70,354 research outputs found
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
Diffuse-interface polycrystal plasticity: Expressing grain boundaries as geometrically necessary dislocations
The standard way of modeling plasticity in polycrystals is by using the
crystal plasticity model for single crystals in each grain, and imposing
suitable traction and slip boundary conditions across grain boundaries. In this
fashion, the system is modeled as a collection of boundary-value problems with
matching boundary conditions. In this paper, we develop a diffuse-interface
crystal plasticity model for polycrystalline materials that results in a single
boundary-value problem with a single crystal as the reference configuration.
Using a multiplicative decomposition of the deformation gradient into lattice
and plastic parts, i.e. F(X,t) = F^L(X,t) F^P(X,t), an initial stress-free
polycrystal is constructed by imposing F^L to be a piecewise constant rotation
field R^0(X), and F^P = R^0(X)^T, thereby having F(X,0) = I, and zero elastic
strain. This model serves as a precursor to higher order crystal plasticity
models with grain boundary energy and evolution.Comment: 18 pages, 7 figure
Glassy features of crystal plasticity
Crystal plasticity occurs by deformation bursts due to the avalanche-like
motion of dislocations. Here we perform extensive numerical simulations of a
three-dimensional dislocation dynamics model under quasistatic
stress-controlled loading. Our results show that avalanches are power-law
distributed, and display peculiar stress and sample size dependence: The
average avalanche size grows exponentially with the applied stress, and the
amount of slip increases with the system size. These results suggest that
intermittent deformation processes in crystalline materials exhibit an extended
critical-like phase in analogy to glassy systems, instead of originating from a
non-equilibrium phase transition critical point.Comment: 6 pages, 4 figures, Supplemental Material as an ancillary file,
accepted for publication in Phys. Rev.
Excitation spectra in crystal plasticity
Plastically deforming crystals exhibit scale-free fluctuations that are
similar to those observed in driven disordered elastic systems close to
depinning, but the nature of the yielding critical point is still debated.
Here, we study the marginal stability of ensembles of dislocations and compute
their excitation spectrum in two and three dimensions. Our results show the
presence of a singularity in the distribution of {\it excitation stresses},
i.e., the stress needed to make a localized region unstable, that is remarkably
similar to the one measured in amorphous plasticity and spin glasses. These
results allow us to understand recent observations of extended criticality in
bursty crystal plasticity and explain how they originate from the presence of a
pseudogap in the excitation spectrum.Comment: 5 pages, 4 figures, to appear in Phys. Rev. Let
Dislocation transport and line length increase in averaged descriptions of dislocations
Crystal plasticity is the result of the motion and interaction of
dislocations. There is, however, still a major gap between microscopic and
mesoscopic simulations and continuum crystal plasticity models. Only recently a
higher dimensional dislocation density tensor was defined which overcomes some
drawbacks of earlier dislocation density measures. The evolution equation for
this tensor can be considered as a continuum version of dislocation dynamics.
We use this evolution equation to develop evolution equations for the total
dislocation density and an average curvature which together govern a faithful
representation of the dislocation kinematics without having to use extra
dimensions
Anisotropic shock response of columnar nanocrystalline Cu
We perform molecular dynamics simulations to investigate the shock response of idealized hexagonal columnar nanocrystalline Cu, including plasticity, local shear, and spall damage during dynamic compression, release, and tension. Shock loading (one-dimensional strain) is applied along three principal directions of the columnar Cu sample, one longitudinal (along the column axis) and two transverse directions, exhibiting a strong anisotropy in the response to shock loading and release. Grain boundaries (GBs) serve as the nucleation sites for crystal plasticity and voids, due to the GB weakening effect as well as stress and shear concentrations. Stress gradients induce GB sliding which is pronounced for the transverse loading. The flow stress and GB sliding are the lowest but the spall strength is the highest, for longitudinal loading. For the grain size and loading conditions explored, void nucleation occurs at the peak shear deformation sites (GBs, and particularly triple junctions); spall damage is entirely intergranular for the transverse loading, while it may extend into grain interiors for the longitudinal loading. Crystal plasticity assists the void growth at the early stage but the growth is mainly achieved via GB separation at later stages for the transverse loading. Our simulations reveal such deformation mechanisms as GB sliding, stress, and shear concentration, GB-initiated crystal plasticity, and GB separation in nanocrystalline solids under shock wave loading
Phase-field modelling of fracture in single crystal plasticity
We propose a phase-field model for ductile fracture in a single crystal within the kinematically linear
regime, by combining the theory of single crystal plasticity as formulated in Gurtin et al. (2010) and
the phase-field formulation for ductile fracture proposed by Ambati et al. (2015) . The model introduces
coupling between plasticity and fracture through the dependency of the so-called degradation function
from a scalar global measure of the accumulated plastic strain on all slip systems. A viscous regularization
is introduced both in the treatment of plasticity and in the phase-field evolution equation. Testing of
the model on two examples for face centred cubic single crystals indicates that fracture is predicted to
initiate and develop in the regions of the maximum accumulated plastic strain, which is in agreement
with phenomenological observations. A rotation of the crystallographic unit cell is shown to affect the
test results in terms of failure pattern and corresponding global and local response
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