K Variations and Anisotropy: Microstructure Effect and Numerical Predictions

Abstract

Computer experiments were performed on simulated polycrystalline material samples that possess locally anisotropic microstructures to investigate stress intensity factor (K) variations and anisotropy along fronts of microcracks of different sizes. The anisotropic K, arising from inhomogeneous stresses in broken grains, was determined for planar microcracks by using a weight function-based numerical technique. It has been found that the grain-orientation-geometry-induced local anisotropy produces large variations in K along front of microcracks, when the crack size is of the order of few grain diameters. Synergetic effect of grain orientation and geometry of broken grains control K variations and evolution along the microcrack front. The K variations may diminish at large crack sizes, signifying a shift of K calculation to bulk stress dependence from local stress dependence. Local grain geometry and texture may lead to K anisotropy, producing unusually higher/ lower K at a segment of the crack front. Either K variation or anisotropy cannot be ignored when assessing a microcrack.

Effect of welding process and groove angle on type IV cracking behaviour of weld joints of a ferritic steel

“…This implies that both triaxiality and strain are highest at the same location in the weld joints and this is also the location at which maximum creep damage is observed. Modelling of type IV cracking by other workers 8,16,17 has also produced similar results.…”

“…Thus, as already summarised by Li et al 17 recently, high equivalent strain and high triaxial stress in the FGHAZ influence the type IV cracking significantly. High equivalent strain in this zone facilitates the nucleation of the creep voids while the high triaxial stress, as already pointed out, assists the growth of these voids which in turn leads to cracking and final fracture.…”

Study on Model of Meso-Scale Simulation for Aircraft Structure Material Based on Voronoi Algorithm

“…In many material science studies crystal structures need to be established models, which are divided into two kinds on the whole: a dynamic model and a static model. The dynamic model usually adopts Monte Carlo method while setting up histology framework, which involves solidifying and growth course of the crystalline grain; The static model, which do not consider the growth of the crystalline grain, is suitable for dealing with the relationship between size and orientation of crystalline grains [3,4]. In this, the method based on Voronoi algorithm is adopted to create a two-dimensional crystalline grain structure of the polycrystalline materials.…”

Fatigue crack growth in polysilicon microstructures subjected to multi-axial loading: A Poisson–Voronoi-based finite element analysis

“…For example, the elastic anisotropy of crystals and the stress singularities arising at grain corners [10][11][12] can greatly affect the stress distribution at the grain level, further exacerbating stress singularity effects, depending on the anisotropy and orientation of the grains [12]. Grain orientation-induced local anisotropy may lead to large variations of the stress intensity factor (SIF) when the crack size is of the order of a few grain diameters [13]. Grain anisotropy in a nickel-based superalloy yielded a stepwise variation of the J-integral with the crack length, which was attributed to changes in transgranular crack growth rate [14].…”