Estimation of Fatigue Life Components By Proposed Mathematical Model

Abstract

In this study the fatigue behavior of an aluminum alloy designated 2024 – T3under constant and variable amplitude of stresses is considered. The applied loadadopted is a rotating bending one, the cross Section of the laboratory samples iscircular with a diameter of (6.74mm). All tests were carried out under a stress ratioof R = - 1 and at room temperature condition. The study consists of two partsexperimental and theoretical. The experimental part includes carrying outlaboratory tests on two groups of specimens the first group was tested underconstant stress amplitude to establish the S-N curve of the specimen's material,while the second group was tested under variable amplitude of stress to assess theeffects of the accumulated fatigue damage. The theoretical part of the studyincludes a review of previous literature adopted to derive a theoretical andmathematical model depending upon the variation of the stresses obtainedbysome previous theories, taking into consideration low and high stress levels, andeven post yield.The derived model is denoted as elastic-plastic model for the evaluation of lifetime of machinery parts. The linear theory of Miner and the theory of ElasticCracks Propagation are also studied throughout the theoretical part of the study.In order to assess the capability of the two theories with the derived model: acomparison is held between the experimented results and the results obtained byapplying the two theories.It is noted that results obtained by applying the two theories are lower(underestimates) than those obtained from the experimental study and that resultsobtained by the suggested derived model are in better agreement than thoseobtained by the two theories.