Simulating small crack growth behaviour using crystal plasticity theory and finite element analysis

Abstract

A B S T R A C T Predictions of small crack growth under cyclic loading in aluminium alloy 7075 are performed using finite element analysis (FEA), and results are compared with published experimental data. A double-slip crystal plasticity model is implemented within the analyses to enable the anisotropic nature of individual grains to be approximated. Small edge-cracks in a single grain with a starting length of 6 µm are incrementally grown following a noderelease scheme. Crack-tip opening displacements (CTOD) and crack opening stresses are calculated during the simulated crack growth, and da/ dN against K diagrams are computed. Interactions between the crack tip and a grain boundary are also considered. The computations are shown to accurately capture the magnitude and the variability normally observed in small crack fatigue data.

Influence of microstructure variability on short crack behavior through postulated micromechanical short crack driving force metrics

“…For this reason, additional insight is needed to capture the complexity of SCG behavior. The multiaxiality of the stress fields resulting form uniaxial loading (at the GBs and at the crack tip) and the anisotropic behavior of the plastic zones found in our simulations are in agreement with the results found by Guilhem et al [11] and Potirniche et al [10], respectively. Fig.…”

“…5(d) and (e), respectively, we note that, despite the similarities in the cracked grain orientation and the corresponding stress fields, the average level of the von Mises stress ahead of the crack tip shows a variability of around 200 MPa. In both cases, the differences in the hot/cold spots extension and position suggest that the crack may grow at different rates in different directions due to the presence of GBs [10] and misorientation between neighboring grains [8,9]. Furthermore, the different behavior experienced by neighbor grains indicates the need to analyze clusters of grains, as pointed out by Guilhem et al [11]and Sangid et al [12] in the context of a microstructure-sensitive SCG theory.…”

“…Ferrie et al [9] investigated the relationship between Stage I crack growth rate and the orientation of the neighboring grain through the calculation of crack tip opening displacement and crack tip sliding displacement, finding an orientation dependence. Potirniche et al [10] showed that variability in SC growth rate could be reproduced in simulations changing the orientation of the neighboring grain. These studies serve as the basis for understanding complex SC behavior and emphasize the need to explore the complete space of complex 3-D behavior, due to the interaction of multiple microstructure attributes, such as grain clustering which constitutes an important feature for fatigue analysis [11,12].…”

A crystal plasticity study of cyclic constitutive behaviour, crack-tip deformation and crack-growth path for a polycrystalline nickel-based superalloy

“…Also, grain orientation mismatch leads to the change of slip plane across the grain boundaries [30], resulting in a zig-zag pattern for crack growth [31]. In terms of modelling, a combination of crystal plasticity and simplified grain-structure modelling has been applied to study crack tip displacements, crack tip plasticity and crack opening/closure stress [26,[32][33][34][35]. It was concluded that both crack tip opening and sliding displacements contribute to the crack growth [26], and plastic zone size significantly depends on the crystallographic orientation [32].…”

Crack tip displacements of microstructurally small cracks in 316L steel and their dependence on crystallographic orientations of grains

“…17 Other crack blocking models use separate equations and simply state that a long crack equation should be adopted if the threshold stress intensity factor is reached. 18 In recent years several attempts have been made to model the behaviour of long cracks in single crystal 19 and small cracks in bicrystal 20 and polycrystals 21,22 using crystal plasticity material models but basically without the explicit grain shape modelling. Models with one, two 9,23,24 and more 24 explicitly modelled grains can be found in literature but they assume a rectangular grain shape.…”