Metal Magnetic Memory Testing Signals Response to Alternating Stress during On-line Measurement of Ferromagnetic Steel
摘要
Metal magnetic memory testing (MMMT) has attracted considerable interest for its capability in stress concentration evaluation. An experimental investigation of the response of MMMT signals to the alternating stress in a single tension–compression stress cycle was carried out in Q235 steel. The normal component of the MMMT signals, Bz was an inclined line throughout the test and the tangential component of the MMMT signals, Bx was horizontal. The slope of Bz, KBz, and the mean value of Bx, Bxave, were extracted and the variation behaviour was presented and analyzed. During the tensile loading stage, KBz and Bxave initially increased with the applied stress, and then decreased. During the tensile unloading stage, KBz and Bxave did not change in the original manner, but continued to increase, and then decreased when the stress was completely released. KBz and Bxave kept decreasing during the compressive loading stage. While KBz and Bxave continued to increase throughout the compressive unloading stage, and they were smaller than those when the applied stress was the same during the compressive loading stage. When the compressive stress was completely unloaded, KBz and Bxave were slightly larger than when the tensile stress was completely unloaded. The results indicate that in on-line MMMT for stress evaluation, the stress state for each measurement (i.e., the applied stress that the workpiece was subjected to when performing MMMT) should be consistent to ensure the accuracy of stress evaluation.