Fatigue Life Prediction of Un-Notched Round Specimens Based on Cracking Simulation

Abstract

This work presents a cracking damage model to assess fatigue lives of un-notched round specimens in axial stresses due to constant and variable amplitude loading. The model numerically simulates collective behavior of growing short fatigue surface cracks originating from the surface roughness of specimens made of a two-phase alloy. The specimen roughness is assumed resembling micro cracks of different sizes and locations along the minimum specimen circumference. Material grains of different phases, sizes and strengths are randomly distributed over that circumference. To verify the model, this work utilized published experimental data on round specimens made of ferritic-pearlitic steel and tested in push-pull constant and variable amplitude loading with (a) two-step high-low and low-high sequences, (b) repeated two-step loading blocks. To simulate laboratory testing, different specimens were randomly configured and virtually tested. Comparison of the experimental results and corresponding predictions shows the validity of the model.

Fracture mechanics approach to fatigue crack initiation at uniaxially loaded notches

“…Consequently, the sum of the lengths of cracks present on the notch surface at the root continuously increases with N . Farag et al 52–54 concluded a similar pattern of short fatigue cracks growing from the rough surface of unnotched round specimens made of a two‐phase alloy.…”