EFFECTS OF STRESS ON THE PROBABILITY OF DETECTION FOR MAGNETIC FLUX LEAKAGE INSPECTION

摘要

This paper presents a scheme for calculating the POD of a flaw with respect to stress in the sample. A structural analysis ANSYS FE model was first used to generate the stress distribution, obtained in the presence of an external load and after removing the load. The stress levels in each element were mapped to a B -H curve, using functional interpolation. A magnetic FE model was used to simulate the MFL inspection signals. Function fitting was used to establish the relationship between stress and peak of the MFL signal. The conditional pdfs of the flaw and background signals were obtained by randomly perturbing the stress parameter in the functional relationship between stress and the peak of the MFL signal. The use of function fitting reduced the number of FE simulations necessary to compute the pdfs. Furthermore, this reduction did not compromise the accuracy of the results. It was found, that the presence of residual stresses does not affect the detectability of flaw A, when measured under optimal conditions. However, the presence of large "active" stresses can render flaw A impossible to detect, even when measured under optimal conditions, which is mainly due to the fact that the active stresses surrounding the defect are mainly compressive in nature.