Stress-intensity factor solutions for the simulation of fish-eye fatigue crack growth in round bars subjected to tensile load

Abstract

The fatigue crack growth in round bars initiated from internal defects leads to the formation of a circular crack pattern usually so-called fish-eye. This failure mechanism is found in the current additive manufacturing techniques in which internal defects, such as pores or lack of fusion, are the main cause of fatigue crack initiation. Moreover, this fatigue mechanism becomes the predominant failure mode in the Very High Cycle Fatigue (VHCF) regime. With the aim of adequately studying these fatigue crack situations, this paper presents a set of solutions for the stress-intensity factor calculation for embedded elliptical cracks in a round bar subjected to tensile load. The stress-intensity factors (SIF) are presented in a tabulated form and were obtained from three-dimensional finite-element analyses. The SIF solutions are provided as a function of three dimensionless parameters that include the crack size, the crack aspect ratio, and its relative position in the cross section. After that, a sequential methodology for fatigue crack growth simulation is presented, and a comparison with experimental results of fatigue crack propagation initiated from internal defects in round bars is also presented. Finally, by varying the initial crack position and the initial crack aspect ratio, several aspects related to the evolution of the fatigue crack shape in this geometry are analyzed.