Stress dependence of the magnetic properties of steels
It is well known that the magnetic properties of ferromagnetic materials are sensitive to microstructural and mechanical changes. Variations in applied stress, composition, and geomrtry will, either alone or in combination with each other, cause the magnetization process to change. The primary way to monitor changes in the magnetization process is to run the material or component of interest through a hysteresis cycle and plot the magnetic response on the B,H (magnetic induction, magnetic field) plane. The result is a hysteresis loop, a typical example of which is given in Figure 1.1. The figure also shows a number of parameters that are used to describe the hysteresis loop. The coercivity (Hc) ~s the magnetic field value as the induction passes through zero. The remanence (Br) is the induction value as the magnetic field passes through zero. The maximum differential permeability (μ'max) is the slope of the loop as it passes through the coercivity. The hysteresis loss (Wb) is the area enclosed by the loop. The initial differential permeability (μ'in) is the slope of the curve just at the start of magnetization from the demagnetized condition. The maximum or saturation induction (Bmax) is the largest induction value.