Multiaxial fatigue damage analysis of complex loading paths

Vítor Manuel Rodrigues Anes

Key information

Authors:

Vítor Manuel Rodrigues Anes (Vítor Manuel Rodrigues Anes)

Supervisors:

Luís Filipe Galrão dos Reis (Luís Filipe Galrão dos Reis)

Published in

07/17/2015

Abstract

This thesis proposes a new set of models to improve multiaxial fatigue characterization. The research main objective was to create physical based methodologies to characterize multiaxial fatigue damage under random loading conditions, which is one of the greatest challenges in multiaxial fatigue life assessment. To achieve this goal, five interconnected criteria were developed in this work, namely a cyclic elastic-plastic model, a non-proportional sensitivity parameter, a new equivalent shear stress, a new multiaxial cycle counting method, and a fatigue crack initiation model. Series of fatigue tests were performed to characterize two different materials, i.e. an high-strength steel (42CrMo4) and a magnesium alloy (AZ31B-F), in order to scrutinize their multiaxial fatigue behaviour, including crack initiation planes under proportional and non-proportional loading conditions. Regarding other types of loading such as asynchronous, sequential, variable amplitude, mean stress, and stress gradients, it was used a third-party fatigue data collected from literature. The methods developed here were correlated with state-of-the-art criteria and with experimental data. Based on the achieved results it can be concluded that the proposed methods are easy to implement, easy to understand, and have improved results comparatively to the state-of-the-art criteria.