Numerical fracture mechanics as a practical failure investigatory tool: The outlook of cracked round bars

Abstract

Many failure investigations related to the failed round bars/shafts for various applications have been reported in literature. The cracks were often initiated at the regions with a high stress concentration. However, numerical fracture mechanics was frequently not used in the failure investigations. Nowadays advancement of computational development on the interactive numerical techniques allows the analysts to more accessibly figure out the fracture phenomena when performing engineering analyses. In addition, the computational cost is no longer the issue of performing numerical fracture mechanics analyses. The stress intensity factors (SIFs) of a surface planar flaw at a stepped round bar are of practical interest, however, the SIF solutions along the flaw front were not yet documented in literature. Here, the practical abilities of the numerical fracture mechanics on the fracture analyses are demonstrated by evaluating a planar surface flaw at the shoulder fillet through numerical simulations by the finite element method (FEM) and the dual boundary element method (DBEM). The use of tetrahedral meshing of FEM is presented, and the concern of corner point singularity on a surface planar flaw is highlighted. The stress contours around the front of planar flaws that are hardly acknowledged in literature are also presented. The SIF behaviors of the semi-elliptical planar flaws are discussed. The SIF data for relatively small crack sizes are valuable to be used for judging a condition of crack size whether or not it would grow to a critical size.