Issue 28

B. Ye et alii, Frattura ed Integrità Strutturale, 28 (2014) 32-41; DOI: 10.3221/IGF-ESIS.28.04 32 Quantitative estimating size of deep defects in multi-layered structures from eddy current NDT signals using improved ant colony algorithm BoYe,MingLi, Gefei Qiu, JunDong, FangZeng Faculty of Electric Power Engineering, KunmingUniversity of Science andTechnology yeripple@hotmail.com , kingttlly@foxmail.com , tsugefei@foxmail.com , yn_dj@tom.com fanger1119@163.com TanghuaYang, BiaoBai Puer power supply bureau, Yunnan PowerGridCorporation aiyi2001@sina.com , baibiao2014@hotmail.com A BSTRACT . Detection and quantitative estimation of deep defects inmulti-layered structures is an essential task in a range of technological applications, such as maintaining the integrity of structures, enhancing the safety of aging aircraft, and assuring the quality of products. Anovel approach to accurately quantify the two-dimensional axisymmetric deep defect size from eddy current nondestructive testing (NDT) signals is presented here. The method uses a finite element forward model to simulate the underlying physical process and an improved ant colony algorithm (IACA) to solve the inverse problem. Experiments are carried out. The performance comparison between the IACA method and the least square method is shown. The comparison results demonstrate the feasibility and validity of the IACAmethod. Between them, the IACAmethod gives a better estimationperformance than the least squaremethod at present. K EYWORDS . Eddy current nondestructive testing; Finite element method; Ant colony algorithm; Multi-layered structures; Defectmeasurement. I NTRODUCTION ulti-layered structures are widely used in many different structural systems, such as nuclear structures, composite aircraft structures, and other civil engineering structures [1]. Structural integrity is one of the prime requirements for multi-layered structures in working condition. The continuous operation of multi-layered structures leads to the loss of its material due to defect generation [2, 3]. The generation of defects in the structure does not mean that structure is at the end of its service life; it becomes necessary to check themulti-layered structure integrity to ensure optimal utilization to its service life. To check themulti-layered structures, various nondestructive testing (NDT) techniques are used, such as visual inspection, eddy current (EC) technique, ultrasonic technique, X-rays, etc. Among these NDT techniques, the eddy current nondestructive testing (ECNDT) method is a useful technique for detecting defects in conductive materials, especially in multi-layered structures. When using the other NDT techniques [4-8], it is widely recognized as being both a complex and critical problem. M