Determination of Diameter and Thickness of Weld Nuggets in Resistance Spot Weldings by High Frequency Ultrasound Inspection

摘要

For nondestructive testing of resistance spot weldings several commercial and mobile ultrasonic NDT systems are available. Most of them offer only a very limited C-Scan image resolution. With scanning acoustic microscopy (SAM) it is possible to obtain high-resolution B- and C-Scans and to perform an additional quantitative analysis of HF A-Scans. This allows for a sophisticated analysis of the weld nugget. Therefore, SAM can be used as quantitative reference and calibration tool for commercial testing systems. In the present work the SAM results are compared with a commercial US testing system based on a matrix sensor. In this context a novel spectral evaluation technique with successive image correlation analysis is applied. It is further demonstrated that it is possible to determine not only the lateral dimension (diameter) of the nugget but also its approximate thickness. The latter is obtained by analyzing the effective ultrasound attenuation caused by the interaction with the modified grain structure inside the nugget.