Abstract
Stress corrosion cracking (SCC) widely occurs in the key structures of large-scale mechanical systems and may cause catastrophic accidents without evident macroscopic deformation. A sufficiently accurate quantitative evaluation of SCC is important to guarantee the safety and efficient operation of large mechanical systems. However, the reconstruction accuracy of SCC shape parameters using eddy current testing (ECT) signals remains a problem, given the complex microstructure of cracks and the properties of the ECT inverse problem. In this study, a two-dimensional numerical model of crack with conductivity distribution is used to calculate the ECT signals due to SCC. The relation between crack parameters and ECT signals is investigated through simulation and experiment. Results show that the ill-posedness of SCC shape reconstruction is mainly manifested in the nonuniqueness of the solution of crack shape parameters. Therefore, a regularization method based on the features of multifrequency ECT signals is proposed to solve ill-posedness by adding prior information to the solution space of the optimization problem. The reconstruction results of the simulated and measured ECT signals from the conductive crack models verify that the proposed strategy can effectively improve the precision of SCC shape reconstruction.
Highlights
Stress corrosion cracking (SCC) is a delayed fracture phenomenon that often occurs in some metal materials due to the combined effect of tensile stress including residual stress and a corrosive environment
This study reveals that the ill-posedness of SCC shape reconstruction using single-frequency eddy current testing (ECT) signals is mainly manifested in having multiple local optimal solutions when the predicted signals are close to the measurement results
By using the relationship between the parameters of SCC and the features of multifrequency ECT signals, an SCC shape parameter reconstruction scheme based on a regularization method is proposed
Summary
Stress corrosion cracking (SCC) is a delayed fracture phenomenon that often occurs in some metal materials due to the combined effect of tensile stress including residual stress and a corrosive environment. For complex natural cracks, such as SCC, the predicted shape parameters of cracks may be far away from the true values even when the calculated ECT signals are close to the measurements for signals of single-frequency excitation. The information of single-frequency ECT signals is not enough to determine the true solution of SCC shape parameters. To overcome this problem, several numerical criteria are usually added to the solution space in practical work, thereby identifying a reasonable solution in a certain range or sense. A regularization method using multifrequency ECT signals is proposed to determine the crack parameters gradually at different depths and obtain a solution close to the true value
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