An Integral Formulation of Two-Parameter Fatigue Crack Growth Model

Jianguo Wu,Shan Jiang,Wei Zhang,Zili Wang

doi:10.1155/2018/8707929

Jianguo Wu, Shan Jiang + Show 2 more

Open Access

https://doi.org/10.1155/2018/8707929

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Abstract

A two-parameter fatigue crack growth algorithm in integral form is proposed, which can describe the continuous crack growth process over the time period. In this model, the fatigue crack propagation behavior is governed by the temporal crack-tip state including the current applied load and the physical condition due to the previous load sequence. The plasticity-induced crack closure, left by the historical loading sequence, controls the following fatigue crack growth behavior and typically leads to the interaction effects. In the proposed method, a modified crack closure model deriving from the local plastic deformation is employed to account for this load memory effect. In general, this model can simulate the fatigue crack growth under variable amplitude loading. Additionally, this model is established on the physical state of crack tip in the small spatial and temporal scale, and it is used to evaluate the macroscopic crack propagation and fatigue life under irregular tension-tension loading. A special superimposed loading case is discussed to demonstrate the advantage of the proposed model, while the traditional two-parameter approach is not proper functional. Moreover, the typical various load spectra are also employed to validate the method. Good agreements are observed.

Highlights

Since the damage tolerance concept is of great significance to the engineering design, the prediction of fatigue crack growth life under the service environment becomes a prerequisite
Many fatigue-critical structures are usually subjected to variable amplitude (VA) loading condition. e fatigue analysis in this case has to encounter high nonlinear mechanisms of damage accumulation
The computation results in the internal of a cycle are discontinuous by using these aforementioned methods. e requirement of cycle counting before predicting the fatigue crack growth is inevitable, which leads to the fundamental incapacity to utilize the load sequence information

Summary

Introduction

Since the damage tolerance concept is of great significance to the engineering design, the prediction of fatigue crack growth life under the service environment becomes a prerequisite. Afterwards, the forward and reverse plastic zone interaction is considered to be an essential characteristic of load sequence effects [7, 8] Based on this hypothesis, Zhang et al introduced a novel parameter, da/dS, to define the fatigue crack propagation rate with the stress variation at any moment of a cycle [7]. The fatigue crack growth behavior is simultaneously determined by the current applied loads and the physical state ahead of the crack tip. In this investigation, the driving parameters are designated to be the current loading and the CTOD variation which is under the in uence of the plastic-induced crack closure.

Methodology

Model Validation

Findings

Conclusions