Characterization Of Nitinol Weld Joints By Nondestructive Testing

Joining technology is important for laser-cut Nitinol implants as well as for wire-based devices. Besides crimping and riveting processes especially laser-welding technologies are applied. In addition to connecting wire ends the laser-welding process is used for joining Nitinol components even with different materials like stainless steel.

Up to now the testing of such joinings is mainly carried out destructively by tensile tests which can only be performed on a sampling base. However, for a reliable hundred-percent testing a nondestructive testing (NDT) method is needed. For the partially very small joining areas and low profiles of the welding area this task is very challenging.

In this study laser-welded joints with different dimensions and manufactured with various laser parameters were characterized by a nondestructive heat flow analysis based on an intensity-modulated laser excitation. This test method was chosen because of the high responsivity and good resolution. The evaluation was performed according to phase angle response. Results were compared with x-ray tomography and destructive torsional tests, where the maximum torque at fracture was measured.

The presentation highlights the latest developments in nondestructive characterization of weld joins and a nondestructive evaluation of laser-welding quality from a technical point of view.