Fatigue behavior analysis of blade incidence angle flight link rods

Abstract

The significance of this thesis lies in the application of the XFEM method to the fatigue analysis of a helicopter's main rotor pitch links, which are responsible for transmitting motion from the swashplate to the blade. This research combines both experimental and numerical methods to systematically investigate the defect-position and size study validated by experiments on AISI 1045 steel on the pitch links. We conducted tensile and fatigue tests on specimens made of AISI 1045 steel to provide data for validating the numerical model. Furthermore, we used a three-dimensional finite element method in ABAQUS to evaluate residual stresses and deformations, and finally, we determined the SIF by applying XFEM to a fatigue crack in the rod. The variation of SIF with crack length enabled the prediction of fatigue life based on Paris's law. At the beginning of this work, we performed a heat treatment, finding that tempering is crucial for improving the mechanical properties of AISI 1045 steel by relieving internal stresses. While tempering at 350 °C yields the optimum tensile strength (approximately 1490 MPa), using higher temperatures, up to 550 °C, significantly reduces this strength (by up to 36\%). In the second part, the results successfully confirmed the accuracy of the numerical model in simulating the experimental stress-strain curve. Fatigue tests showed that XFEM effectively matched numerical predictions, highlighting the influence of stress state and cyclic load levels on fatigue life. Crack position and depth were linked to the number of cycles to failure and SIF variations. Following this study, the AISI 1045 steel model was deemed suitable for a helicopter main rotor control rod