Numerical Simulations of Void Linkage in Model Materials using a Nonlocal Ductile Damage Approximation

Experiments on the growth and linkage of 10 μm diameter holes laser drilled in high precision patterns into Al-plates were modelled with finite elements. The simulations used geometries identical to those of the experiments and incorporated ductile damage by element removal under the control of a ductile damage indicator based on the micromechanical studies of Rice and Tracey. A regularization of the problem was achieved through an integral-type nonlocal model based on the smoothing of the rate of a damage indicator D over a characteristic length L. The simulation does not predict the experimentally observed damage acceleration either in the case where no damage is included or when only a local damage model is used. However, the full three-dimensional simulations based on the nonlocal damage methodology do predict both the failure path and the failure strain at void linkage for almost all configurations studied. For the cases considered the critical parameter controlling the local deformations at void linkage was found to be the ratio between hole diameter and hole spacing

Micromechanics-based constitutive relations for post-localization analysis.

Micromechanics-based constitutive relations for post-localization analysis are obtained, to be used in a multi-surface representation of porous metal plasticity. Each yield surface involves a number of internal parameters. Hence, the constitutive relations must be closed with evolution equations for the internal parameters. The latter are essential to describing the gradual loss of load-bearing capacity under shear-dominated loading. We also briefly discuss potential void closure due to void rotation and elongation in shear and show additional details regarding the simulations reported in a recent paper (A mechanism of failure in shear bands (2018) Extreme Mechanics Letters, 23, pp. 67-71.) The method can be more broadly used in a range of ductile failure problems involving combined tension and shear loadings

Orientation-dependent plastic deformation in transformer steel: Experiments and dislocation dynamics simulations

The anisotropic tensile response of fully processed cold-rolled grain-oriented (CRGO) steel was studied for two crystallographic orientations: (1 1 0) [0 0 1] and (1 1 0) [1 (1) over bar 1]. They showed remarkably different stress strain behavior and corresponding developments in deformed microstructures. The (1 1 0) [0 0 1] oriented CRGO steel specimens retained their orientation stability until epsilon (true strain) = 0.07. On the other hand, (1 1 0) [1 (1) over bar 1] oriented specimens underwent significant reorientation and displayed formation of strain localizations by epsilon = 0.03. Discrete dislocation dynamics (DDD) simulations were carried out - three-dimensional (3-D) for "limited" (similar to 10(-4)) plastic strain and two-dimensional (2-D) for the experimentally imposed strain - to investigate the orientation effects on the tensile response of the CRGO steel specimens. 2-D DDD simulations were able to provide qualitative and quantitative estimates of the post-yield tensile behavior of (1 1 0) [0 0 1] and (1 1 0) [1 (1) over bar 1] samples. Direct comparison between experimental and simulation results confirmed the orientation effect on the overall macroscopic response of the specimens. It was observed that the response of (1 1 0) [1 (1) over bar 1] specimens showed features of reorientation and textural softening and these were captured by the Taylor type deformation simulations. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved

On localization and void coalescence as a precursor to ductile fracture

Two modes of plastic flow localization commonly occur in the ductile fracture of structural metals undergoing damage and failure by the mechanism involving void nucleation, growth and coalescence. The first mode consists of a macroscopic localization, usually linked to the softening effect of void nucleation and growth, in either a normal band or a shear band where the thickness of the band is comparable to void spacing. The second mode is coalescence with plastic strain localizing to the ligaments between voids by an internal necking process. The ductility of a material is tied to the strain at macroscopic localization, as this marks the limit of uniform straining at the macroscopic scale. The question addressed is whether macroscopic localization occurs prior to void coalescence or whether the two occur simultaneously. The relation between these two modes of localization is studied quantitatively in this paper using a three-dimensional elastic-plastic computational model representing a doubly periodic array of voids within a band confined between two semi-infinite outer blocks of the same material but without voids. At sufficiently high stress triaxiality, a clear separation exists between the two modes of localization. At lower stress triaxialities, the model predicts that the onset of macroscopic localization and coalescence occur simultaneously. [GRAPHICS] .The support of the Belgian Science Policy through the IAP 7/21 project is gratefully acknowledged