Influence of various hypotheses on the fatigue life evaluation of a cracked round bar

Cylindrical bodies are parts of many engineering structures such as cables, composites and concrete constructions. The fatigue growth analysis of surface cracks in these components is of great interest to the safe design of the whole structure. The problem is very complex since a three-dimensional computation is necessary to obtain the values of the stress intensity factors along the crack front. However, some simplifications come from the observation of cracked round bars subjected to tension or bending loadings. When the crack is deep enough, the opening mode becomes preponderant and the direction of propagation is perpendicular to the bar axis. More precisely, the geometry of the crack front may be approached by an elliptical-are intersecting the outer surface at nearly right angles. A numerical model using the finite element method is developed. The stress intensity factor computations are compared with solutions from other works, then the fatigue crack propagation is examined by applying the Paris-Erdogan law. Finally, other assumptions referring to the crack front geometry and the stress intensity factor distribution are added to the initial model, and their effect on the fatigue life prediction and on the evolution of different parameters is discussed.