Ultrasonic elastography for nondestructive evaluation of dissimilar material joints

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.

Automated summary

The use of dissimilar material joints or multilayered metals is increasing in the manufacturing industry to meet the demand for multifunctional materials. Understanding the mechanical, thermal, or electrical properties of these materials requires investigating lattice mismatch and utilizing techniques like nanoindentation and elastographic mapping. Friction stir welding is an effective method for obtaining dissimilar joints between different metals, and dynamic bulk modulus elastographic mapping provides a non-invasive technique for inspecting bulk metallurgic elastic modulus.