MESOSCALE DEFORMATION-INDUCED SURFACE PHENOMENA IN LOADED POLYCRYSTALS

The paper reviews the results of numerical analyses for the micro-and mesoscale deformation-induced surface phenomena in three-dimensional polycrystals with the explicit account for the grain structure. The role of the free surface and grain boundaries in the appearance of the grain-scale stress concentrations and plastic strain nucleation is illustrated on the examples of aluminum polycrystals. Special attention is paid to the discussion of mesoscale deformation-induced surface roughening under uniaxial tension

ON THE PROBLEM OF STRAIN LOCALIZATION AND FRACTURE SITE PREDICTION IN MATERIALS WITH IRREGULAR GEOMETRY OF INTERFACES

The interfacial mechanisms of the stress-strain localization in non-homogeneous media are investigated, using a steel substrate - iron boride coating composition subjected to tension as an example. A dynamic boundary-value problem in a plane-strain formulation is solved numerically by the finite-difference method. The curvilinear substrate-coating interface geometry is assigned explicitly in calculations and is in agreement with experiment. Constitutive relations accounting for an elastic-plastic response of the isotropically-hardened substrate and for a brittle fracture of the coating are employed. Three stages of the plastic strain localization in the steel substrate are found to occur due to the irregular interface geometry. Distributions of the stress concentration regions in the coating are shown to be different at different stages. The stress concentration in the coating is demonstrated to increase nonlinearly during the third stage. The location of fracture is found to depend on the strength of the coating

Numerical analysis of strain-induced surface phenomena in aluminum alloys

Mesoscale surface deformation in polycrystalline aluminum alloys subjected to uniaxial tension is numerically investigated. Three-dimensional polycrystalline models with equiaxial and extended grains peculiar to rolling are constructed by a step-by-step packing method. Calculation results have shown that the grain structure is responsible for the mesoscale surface roughening under uniaxial tension. The roughness pattern is affected by the microstructure and loading conditions. In a specimen with equiaxial grains and in a textured material loaded across the rolling direction surface relief is very pronounced in comparison with the extended grain structure loaded along rolling direction

A computational analysis of the interfacial curvature effect on the strength of a material with a modified surface layer

The mechanisms of the deformation and fracture of coated materials with varying coating thickness and coating-substrate interfacial curvature parameters are investigated. The boundary-value problem in the plane strain formulation is solved numerically, using the finite-difference method. In the calculations, an explicit account is taken of experimental and model microstructures with irregular and sinusoidal coating-substrate interface geometries, respectively. The stress concentration in the near-interface region is shown to increase with decrease in the coating thickness and increase in the sinusoidal interface amplitude. This dependence is nonlinear in character

Numerical study of the surface-hardening effect on surface phenomena in 3D polycrystalline specimens

Surface hardening effect on the mesoscale surface deformation in polycrystalline specimens subjected to uniaxial tension is numerically studied. Basing on the experimental findings, three-dimensional microstructure-based constitutive models of the unhardened and surface-hardened polycrystalline specimens are constructed. The mechanical behavior of the polycrystalline models is analysed numerically by the finite-difference method. The grain structure is shown to be responsible for the free surface roughening under uniaxial loading. Microscale stresses acting in the bulk of the material across the free surface give rise to the formation of surface ridges and valleys. The hardened layer in a surface-hardened specimen moves the grain structure away from the free surface, thus smoothing out the microscale folds caused by displacements of individual grains. The thicker is the modified layer, the smoother is the surface relief

A numerical simulation of the deformation and fracture of a material with a porous polysilazane coating

A numerical analysis of the deformation and fracture mechanisms involved in a material with a porous ceramic coating under tension and compression is presented. The dynamic boundary-value problem in the plane strain formulation is solved numerically by the finite difference method. To take an explicit account of the substrate-coating interface and porous coating microstructure in the calculations, a curvilinear mesh generation algorithm based on the solution according to elasticity theory has been developed. A two-dimensional curvilinear mesh generated in this work was used to simulate the uniaxial loading of a material with a porous coating. The fundamental difference between the fracture mechanisms operating in the coated material in the cases of tension and compression was found to be related with the formation of local regions experiencing bulk tension in both cases

The influence of bi-layer metal-matrix composite coating on the strength of the coated material

Deformation and fracture in aluminum with a bi-layer composite coating are studied numerically. Dynamic boundary-value problems in the plane-stress formulation are solved by the finite element method, using ABAQUS/Explicit. Isotropic elastoplastic and elastic-brittle constitutive models are used to simulate the mechanical response of the aluminum matrix and carbide ceramic particles, respectively. Microstructure of the composite coatings takes into account the complex shape of particles explicitly. To investigate the crack initiation and propagation in ceramic particles, a Huber type fracture criterion was chosen that takes into account the type of local stress state: bulk tension or compression. The influence of the arrangement of the coating layers on the fracture of ceramic particles and on the macroscopic strength of the coated materials is studied. Plastic strain localization, crack patterns and residual stress formation are numerically investigated during cooling followed by tension of the coated materia