Application Of A Double Linear Damage Rule To Cumulative Fatigue PDF Download

Fatigue failure is one of the most common type of failures when a load bearing component or structure is subjected to constant or variable amplitude cyclic loading. Material fatigue behavior under a given variable amplitude loading program could be evaluated both experimentally (fatigue testing) and analytically (cumulative fatigue damage rules). As fatigue testing is often a costly and time consuming method, cumulative fatigue damage models are commonly used for fatigue life prediction analysis. The main objective of this study was to investigate applicability of the commonly used Linear Damage Rule (LDR) for cumulative fatigue damage analysis of metallic materials with different cyclic softening/hardening deformation behaviors. LDR and five non-linear cumulative damage models were employed to predict fatigue life of several variable amplitude loading histories without presence of mean stress. These models were implemented in conjunction with conventional fatigue-life curves (strain-life and stress-life curves). In addition, LDR was also applied with SWT-life curve (a parameter which includes both strain and stress values of loading events). For the purpose of cumulative fatigue damage analysis, variable amplitude loading experimental results (in form of step loading, periodic overloading and block loading) of 16 metallic materials were used from the literature. For the materials with strong cyclic deformation behavior, it is shown that LDR with SWT approach leads to similar or even more accurate fatigue life predictions than any of the studied non-linear damage models. However, for the materials without considerable amount of cyclic hardening or softening, non-linear damage models performed relatively better than LDR with either SWT approach or conventional approach. Moreover, fatigue properties of materials fabricated with Selective Laser Melting (SLM) and Electron Beam Melting (EBM) processes (two common AM processes) were also reviewed based on fatigue data from the literature. To apply cumulative fatigue damage models for these materials, some recommendations are made based on the performance of cumulative fatigue damage models for the traditional-fabricated metallic materials. However, the accuracy of the proposed approach needs to be validated by variable amplitude loading experimental results, which are not currently available in the literature or in the open access databases.