Fatigue Crack Growth from Notches: A Numerical Analysis

Abstract

A numerical approach based on plastic crack tip opening displacement (CTOD) was followed to study fatigue crack growth (FCG) from notches. The identification of fundamental mechanisms was made considering notched and unnotched models, with and without contact of crack flanks. Different parameters were studied, namely, notch radius, crack length, stress state, and material. The notch increases the plastic CTOD, and therefore fatigue crack growth rate, da/dN, as expected. The reduction of notch radius increases da/dN but reduces the notch affected zone. Ahead of the notch affected zone, da/dN increases linearly with crack growth, with a rate that increases linearly with the plastic CTOD. The crack closure phenomenon has a dramatic effect under plane stress conditions but a limited effect on plane strain conditions. In the former case, the contact of crack flanks reduces substantially the effect of notch radius and the size of the notch affected zone. These trends are associated with the increase of crack closure level with notch radius. The material does not affect the global trends, but the reduction of yield stress increases the level of plastic deformation and therefore da/dN. The effect of material, and also of stress state, is mainly associated with crack closure.

Effect of Residual Stresses on Fatigue Crack Growth: A Numerical Study Based on Cumulative Plastic Strain at the Crack Tip

“…The increase in the FCG rate with the crack length is now more pronounced than observed with crack closure (and no TRS). A similar trend was observed in the propagation of cracks from notches [ 48 ]. However, more importantly, the results with TRS are now coincident with the predictions obtained without TRS.…”

Crack Tip Radius Effect on Fatigue Crack Growth and Near Tip Fields in Plastically Compressible Materials

“…The plastic compressibility together with material softening diminishes the amount of growth significantly. The present FCG for plastically incompressible solids shows the similar trend (in a qualitative way) when we compare our results with those of Rozumek 7 , et al, Toribio and Kharin 22 , Borges 23 , et al. distributions corresponding to the tip radius of 0.01.…”

Numerical Prediction of the Fatigue Crack Growth Rate in SLM Ti-6Al-4V Based on Crack Tip Plastic Strain

“…A linear correlation was found between the plastic crack tip opening displacement (CTOD), determined experimentally [14] or numerically [15], and da/dN. This approach was used to predict the effect of material properties [16] and notch geometry [17], among other aspects. An alternative approach, based on cumulative plastic strain measured immediately of crack tip, was applied successfully to predict the FCG rate in the 2024-T351 aluminium alloy [18].…”