Effect of uniaxial stress on the reversible and irreversible permeabilities of 2% Mn pipeline steel

The results of a study of the effects of constant uniaxial stress on the irreversible and reversible differential permeabilities of minor and saturation major hystersis loops are presented, extending an earlier study which studied those permeability components on the initial magnetization curve. Tension was found to increase both the reversible and irreversible components of the saturation major loop differential permeability in the low magnetization region, and to decrease them in the high magnetization region. The opposite effect was found for compression. This effect was explained as the result of changes in the domain structure of the sample when stressed and a resulting change in the ratio of 90° of 180° domain walls. The differences between the upper and lower branches of the saturation major hysteresis loop reversible relative differential permeability were found to increase in tension and decrease in compression, with more complicated behavior occurring in the irreversible component. Minor loop behavior was also found to vary depending on the magnetization of the sample. In the low magnetization region tension was found to produce higher values and larger variations in both components of the relative differential permeability than the unstressed case, while compression produced lower values and smaller variations. The opposite behavior was found to be true in the high magnetization region, while an intermediate behavior with little or no change in both the relative differential permeability components was found to exist between the two extreme cases. The minor loops were measured from set values of the applied field, and tension was found to increase the corresponding values of magnetization, with compression causing a decrease in the magnetization values. The behavior of the minor loops was found to be related to the major loop behavior in the same region