Quantitative metal magnetic memory reliability modeling for welded joints

Metal magnetic memory(MMM) testing has been widely used to detect welded joints. However, load levels, environmental magnetic field, and measurement noises make the MMM data dispersive and bring difficulty to quantitative evaluation. In order to promote the development of quantitative MMM reliability assessment, a new MMM model is presented for welded joints. Steel Q235 welded specimens are tested along the longitudinal and horizontal lines by TSC-2M-8 instrument in the tensile fatigue experiments. The X-ray testing is carried out synchronously to verify the MMM results. It is found that MMM testing can detect the hidden crack earlier than X-ray testing. Moreover, the MMM gradient vector sumKvs is sensitive to the damage degree, especially at early and hidden damage stages. Considering the dispersion of MMM data, theKvs statistical law is investigated, which shows thatKvs obeys Gaussian distribution. SoKvs is the suitable MMM parameter to establish reliability model of welded joints. At last, the original quantitative MMM reliability model is first presented based on the improved stress strength interference theory. It is shown that the reliability degree R gradually decreases with the decreasing of the residual life ratioT, and the maximal error betweenprediction reliability degreeR1and verification reliability degreeR2 is 9.15%. This presented method provides a novel tool of reliability testing and evaluating in practical engineering for welded joints.