Influence of Crystalline Elasticity on the Stress Distribution at the Free Surface of an Austenitic Stainless Steel Polycrystal. Comparison with Experiments

Abstract

This numerical study focuses on the recent observations of Man et al. [4] showing welloriented grains presenting no Persistent Slip Marking even if PSMs are observed in 86% of the surface grains in 316L austenitic stainless steel cycled at room temperature up to 60% of fatigue life. Scanning Electron Microscopy (SEM) permits us to build Finite Element (FE) meshes of the observed aggregates and to assign to the modelled grains the crystallographic orientations measured by Electron Back Scattering Diffraction (EBSD). Then, 3D FE computations using crystalline elasticity allow the evaluation of mean grain stress tensors and resolved shear stresses. The results could explain qualitatively the anomalous behaviour of the studied well-oriented grains which is partly due to the particular orientations and shapes of the neighbour grains. This study highlights the influence of crystalline elasticity and neighbour grains in microplasticity and crack nucleation.

3-D growth of a short fatigue crack within a polycrystalline microstructure studied using combined diffraction and phase-contrast X-ray tomography

“…to the local grain orientation and local stress tensor. Although the former is known, the latter is more complex to evaluate as the presence of the crack tip and neighboring grains in this elastically anisotropic mate- rial induce a triaxial stress distribution different from the macroscopically applied uniaxial loading [39]. An illustration of this point can be found in Fig.…”

Physically-Based Simulations of the Cyclic Behavior of FCC Polycrystals

“…Crystalline elasticity and plasticity laws Isotropic elasticity is used for mean-field homogenization whereas cubic elasticity is used in the FE computations. The values of the elasticity parameters can be found in [3,9]. The used crystal plasticity constitutive laws are described in details in [6] and are valid for FCC metals with medium stacking fault energy (nickel, copper, 316L) [1,2,12].…”

“…Such computations explain for instance why some well-oriented surface grains display no slip localization even when almost all grains. In fact, neighbour grain effects and the strong anisotropy of crystalline elasticity of austenite may explain qualitatively such discrepancies [9]; -The computation of mean grain stresses and plastic strains allow the prediction of the distributions of the number of cycles to microcrack initiation and crack network evolution [10,11]. Nevertheless, most of the homogenization computations are based on the adjustment of crystal plasticity parameters by inverse identification using experimental macroscopic curves.…”

Extrusions and intrusions in fatigued metals. Part 2. AFM and EBSD study of the early growth of extrusions and intrusions in 316L steel fatigued at room temperature

“…They found that the critical shear stress for PSB formation can be changed in dependence on the neighbor grain orientation. Sauzay and Man [50] showed for some grains without PSMs that in the dependence on the size and the orientation of neighbor grains the 'effective' Schmid factor could be reduced by 24% relative to the 'classical' Schmid factor obtained by EBSD; its value was assessed using the cumulated probability of the Schmid factor given in [49] to about 0.34.…”