Tension-tension fatigue experiments of demagnetized notched specimens made of middle-carbon 45 steel were conducted,and off-line magnetic signal characteristics in the stress concentration zone under different numbers of cycles were investigated using magnetic memory testing instrument simultaneously.The results show that an abnormal wave occurs in the notch position due to the leakage magnetic field caused by discontinuous geometric shape before loading,and may reverse after loading.The magnetic signal curves hardly change after the specimen is loaded in some specific number of cycles,and the wave heights in the notch increase with increasing cycle in the last stage until there is a sharp increase when the specimen fractured.Maximum magnetic field gradients of magnetic signals induced only by stress concentration were extracted by eliminating the disturbance of two clamps made of steel,and the fatigue procedure can be divided into four stages,which reflect different damage degree in the stress concentration zone.The experimentally measured damage values expressed by characteristic quantity of magnetic signal coincide with theoretically calculated fatigue damage evolution law,early predicting the residual fatigue lifetime.
Key words
fatigue damage /
magnetic memory technique /
stress concentration /
abnormal wave /
magnetic field gradient
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