| Fatigue failure in mechanical components is one of the main concerns of the aircraft industry, so compressive residual stress is often applied to the components because it is beneficial to improve resistance to fatigue by slowing down crack growth. As a result, residual stress has been included in fatigue crack growth prediction methods. To date, residual stress was usually combined with applied loads to affect the stress intensity factor (at the current crack size) in the fatigue crack growth prediction. However, crack face contact may occur due to compressive residual stress during fatigue crack growth, and the contact effect was barely included in the prediction. Crack face contact near the crack tip under cyclic loading due to plasticity or roughness, which is called fatigue crack closure, has been studied extensively because it has a significant effect on fatigue crack growth rate (FCGR), but little research has been conducted to understand the details of crack closure due to bulk residual stress fields.;This work focuses on crack closure due to compressive residual stress in an elastic material with bulk residual stress, and emphasizes that the effect of bulk residual stresses on crack closure described here is an elastic effect, which distinguishes it from the more commonly discussed forms of closure. This work describes a means to forecast crack closure due to bulk residual stress fields and assesses schemes to account for its effects on fatigue crack growth. First, contact pressure between two opposing crack faces is quantified with modeling the problem of frictionless contact. In the modeling, a weight function for a specific geometry is used and the problem is solved using quadratic mathematical programming. Second, the contact pressure is included as a form of stress intensity factor to the fatigue crack growth prediction, and the new prediction method is suggested. The new prediction method is compared to the previous methods in the literature for specific geometries (a crack on compact tension coupons and a radial crack at a hole in a strip), applied loads and residual stress fields. Additionally, in order to support this work, weight functions for cracks at a hole were newly developed. |
