Nondestructive ultrasonic inspection of friction stir welds

Friction Stir Welding (FSW) is a relatively new solid state welding procedure developed at The Welding Institute (TWI-UK) and is widely considered for welding aluminum alloys in various applications. In order to inspect the quality of the welds and to detect a variety of welding flaws such as wormholes, Lack of Fusion (LOF) and Lack of Penetration (LOP) defects, it is required to develop a methodical examination technique that can be used for the identification and the localization of all such defects. The most prevalent and risky defect in this type of welding is the unrevealed lack of penetration (also known as the root flaw with a length varying from 100-700 µm). Due to the characteristics of the flaw, conventional ultrasonic methods are not always able to readily detect such fine Lack of Penetration (LOP) defects. Here, we propose a novel approach to characterize root flaws using an oblique incident ultrasonic C-scan backscattering analysis. The implementation consists of an immersion ultrasonic testing method in pulse echo (i.e. backscatter) mode with a 3.5 MHz transducer, and makes use of an empirical method to allow focusing and gating the received signal for root flaw examination. By scanning the surface above the welded component, a “slanted C-scan” image, displaying the backscattering response from the root surface of the nugget zone, can be obtained which allows a simple interpretation of the root flaw status of the weld.

Jaar van publicatie:2015

BOF-keylabel:ja

IOF-keylabel:ja

Authors from:Higher Education