Modelling of overload effects on fatigue crack initiation in case of carbon steel

Abstract

This paper deals with the modelling of short crack initiation within a microstructure of medium carbon steel under fatigue loading, as well as with the influence of overload on the crack initiation period. Studies on the long crack growth show that the overload introduces first an increase in the crack growth rate that is then followed with a decrease, a so‐called retardation. A micro‐model containing the microstructure of the material is analysed using the finite element method in combination with a model for crack development – the assessment of number of cycles needed for crack initiation was based on the Tanaka–Mura equation. The analysis brings in a correlation between the crack growth rate and the crack length together with the effects of the overload on the crack growth rate. The overload is found to accelerate the short crack growth; however, the following retardation could not be captured due to the inability of the model to produce residual stresses, which are considered to be the main cause of the retardation effect.

Cracking simulation‐based fatigue life assessment

“…High‐stress short fatigue cracks are subdivided into microstructural short cracks (MSC) and physical small cracks (PSC) . The microstructure has a significant role in the behavior of MSC .…”

Simulation-based Understanding of the Critical Resolved Shear Stress Relevance for the Fatigue Performance of Metallic Materials

“…slip band length) d, the average shear stress range Δτ on the slip band, the shear modulus G, the crack initiation energy Wc, Poisson's ratio ν, and the CRSS [10][11][12][13][14]. A more extended and detailed description of the implementation of the TM equation into FEM-based modelling and simulation of the crack initiation process has been reported in publications of the authors of this study in [5,[10][11][12][15][16][17][18] and by other researchers, too, in [13,14,19,20].…”

“…Multiscale approach-Coupling of methodologies at the relevant scales, and accompanying outputs (O/P) (CRSS, da/dN -crack growth rate, Nini -number of stress cycles for crack initiation, Nprop -number of stress cycles for crack propagation) [5,15,16,23]. Table 1 contains metallic materials considered in the study from [5] and their mechanical properties; namely the Young's modulus E, the shear modulus G, the Poisson's ratio υ, the yield strength Rp0.2 and the ultimate strength Rm, their average grain size d, and eventually the CRSS values.…”

On the Critical Resolved Shear Stress and Its Importance in the Fatigue Performance of Steels and Other Metals with Different Crystallographic Structures

“…These initiation cycles are further transferred to the macroscale fatigue crack growth model based on power law equations (e.g., Paris law), which are finally used to estimate the total fatigue life, up to final fracture. By using the presented modelling workflow, the fatigue of metals can be simulated more or less independently of the experimental input [45,46,[49][50][51][52]. starting with the nanoscale, going up to micro-/mesoscales and ending up with the macroscale.…”