Fatigue Life Prediction and Experimental Study of Landing Gear Components via FKM Local Stress Approach

Abstract

This study focuses on high-cycle fatigue (HCF) of aircraft landing gear (LG) components, covering material testing, full-scale component experiments, finite element (FE) modeling, life-prediction comparison, and probabilistic assessment. Fully reversed axial fatigue tests on forty 300M steel specimens were conducted to establish a reliable S-N curve. Full-scale fatigue experiment conducted on the upper torque link components showed that the one cracking at approximately 184,000 cycles (at the filet), while another remained undamaged after 166,000 cycles, providing a benchmark for model validation. FE simulations using ANSYS accurately captured the stress field within the component, with a maximum error of less than 10% compared to experimental strain measurements. Based on the FKM guideline, this work developed an improved FKM local-stress approach (LSA) for HCF life prediction, which integrates load-dependent stress gradients, FKM mean stress correction, and interpolated surface-condition factors for S-N curve adjustment specific to the component’s surface treatment. It predicts the fatigue life as 174,000 cycles (−5.4% error relative to test), outperforming standard FKM-LSA calculations and nCode software simulations. Furthermore, by augmenting the experimental data and constructing p-S-N curves, the improved LSA was extended to predict fatigue life under different survival probabilities and confidence levels, providing a practical tool for reliability-based design.