Effect of different boundary conditions on the crack growth mechanism under cycling bending loads

Sometimes, structural components are subjected to service conditions that have not taken into account at the design stage. If it is assumed that an initial flaw exists, according to damage tolerance philosophy the analysis of such components needs to be corroborated by accurate Stress Intensity Factor (SIF) solutions, in order to determine both the crack propagation life and the appropriate inspection intervals. In this study, the effects of the boundary conditions on both the SIF and the crack propagation life have been evaluated for a surface crack existing at the root of a shoulder fillet notch in a round bar under bending. The SIF distribution along the crack front has been calculated for the component object of the study by using the Virtual Crack Closure Technique, whereas a two parameters propagation law has been employed to evaluate the evolution of the crack shape. The results show that, under the same loading conditions, the way the component is constrained strongly influences the fatigue crack growth, due to additional SIF fluctations that might contribute to the crack growth and, in turn, affecting both the number of cycles to failure and the frequency of the inspection intervals