Design Life Prediction of Structural Components Subjected to Various Fatigue Loadings

Many structural components are subjected to cyclic loading, fracture being the most common form of failure. Design life assessment and reliability prediction of engineering components for in-service conditions, with the external loads of irregular and random nature, are obviously critical issues. The present work is an investigation of fatigue crack growth rates and design life assessment of the structural components subjected to various types of fatigue loadings. The life prediction has been carried out by linear elastic fracture mechanics (LEFM) principles using commercial package MATLAB(R) and FORTRAN(R) programming language. Modified Wheeler Model (MWM) and Crack Closure Model (CCM) have been applied to evaluate fatigue crack growth and its retardation due to interaction between the materials and various overloads (single, multiple and spectrum). The MWM is based on plasticity induced effects in front and in the wake of an advancing crack and CCM is based on the crack closure effects. Studies on design life assessment of cracked plate panels and other structural members subjected to tensile-compressive overloading-underloading have been carried out for validating these models. Quantitative retardation based on the residual stresses with an effective stress intensity factor has been developed using MWM and applied to the material specimen: plates with center crack-350 WT Steel, 7075-T6 Al- Alloy and plate with edge crack for 6061-T6-Al-Alloy to predict the design life of components under various fatigue loadings. The results obtained have been compared with the experimental results. Various fatigue crack growth rate equations of constant amplitude loading models in conjunction with Wheeler Model have been incorporated in the design life estimation and compared with the experimental data and are in good agreement.