A novel method for quality control of post weld heat treatment process using modal parameters

Structures are commonly assembled by welding and they contain residual stresses. Therefore, in many cases, post weld heat treatment is a must to reduce residual stresses. In this research a new NDT method is introduced which can be performed very fast by low cost devices and with almost no running cost. The change in natural frequencies and corresponding mode shapes is introduced as a new NDT method. The proposed method based on comparison of modal parameters, evaluates the amount of residual stress in the structure. The experimental setups are welded plates which are post weld heat treated (PWHT) at different temperatures. These temperatures are specifically chosen to relief some of the residual stress. The level of residual stress could be detected by studying and comparing the identified natural frequencies and mode shapes. This method could be applied successfully in industries where the general requirement of modal analysis i.e. tolerable noise and excitation source are prepared. In comparison to other conventional NDT methods, performing and interpreting results of this method is simple and less complicate which could be easily conducted by NDT technician.