Fatigue crack closure as a function of crack length in AlLi alloys

Abstract

A simple analytical model that is analogous to the experimental procedure for determining crack closure load has been developed to predict variations of closure stress intensity factors as a function of crack length. From the analysis, the variation of closure stress intensity factors was shown to be directly correlated to the roughness dimension (or asperity height) on crack surfaces. When the asperity height is relatively high as compared to the crack length, the closure stress intensity factors become a function of the crack length. Otherwise, the closure stress intensity factors appear to be essentially independent of the crack length. Also, an efficient method for estimating the experimental closure load and stress intensity factor has been developed using crack surface opening displacements at the load line. The resulting data, appeared to correlate very well with analytical results. In addition, a model predicting changes in roughness dimension on the crack surface along the crack growth direction was proposed. The roughness dimension on the crack surfaces for the AI-Li alloy used in this study was shown to be a strong function of crack length, decreasing monotonically as the crack length increases depending upon the material constants.