Magnetic means for determining torsional yield strength

The presence of a unique residual stress distribution at zero applied torque, in shafts that have been previously subjected to torque levels high enough to cause yielding, is made apparent by readily detected helical magnetic anisotropy in the surface regions. Following application of ever higher torques, and upon relaxation to zero torque, consecutive current pulses of respectively opposite polarity are conducted axially through the sample shaft. The appearance and rapidly rising values of integrated EMFs induced in a small encircling search coil signifies the presence of axial components in the remanent magnetization being reversed by the circumferential field of the current.