NDT of Weld Joints Using Shearographic Interferometry and Dynamic Exciation 2011-01-0996

Weld Joints are widely used in automotive and aerospace industry. The main issue in the weld joints is the quality inspection to detect the disconnection in the welded area. In this paper, Shearographic technique with dynamic excitation is introduced to test the weld joints. In the experiments, the coupons are of 4 very thin layers of metal sheets welded together. The goal is to find out if there are any disconnections between the layers. They are clamped and then excited by a PZT actuator from behind. A real time digital Shearographic system with a self-refreshed reference image technology has been developed to display the measuring result, i.e. shearogram. A big range of driving frequencies is scanned to find the proper frequency and amplitude that can help to identify the disconnections.

The results show that when the driving frequency reaches the resonance frequency, there will be big amplitude and thus a fringe pattern becomes visible on the coupon surface. If the weld joints area is perfect, the resonance frequency in the weld joint area is very high, and no resonance frequency will be found in the weld joint area except for extremely high frequency. Instead if the welding is disconnected, a resonance with low frequency in the area of the weld joint can be found and a fringe pattern in the joint area can be found, that means the disconnection can be identified immediately. On the other hand, if the driving frequency reaches the resonance frequency of the base plate, the coupon surface will be full of fringes and these frequencies are not suitable for the detection. This paper presents a methodology of this developed laser shearography for NDT of weld joints using dymanic excitation. The experiments show the feasibility of detecting the defect in the weld joints by using Shearography system and if the frequency is chosen properly, the result is clear and reliable.