Defect depth retrieval method based on nonlinear transformation for pulsed thermographic inspection

Abstract

The carbon fiber reinforced polymer (CFRP) has been widely used in the aerospace field. During its utilization under the severe environment, CFRP is prone to defects, including impacts, debonds, delaminations, and cracks. Optical pulsed thermography (OPT) nondestructive testing has been used for qualitative and quantitative analysis of such defects. This paper proposes the nonlinear transfer model of peak contrast time analysis to determine defect depth by using OPT technology. The mechanism of the nonlinear relationship between peak contrast time and defect depth is demonstrated and validated by experiments. To effectively predict the defect depth, gaussianization transform is modeled as a nonlinear conversion in defects depth determination. The results of the experiments have indicated that the proposed method has significantly enhanced the accuracy in depth determination.