In-situ measurement of tensile deformation-induced magnetic fields in high strength low alloy steels using GMR based metal magnetic memory technique

Abstract

This paper presents in-situ measurement of tensile deformation-induced self magnetic leakage fields (SMLFs) in high strength low alloy (HSLA) steel specimens (200 mm length, 20 mm width and 4 mm thick) using giant magneto-resistive (GMR) sensor based metal magnetic memory (MMM) technique. SMLFs were measured during the tensile loading for six different pre-defined loads viz. 188, 376, 412, 451, 470 MPa and load upto failure using five GMR sensors kept at different locations of the specimen. 3D-nonlinear finite element (FE) modeling was performed to correlate the stress-strain state in the specimen with the experimental SMLF signals. Studies reveal that the SMLF signals are different for the different loads as well as locations of GMRs. Among the five GMR sensors, the GMR 1 (located at the grip region) and GMR 2 (located near the region of reduced cross-section) show no significant changes with the stress / strain for all the elastic, plastic and failure loads. The GMR 3, GMR 4 and GMR 5 (located at or near the center of gauge length) show initial increase and decrease during elastic load, increase during plastic load and then, decrease after necking during failure load. The variation of GMRs output is found to be more pronounced during the plastic load, as compared to variations during elastic and failure loads. The variation of GMRs output during the tensile deformation also shows a good correlation with the stress-strain state measured experimentally as well as FE model predictions.