Effect of deformation on crack extension measurement for compact tension specimen with the DCPD technique

Abstract

Direct current potential drop (DCPD) technique is a crack growth monitoring technique widely used in the crack growth test of specimens in laboratory environment. Deformation of the specimen during test is one of the important factors that affect the accuracy and resolution. Because the effect of deformation on measurement is usually mixed with other factors, quantitative evaluation is difficult through experiments method only. In this work a novel quantitative estimation method combining experiment and finite element analysis has been proposed, and the effect of deformation on measurement for 316 L stainless steel compact tension specimen has been quantitatively evaluated. Through the tensile test and DCPD monitoring test of the non-cracked 316 L stainless steel plate-shaped specimen, the material mechanical property parameters and the change of potential drop caused by deformation were obtained. Then the slow tensile tests have been performed on compact tension specimens. Combined with the FE simulation of the experimental process, the effect of deformation on the potential drop under different crack length has been evaluated. The results show that the influence of deformation on the potential drop is a factor that must be considered for the crack growth monitoring experiment with high crack growth resolution. The proposed method can be used to quantitatively evaluate the influence of deformation, a factor that was usually ignored in the past, on the measurement of crack growth, which provides a method and basis for correction of crack measurement errors caused by deformation. In addition, the proposed method can be used to obtain a more accurate calibration function, which is of great significance to the improvement of the accuracy and resolution of crack growth monitoring.