirmed a good agreement with our analysis based on the dynamic bulk modulus elastographic mapping results. This study provides a rapid and non-invasive technique for the bulk metallurgic elastic modulus inspection to overcome the limitations of conventional methods.