Fracture mechanics analysis for residual stress and crack closure corrections

Abstract

A new methodology is proposed to determine (1) stress intensity factors due to residual stress, K res, when samples with high residual stress are tested, and (2) effective stress intensity factors, K eff, from corresponding applied stresses when closure contributions are significant. Residual stress is acknowledged to cause changes in the applied stress intensity factors, and these changes are dependent on the residual stress nature (compressive or tensile). Due to the magnified effects of residual stress on long crack growth behavior, corrections for residual stress are needed for appropriate fatigue life evaluations and realistic behavior comparisons. Crack closure, on the other hand, is considered to be the main mechanism leading to differences between applied and effective stress intensity factor ranges at a crack tip. The effective stress intensity factor ranges are important because they represent the major physical cause of fatigue crack growth. Various methods for closure correction have been proposed, but due to their empirical nature and lack of analytical basis, their applicability and general acceptance is limited. The proposed method is an analytical formulation based on load–displacement record differences for incremental changes in crack length. Examples of residual stress and crack closure corrections are provided to validate the method.