V. L. Richards, H. Phukan, University of Missouri – Rolla, Rolla, MO; R. Talwar, R. J. Lederich, D. R. Bolser, Advanced Manufacturing R&D, Boeing – Phantom Works, St. Louis, MO; D. L. Ballard, Air Force Research Laboratory, Wright-Patterson AFB, OH

Summary:

The two most common defects in friction stir welded butt joins are Lack of Penetration (LOP) and Advancing Side wormhole. Both of these defects result from inadequate material transportation or deformation. Detectability of these two types of defects, particularly the former, has been difficult using conventional NDE methods. Since the LOP or disbond is not a volumetric defect, it is not detectable by radiographic methods or conventional ultrasonic testing.

As observed from existing literature, Phased Array Ultrasonic methods have been tried for detecting LOP defects, but are not fully successful. This paper examines another method of detection of friction stir welding defects via Eddy Current method. Tests were carried out on post-processed butt welds in 2024 aluminum alloys plates. Variation of phase angle and voltage vector magnitude was observed as functions of distance from start of the weld. Variation of phase angle as a function of weld pitch (quasi-thermal parameter) and preset gap or shim thickness, has been studied, and a correlation has been shown. Simultaneously, the discontinuities were characterized by examining the cut up sections of welds of different process parameters. Accordingly a table showing the maximum and minimum dimensions of the discontinuities detected was documented. The authors gratefully acknowledge the support of the Air Force Research Laboratory through contract no. FA8650-04-C-704 (Dr. Jaimie S. Tiley, Program Manager).