Piezomagnetic Behavior Corresponding to the Variations of the Toughness of X70 Steel Under Cyclic Loadings

The goal of this study is to investigate magnetic field characteristics corresponding to variations of the toughness of X70 pipeline steel under cyclic loading. After a series of stress-controlled cyclic loadings, the specimens were subjected to static tensile tests. Changes in the magnetic field were recorded simultaneously during the test. The results suggest that cyclic loadings will reduce the toughness of the material. The initial value and slope of the magnetic field-strain curve obtained in the static tensile test are related to the number of cyclic loadings. The evolutions of magnetic field and the stress-strain curve can reflect variations in the toughness of materials. Compared with the stress-strain curve, the magnetic field demonstrates the fatigue degradation process more markedly. The high sensitivity of the magnetic field to toughness may be used to estimate the degree of fatigue damage of steel.