Torsional Low Cycle Fatigue of Spline-Ended Drive Components

Spline-ended joints of three different kinds of steel materials (9315, 4340, 300 maraging) were tested for torsional low cycle fatigue. The experimental data, the S-N curve fitting and the construction method are presented. The noticeable discrepancies between the actual failure modes and the conventional design criteria for splines are observed. Discussions include allowance for scatter, explanation of a typical failure phenomenon, and an attempt at correlating experimental results with torsional fatigue theory, considering fatigue progression under combined bending and torsion. Some recommendations for an improvement of spline design techniques to predict low cycle torsional strength are proposed, mainly in the categories of spline geometry, material choices, and treatment of stress concentration. A design criteria approach is suggested to account for low cycle torsional fatigue in spline-ended joints