Search results for "Polycrystalline material"
showing 10 items of 45 documents
An enhanced grain-boundary framework for computational homogenization and micro-cracking simulations of polycrystalline materials
2015
An enhanced three-dimensional (3D) framework for computational homogenization and intergranular cracking of polycrystalline materials is presented. The framework is aimed at reducing the computational cost of polycrystalline micro simulations, with an aim towards effective multiscale modelling. The scheme is based on a recently developed Voronoi cohesive-frictional grain-boundary formulation. A regularization scheme is used to avoid excessive mesh refinements often induced by the presence of small edges and surfaces in mathematically exact 3D Voronoi morphologies. For homogenization purposes, periodic boundary conditions are enforced on non-prismatic periodic micro representative volume ele…
A micro-mechanical model for grain-boundary cavitation in polycrystalline materials
2015
In this work, the grain-boundary cavitation in polycrystalline aggregates is investigated by means of a grain-scale model. Polycrystalline aggregates are generated using Voronoi tessellations, which have been extensively shown to retain the statistical features of real microstructures. Nucleation, thickening and sliding of cavities at grain boundaries are represented by specific cohesive laws embodying the damage parameters, whose time evolution equations are coupled to the mechanical model. The formulation is presented within the framework of a grain-boundary formulation, which only requires the discretization of the grain surfaces. Some numerical tests are presented to demonstrate the fea…
A three-dimensional grain boundary formulation for microstructural modeling of polycrystalline materials
2013
Abstract A three-dimensional grain boundary formulation is presented for the analysis of polycrystalline microstructures. The formulation is based on a boundary integral representation of the elastic problem for the single grains of the polycrystalline aggregate and it is expressed in terms of the intergranular fields, namely displacements and tractions, that play an important role in polycrystalline micromechanics. The artificial polycrystalline morphology is represented using the Hardcore Voronoi tessellation, which is simple to generate and able to embody the main statistical features of polycrystalline microstructures. The details of the microstructure generation and meshing, which invo…
A grain-scale model for high-cycle fatigue degradation in polycrystalline materials
2018
Abstract A grain-scale three-dimensional model for the analysis of fatigue intergranular degradation in polycrystalline materials is presented. The material microstructure is explicitly represented through Voronoi tessellations, of either convex or non-convex domains, and the mechanics of individual grains is modelled using a boundary integral formulation. The intergranular interfaces degrade under the action of cyclic loads and their behaviour is represented employing a cohesive zone model embodying a local irreversible damage parameter that evolves according to high-cycle continuum damage laws. The model is based on the use of a damage decomposition into static and cyclic contributions, a…
Modelling intergranular and transgranular micro-cracking in polycrystalline materials
2018
Abstract In this work, a grain boundary formulation for intergranular and transgranular micro-cracking in three-dimensional polycrystalline aggregates is presented. The formulation is based on the displacement and stress boundary integral equations of solid mechanics and it has the advantage of expressing the polycrystalline problem in terms of grain boundary variables only. The individual grains within the polycrystalline morphology are modelled as generally anisotropic linear elastic domains with random spatial orientation. Transgranular micro-cracking is assumed to occur along specific cleavage planes, whose orientation in space within the grains depend upon the crystallographic lattice.…
A grain boundary formulation for crystal plasticity
2016
Abstract A three-dimensional grain-boundary formulation for small strains crystal plasticity is presented for the first time. The method is developed and implemented for both single grains and polycrystalline aggregates and it is based on the use of a suitable set of boundary integral equations for modelling the individual grains, which are represented as anisotropic elasto-plastic domains. In the boundary integral framework, crystal plasticity is modelled resorting to an initial strains approach and specific aspects, related to the integration of strongly singular volume integrals in the anisotropic elasto-plastic grain-boundary equations, are discussed and suitably addressed for the first…
A Grain-Scale Model of Inter-Granular Stress Corrosion Cracking in Polycrystals
2017
In this contribution, we propose a cohesive grain-boundary model for hydrogen-assisted inter-granular stress corrosion cracking at the grain-scale in 3D polycrystalline aggregates. The inter-granular strength is degraded by the presence of hydrogen and this is accounted for by employing traction-separation laws directly depending on hydrogen concentration, whose diffusion is represented at this stage through simplified phenomenological relationships. The main feature of the model is that all the relevant mechanical fields are represented in terms of grain-boundary variables only, which couples particularly well with the employment of traction-separation laws.
A microstructural model for homogenisation and cracking of piezoelectric polycrystals
2019
Abstract An original three-dimensional generalised micro-electro-mechanical model for computational homogenisation and analysis of degradation and micro-cracking of piezoelectric polycrystalline materials is proposed in this study. The model is developed starting from a generalised electro-mechanical boundary integral representation of the micro-structural problem for the individual bulk grains and a generalised cohesive formulation is employed for studying intergranular micro-damage initiation and evolution into intergranular micro-cracks. To capture the electro-mechanical coupling at the evolving damaging intergranular interfaces, standard mechanical cohesive laws are enriched with suitab…
Grain-boundary modelling of hydrogen assisted intergranular stress corrosion cracking
2018
Abstract A novel hybrid strategy for modelling intergranular hydrogen embrittlement in polycrystalline microstructures is proposed. The technique is based on a grain-boundary integral representation of the polycrystalline micro-mechanics, numerically solved by the boundary element method, coupled with an explicit finite element model of the intergranular hydrogen diffusion. The intergranular interaction between contiguous grains in the aggregate is modelled through extrinsic cohesive-frictional traction-separation laws, whose parameters depend on the concentration of intergranular hydrogen, which diffuses over the interface according to the Fick’s second law, inducing the weakening of the i…
Micro-cracking of brittle polycrystalline materials with initial damage
2016
In this paper, the effect of pre-existing damage on brittle micro-cracking of polycrystalline materials is explored. The behaviour of single and multiple cracks randomly distributed within a grain scale polycrystalline aggregate is investigated using a recently developed grain boundary 3D computational framework. Each grain is modelled as a single crystal anisotropic domain. Opening, sliding and/or contact at grain boundaries are modelled using nonlinear cohesive-frictional laws. The polycrystalline micro-morphologies are generated using Voronoi tessellation algorithms in combination with a regularisation scheme to avoid the presence of unnecessary small geometrical entities (edges and face…