Fatigue crack propagation in biaxial stress fields

The main aim of this article is to understand whether biaxial stress fields have a significant impact on the rate of growth of fatigue cracks. Many components in engineered products are subjected to complex, multiaxial stress fields during their operation. However, crack growth behavior is normally evaluated in relatively simple laboratory specimens where the crack grows in a uniaxial stress field. It is important to understand whether multiaxiality can increase fatigue crack growth rates and result in an unsafe fatigue life prediction. The effect of stress field multiaxiality on the propagation behavior of fatigue cracks is reviewed. For a particular case where significant effects have been noted, using a cruciform specimen, a full three-dimensional stress analysis of the specimen has been performed, and the experimental results have been reassessed. It has been found that the relationship between the biaxial load ratio applied to the arms of the specimen and the resulting biaxial stress ratio at the center of the specimen gauge area is not simple; when re-analyzed, the results presented in the referenced paper show no significant effect of biaxial stress ratio on fatigue crack propagation behavior. Reasons for this are discussed, and recommendations are made for future research where significant effects may be noted.