Crystal plasticity model calibration for 316l stainless steel single crystals during deformation

Type 316L austenitic stainless steel is an important structural material used for the in-core components and pressure boundaries of light water reactors. In order to study degradation mechanisms in such a steel, like crack initiation and propagation, it is crucial to develop reliable crystal plasticity models at microscale that would account for anisotropic nature of the material and realistic modelling of grain topology. In this work we present a procedure for calibrating material properties of a slip-based crystal plasticity finite element model and investigate its suitability as a constitutive model for single-crystal tensile test simulations. The material properties include the anisotropic elastic and crystal plasticity material parameters that are calibrated against experimental tensile test curves for 316L stainless steel single crystals at selected crystallographic orientations. For the crystal plasticity material parameters a systematic sensitivity study using Bassani and Wu hardening law is performed

Grain boundary stresses in elastic materials

A simple analytical model of intergranular normal stresses is proposed for a general elastic polycrystalline material with arbitrary shaped and randomly oriented grains under uniform loading. The model provides algebraic expressions for the local grain-boundary-normal stress and the corresponding uncertainties, as a function of the grain-boundary type, its inclination with respect to the direction of external loading and material-elasticity parameters. The knowledge of intergranular normal stresses is a necessary prerequisite in any local damage modeling approach, e.g., to predict the intergranular stress-corrosion cracking, grain-boundary sliding or fatigue-crack-initiation sites in structural materials. The model is derived in a perturbative manner, starting with the exact solution of a simple setup and later successively refining it to account for higher order complexities of realistic polycrystalline materials. In the simplest scenario, a bicrystal model is embedded in an isotropic elastic medium and solved for uniaxial loading conditions, assuming 1D Reuss and Voigt approximations on different length scales. In the final iteration, the grain boundary becomes a part of a 3D structure consisting of five 1D chains with arbitrary number of grains and surrounded by an anisotropic elastic medium. Constitutive equations can be solved for arbitrary uniform loading, for any grain-boundary type and choice of elastic polycrystalline material. At each iteration, the algebraic expressions for the local grain-boundary-normal stress, along with the corresponding statistical distributions, are derived and their accuracy systematically verified and validated against the finite element simulation results of different Voronoi microstructures.Comment: 28 pages, 20 figure

Phase behaviour of colloidal assemblies on 2D corrugated substrates

We investigate - with Monte Carlo computer simulations - the phase behaviour of dimeric colloidal molecules on periodic substrates with square symmetry. The molecules are formed in a two-dimensional suspension of like charged colloids subject to periodic external confinement, which can be experimentally realized by optical methods. We study the evolution of positional and orientational order by varying the temperature across the melting transition. We propose and evaluate appropriate order parameters as well as the specific heat capacity and show that the decay of positional correlations belongs to a class of crossover transitions while the orientational melting is a second-order phase transition.Comment: 13 pages, 9 figures, accepted in J. Phys.: Condens. Matte

Colloidal ionic complexes on periodic substrates: ground state configurations and pattern switching

We theoretically and numerically studied ordering of "colloidal ionic clusters" on periodic substrate potentials as those generated by optical trapping. Each cluster consists of three charged spherical colloids: two negatively and one positively charged. The substrate is a square or rectangular array of traps, each confining one such cluster. By varying the lattice constant from large to small, the observed clusters are first rod-like and form ferro- and antiferro-like phases, then they bend into a banana-like shape and finally condense into a percolated structure. Remarkably, in a broad parameter range between single-cluster and percolated structures, we have found stable supercomplexes composed of six colloids forming grape-like or rocket-like structures. We investigated the possibility of macroscopic pattern switching by applying external electrical fields.Comment: 14 pages, 13 figure

Combining Single- and Poly-Crystalline Measurements for Identification of Crystal Plasticity Parameters: Application to Austenitic Stainless Steel

Crystal plasticity finite element models have been extensively used to simulate various aspects of polycrystalline deformations. A common weakness of practically all models lies in a relatively large number of constitutive modeling parameters that, in principle, would require dedicated measurements on proper length scales in order to perform reliable model calibration. It is important to realize that the obtained data at different scales should be properly accounted for in the models. In this work, a two-scale calibration procedure is proposed to identify (conventional) crystal plasticity model parameters on a grain scale from tensile test experiments performed on both single crystals and polycrystals. The need for proper adjustment of the polycrystalline tensile data is emphasized and demonstrated by subtracting the length scale effect, originating due to grain boundary strengthening, following the Hall–Petch relation. A small but representative volume element model of the microstructure is identified for fast and reliable identification of modeling parameters. Finally, a simple hardening model upgrade is proposed to incorporate the grain size effects in conventional crystal plasticity. The calibration strategy is demonstrated on tensile test measurements on 316L austenitic stainless steel obtained from the literature

Crystal plasticity model calibration for 316l stainless steel single crystals during deformation

Type 316L austenitic stainless steel is an important structural material used for the in-core components and pressure boundaries of light water reactors. In order to study degradation mechanisms in such a steel, like crack initiation and propagation, it is crucial to develop reliable crystal plasticity models at microscale that would account for anisotropic nature of the material and realistic modelling of grain topology. In this work we present a procedure for calibrating material properties of a slip-based crystal plasticity finite element model and investigate its suitability as a constitutive model for single-crystal tensile test simulations. The material properties include the anisotropic elastic and crystal plasticity material parameters that are calibrated against experimental tensile test curves for 316L stainless steel single crystals at selected crystallographic orientations. For the crystal plasticity material parameters a systematic sensitivity study using Bassani and Wu hardening law is performed

Ground states of colloidal molecular crystals on periodic substrates

12 pages, 13 figuresInternational audienceTwo dimensional suspensions of spherical colloids subject to periodic external fields exhibit a rich variety of molecular crystalline phases. We study in simulations the ground state configurations of dimeric and trimeric systems, that are realized on square and triangular lattices, when either two or three macroions are trapped in each external potential minimum. Bipartite orders of the checkerboard or stripe types are reported together with more complex quadripartite orderings, and the shortcomings of envisioning the colloids gathered in a single potential minimum as a composite rigid object are discussed. This work also sheds light on simplifying assumptions underlying previous theoretical treatments and that made possible the mapping onto spin models

CALIBRATION OF AN ANISOTROPIC PLASTICITY FINITE ELEMENT MODEL OF A POLYCRYSTAL IN UNIAXIAL TENSION

We propose a simple anisotropic elasto-plastic finite element model to quantify the deformation heterogeneity locally within the grains of a polycrystal under plastic deformation. The model is calibrated against the electron backscatter diffraction measurements on stainless steel under uniaxial tensile loading. The spatial model of the specimen is generated by Voronoi tessellation using initial random orientation of the grains. The calibration of the model is provided by statistical means by calculating and comparing the crystal deformation parameter, which quantifies the spread of the crystal orientation within individual grains from the central grain orientation. It is confirmed that this parameter has a good correlation to the degree of the plastic strain.JRC.F.4-Nuclear Reactor Integrity Assessment and Knowledge Managemen

Dimeric and dipolar ground state orders in colloidal molecular crystals

A two dimensional colloidal suspension subject to a periodic substrate evolves into a colloidal molecular crystal under situationsofstrongconfinement. Wefocusonthelongrangeorientationalordertherebyemerging, inthegroundstate. We study by simulations the situations where in each trap lies a pair of identical colloids, or alternatively a pair of oppositelychargedmacroions. We consider square or triangular geometries for the periodic confinement, together with less symmetric distorted lattices