THE EFFECT OF UNIAXIAL RATCHETING ON PIEZOMAGNETIC RESPONSE OF X80 PIPELINE STEEL CONSIDERING LOADING HISTORY

摘要

The objective of this research is to investigate the effect of uniaxial ratcheting on the piezomagnetic field variations of X80 pipeline steel where the loading history is a major consideration. The piezomagnetic field variations of initially undemagnetized X80 pipeline steel specimen were recorded simultaneously by an APS 428D fluxgate magnetometer during the whole asymmetrical cyclic stressing process. The variations of the ratcheting strain and its rate with the changing mean stress were obtained. The influence of the loading history on the uniaxial ratcheting behavior was investigated. It was found that the prior loading step with higher mean stress greatly restrains the ratcheting behavior of subsequent loading step with lower mean stress. On the contrary, the prior loading step with lower mean stress does not play a significant role on the subsequent ratcheting behavior. The corresponding variations of the piezomagnetic hysteresis curve with the uniaxial ratcheting proceeding were systematically studied in terms of its shape and position, and the underlying reasons were discussed based on the magnetic domain theory and the dislocation theory.