High Strain Torsion Fatigue of Solid and Tubular Specimens

A stress-strain history theory is developed for the entire life of solid cylinders subjected to reversals of torque under low-endurance fatigue conditions. Thin tubes and solid cylinders of a hot rolled mild steel are found to have identical stress range versus strain range relationships. However, fatigue behaviour is dependent on the stress field surrounding the crack initiation zone and hence the geometry of specimens has a most important effect in high strain fatigue processes. Cold drawn mild steel tubes that have an internal to outside diameter ratio in excess of 0.5 have reduced lives because of the absence of the constraining, less highly stressed core.