STRESS STATE IN THE COMBINED STRESS TORSION TEST

An analysis of the stresses in the axial stress-torsion test is presented by considering the gage section as a cylinder undergoing uniform axial deformation with superimposed torsion. Calculation of the stresses requires measurement of the radial deformation and penetration of the plastic region into the notch shoulders. The hydrostatic stress exhibits a peak within the wall of the gage section which increases with decreasing gage length. The fracture strain in room temperature tests increases with decreasing gage length when a compressive axial load is applied and decreases slightly with decreasing gage length when a tensile axial load is applied. Severe distortion and large changes in length of the gage section during hot torsion testing prevent application of the analysis to high temperature tests.