Investigation of the Axial and Torsional Low-Cycle Fatigue Properties of Notched High Strength Steels for Application to Landing Gear Fuse Pins

Abstract

Accurate and reliable fuse pin fatigue life estimates are a priority for public safety; however, development of a comprehensive parametric model remains a significant engineering challenge. This work assessed the usage of parametric uniaxial strain life models for multiaxial life prediction induced by notches for application to fuse pins. AISI 4340 and 300M steel coupons were tested under pure axial and pure torsional loading with fully-reversed, mean stress, and residual stress conditions. Residual stresses had a negligible effect on axial and torsional fatigue lives due to stress relaxation, while mean stresses either quadrupled (compressive) or at least halved (tensile/torsional) fatigue life.The strain life prediction model effectively predicted axial fatigue lives, although results were sensitive to the fatigue ductility exponent. Shear strain life models were nonconservative for predicting low-cycle fatigue life in torsion. Future work should consider scale and environmental effects when applying these findings to fuse pin fatigue design.