Multiscale Damage Model Research Articles

Multiscale modeling of radiation damage in Fe-based alloys in the fusion environment

Ferritic alloys represent a technologically important class of candidate materials for fusion first wall and blanket structures. A detailed understanding of the mechanisms of defect accumulation and microstructure evolution, and the corresponding effects on mechanical properties is required to predict their in-service structural performance limits. The physical processes involved in radiation damage, and its effects on mechanical properties, are inherently multiscale and hierarchical, spanning length and time scales from the atomic nucleus to meters and picosecond to decades. In this paper, we present a multiscale modeling methodology to describe radiation effects within the fusion energy environment. Selected results from atomic scale investigation are presented, focusing on (i) the mechanisms of self-interstitial dislocation loop formation with Burgers vector of a〈1 0 0〉 in iron relative to vanadium, (ii) helium transport and (iii) the interaction between helium and small self-interstitial clusters in iron, and (iv) dislocation-helium bubble interactions in fcc aluminum.

Multiscale modeling of damage and failure in aluminum-matrix composites

A multiscale approach to composite failure, in which detailed information on small-scale micromechanics is incorporated approximately yet accurately into larger-scale models capable of simulating extensive damage evolution and ultimate failure, is applied to the deformation and failure of an aluminum matrix composite reinforced with Al 2O 3 fibers. Specifically, 3D finite-element models are used to predict the load transfer from broken to unbroken fibers as a function of applied stress and matrix yield strength. The stress concentrations around a single fiber break are then employed in a Green's function model that predicts the evolution of multiple fiber damage under increasing applied load up to failure in moderate-sized composites. These studies explicitly demonstrate the local critical damage level that must be attained to drive global failure. Analytic models for scaling of the tensile strength to large sizes typical of test coupons and components are then employed. The general method is applied to predict failure in an aluminium matrix reinforced with Al 2O 3 fibers. Good agreement at small composite sizes is obtained, but the scaling of strength with size is weaker than is observed in experiments. Possible reasons for these deviations are discussed, focusing on the appropriate constitutive response for highly constrained metal yielding at small scales. The analytic models for strength also provide information on reliability versus size and are usable in stochastic finite element models. The overall multiscale model can guide the choice of damage metrics and instability points within macroscale damage mechanics models.

Multiscale damage modelling for composite materials: theory and computational framework

AbstractA non‐local multiscale continuum damage model is developed for brittle composite materials. A triple‐scale asymptotic analysis is generalized to account for the damage phenomena occurring at micro‐, meso‐ and macroscales. A closed‐form expressions relating microscopic, mesoscopic and overall strains and damage is derived. The damage evolution is stated on the smallest scale of interest and non‐local weighted phase average fields over micro‐ and mesophases are introduced to alleviate the spurious mesh dependence. Numerical simulation conducted on a composite beam made of Blackglas/Nextel 2‐D weave is compared with the test data. Copyright © 2001 John Wiley & Sons, Ltd.

Multiscale modeling of radiation damage: applications to damage production by GeV proton irradiation of Cu and W, and pulsed irradiation effects in Cu and Fe

The damage accumulation in Cu and W is investigated using a multiscale modeling approach. The efficiency for defect production of displacement cascades is calculated using molecular dynamics (MD). The simulation uses the recoil spectra from spallation reactions of 1.1 and 1.9 GeV protons as calculated with the Los Alamos High Energy Transport (LAHET) nuclear transport code. The total number of defects produced under these irradiation conditions is obtained both from the NRT and MD approximations. The value for the change in electrical resistivity produced by the irradiation-induced defect microstructure is compared to experimental values obtained from irradiations with protons of the above energies, showing a better agreement for the lower irradiation energy. The damage evolution is simulated with kinetic Monte Carlo, where the inputs for the calculation are the results from MD previously obtained. A large recovery of the damage is found at room temperature as a result of the migration of interstitial clusters, single vacancies and small vacancy clusters to sinks such as dislocations. Finally the effects of pulsed irradiation have been analyzed in Cu and Fe with similar simulation tools. The results indicate a clear influence of pulsing at 1 Hz, but not at higher frequencies.

Multiscale Modeling of Radiation Damage of Metals and SIC in Inertial Fusion Reactors

The change in SiC properties under neutron irradiation is being experimentally assessed but it is actually far from being well understood. Using Molecular Dynamics (MDCASK-DENIM/LLNL), we show the existence of recombination barriers (metastable defects), and how they affect the cascade analysis. Displacement cascades have been systematically studied and the different role of both sublattices examined. Low-temperature amorphization by damage accumulation has been successfully simulated using MD in accordance with experiments, allowing the understanding (not possible from experiments) of the atomistic sequence of damage. We are also developing new methodologies (tight binding MD) to prove the adequacy of the interatomic potential to describe energetic of configurations needed for diffusion in SiC. The neutron source from target is obtained with time resolution, together with responses after transport in the IFE reactor. The comparison of different primary knock-on atom (PKA) energy spectra from different fusion reactors is given, which is a basic information for displacement cascade analysis. Those spectra are a direct consequence of the neutron spectra in the material (depending on protection). Supported by recent work on atomistic level, the effect of pulsed irradiation was concluded. The time between pulses has a key role in the annealing process of defects. The comparison with average continuous irradiation, and the different behaviour for vacancies and interstitials, are highlighted.