This is the author’s version of a work that was accepted for publication in the journal, International Journal of Plasticity. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published at: http://dx.doi.org/10.1016/j.ijplas.2011.07.003Discrete dislocation dynamics (DDD) has been used to model the deformation of nickelbased\ud single crystal superalloys with a high volume fraction of precipitates at high temperature.\ud A representative volume cell (RVC), comprising of both the precipitate and the\ud matrix phase, was employed in the simulation where a periodic boundary condition was\ud applied. The dislocation Frank–Read sources were randomly assigned with an initial density\ud on the 12 octahedral slip systems in the matrix channel. Precipitate shearing by superdislocations\ud was modelled using a back force model, and the coherency stress was\ud considered by applying an initial internal stress field. Strain-controlled loading was applied\ud to the RVC in the [0 0 1] direction. In addition to dislocation structure and density evolution,\ud global stress–strain responses were also modelled considering the influence of precipitate\ud shearing, precipitate morphology, internal microstructure scale (channel width and\ud precipitate size) and coherency stress. A three-stage stress–strain response observed in\ud the experiments was modelled when precipitate shearing by superdislocations was considered.\ud The polarised dislocation structure deposited on the precipitate/matrix interface was\ud found to be the dominant strain hardening mechanism. Internal microstructure size, precipitate\ud shape and arrangement can significantly affect the deformation of the single crystal\ud superalloy by changing the constraint effect and dislocation mobility. The coherency\ud stress field has a negligible influence on the stress–strain response, at least for cuboidal\ud precipitates considered in the simulation. Preliminary work was also carried out to simulate\ud the cyclic deformation in a single crystal Ni-based superalloy using the DDD model,\ud although no cyclic hardening or softening was captured due to the lack of precipitate\ud shearing and dislocation cross slip for the applied strain considered

This article was published in the journal, Engineering Fracture Mechanics [© Elsevier] and the definitive version is available at: http://dx.doi.org/10.1016/j.engfracmech.2011.04.006Crystalplasticity has been applied to model the cyclicconstitutive behaviour of a polycrystalline nickel-based superalloy at elevated temperature using finite element analyses. A representative volume element, consisting of randomly oriented grains, was considered for the finite element analyses under periodic boundary constraints. Strain-controlled cyclic test data at 650 °C were used to determine the model parameters from a fitting process, where three loading rates were considered. Model simulations are in good agreement with the experimental results for stress–strain loops, cyclic hardening behaviour and stress relaxation behaviour. Stress and strain distributions within the representative volume element are of heterogeneous nature due to the orientation mismatch between neighbouring grains. Stress concentrations tend to occur within “hard” grains while strain concentrations tend to locate within “soft” grains, depending on the orientation of grains with respect to the loading direction. The model was further applied to study the near-tip deformation of a transgranular crack in a compact tension specimen using a submodelling technique. Grain microstructure is shown to have an influence on the von Mises stress distribution near the crack tip, and the gain texture heterogeneity disturbs the well-known butterfly shape obtained from the viscoplasticity analysis at continuum level. The stress–strain response near the crack tip, as well as the accumulated shear deformation along slip system, is influenced by the orientation of the grain at the crack tip, which might dictate the subsequent crack growth through grains. Individual slip systems near the crack tip tend to have different amounts of accumulated shear deformation, which was utilised as a criterion to predict the crack growth path

This article was published in the journal, Materials Science and Engineering: A [© Elsevier] and the definitive version is available at: http://dx.doi.org/10.1016/j.msea.2010.02.045Cyclic deformation at elevated temperature has been modeled for a polycrystalline nickel-based superalloy using the crystal-plasticity constitutive formulations. Finite element analyses were carried out for a representative volume element (RVE), consisting of randomly oriented grains and subjected to periodic boundary constraints. Model parameters were determined by fitting the strain-controlled cyclic test data at 650 °C for three different loading rates. Simulated results are in good agreement with the experimental data for both stress–strain loops and cyclic hardening behavior. The model was utilized to predict the stress relaxation behavior during the hold periods at the maximum and minimum strain levels, and the prediction compares well with the experimental results. Localized stress and strain concentrations were observed due to the heterogeneous nature of grain microstructure and the mismatch of the mechanical properties of individual grains

This is an open access article under the CC BY license (http://\ud creativecommons.org/licenses/by/4.0/).Using crystal plasticity, finite element analyses were carried out to model cyclic deformation for a low\ud solvus high refractory (LSHR) nickel superalloy at elevated temperature. The analyses were implemented\ud using a representative volume element (RVE), consisting of realistic microstructure obtained from SEM\ud images of the material. Monotonic, stress-relaxation and cyclic test data at 725 C were used to determine\ud the model parameters from a fitting process and their sensitivity to RVE size and random grain orientation.\ud In combination with extended finite element method (XFEM), the crystal plasticity model was further\ud applied to predict surface crack growth, for which accumulated plastic strain was used as a fracture\ud criterion. Again, realistic microstructure, taken from the cracking site on the surface of a plain fatigue\ud specimen, was used to create the finite element model for crack growth analyses. The prediction was conducted\ud for a pseudo-3D geometrical model, resembling the plane stress condition at specimen surface.\ud The loading level at the cracking site was determined from a viscoplasticity finite element analysis of\ud the fatigue specimen. The proposed model is capable of predicting the variation in growth rate in grains\ud with different orientations