Fatigue damage evaluation by metal magnetic memory testing

WANG Hui-peng(王慧鹏), DONG Li-hong(董丽虹), DONG Shi-yun(董世运), XU Bin-shi(徐滨士)

(National Key Laboratory for Remanufacturing, Academy of Armored Forces Engineering, Beijing 100072, China)

Abstract:Tension-compression fatigue test was performed on 0.45% C steel specimens. Normal and tangential components of magnetic memory testing signals, H_p(y) and H_p(x) signals, with their characteristics, K of H_p(y) and H_p(x)_M of H_p(x), throughout the fatigue process were presented and analyzed. Abnormal peaks of H_p(y) and peak of H_p(x) reversed after loading; H_p(y) curves rotated clockwise and H_p(x) curves elevated significantly with the increase of fatigue cycle number at the first a few fatigue cycles, both H_p(y) and H_p(x) curves were stable after that, the amplitude of abnormal peaks of H_p(y) and peak value of H_p(x) increased more quickly after fatigue crack initiation. Abnormal peaks of H_p(y) and peak of H_p(x) at the notch reversed again after failure. The characteristics were found to exhibit consistent tendency in the whole fatigue life and behave differently in different stages of fatigue. In initial and crack developing stages, the characteristics increased significantly due to dislocations increase and crack propagation, respectively. In stable stage, the characteristics remained constant as a result of dislocation blocking, K value ranged from 20 to 30 A/(m·mm)^-1, and H_p(x)_M ranged from 270 to 300 A/m under the test parameters in this work. After failure, both abnormal peaks of H_p(y) and peak of H_p(x) reversed, K value was 133 A/(m·mm)^-1 and H_p(x)_M was -640 A/m. The results indicate that the characteristics of H_p(y) and H_p(x) signals were related to the accumulation of fatigue, so it is feasible and applicable to monitor fatigue damage of ferromagnetic components using metal magnetic memory testing (MMMT).

Key words:metal magnetic memory testing; MMMT signal; tension-compression fatigue test; feature extraction