Pulse-modulation Eddy Current Imaging and Evaluation of Hidden Flaws in Layered Conductors

Layered conductors are widely adopted in critical structures of the engineering fields including aerospace, energy, chemical, etc. Due to the harsh environment, they are prone to such hidden flaws as wallthinning defects (WTD) which conceal themselves particularly at the interfaces between layers, and undermine the mechanical strength as well as integrity of engineering structures. This makes it imperative to detect and evaluate hidden WTD via effective nondestructive evaluation (NDE) methods. Pulse-modulation eddy current (PMEC) has been found to be superior to other NDE techniques in detection, imaging and assessment of back-surface flaws in conductive slabs. It could be one of the promising methods for evaluation of hidden WTD in layered conductors. In this paper, an analytical model of PMEC inspection of hidden WTD is established. Following the theoretical simulations based on the model, the excitation parameters of PMEC especially the carrier frequency are sought. Together with the optimal excitation parameters determined, a testing system of PMEC imaging and evaluation of hidden WTD is built up. The experimental results along with the simulations indicate the feasibility of PMEC for high-sensitivity detection and high-accuracy evaluation of hidden WTD in layered conductors.