@article {1666, title = {Kink band and shear band localization in anisotropic perfectly plastic solids}, journal = {Journal of the Mechanics and Physics of Solids}, volume = {146}, year = {2021}, pages = {104183}, abstract = {

Shear-driven strain localization has been observed in a wide variety of materials and may take the form of shear bands or kink bands. Based on observations of kink bands in plastically anisotropic metallic nanolaminates and single crystal metals, we posit that, for the specific case of isochoric deformation, the kinematics of kink band formation are indistinguishable from those of plane strain shear band formation. The only distinction between shear bands and kink bands in these systems would then be that kink bands \‘lock up\&$\#$39; at a particular value of material rotation while shear bands may progress to arbitrarily high strains. In order to investigate whether strong material anisotropy is sufficient to arrest shear localization at a geometry that matches the classic kink band geometry, we model the development of a band of simple shear within an anisotropic perfectly plastic material. The resulting analytical model provides the stress state needed to maintain the kinematics of simple shear as a function of material anisotropy, deformation band orientation, and shear strain (or equivalently, material rotation). It is found that plastic anisotropy can promote either kink band or shear band formation depending on the loading orientation. When the deviatoric stress is positive parallel to the plane of anisotropy, shear localization may progress without bound and a shear band is produced. When the deviatoric stress is negative parallel to the plane of anisotropy, shear localization is arrested after a certain material rotation, resulting in a kink band. Examination of the requisite applied stress state during kink band formation provides an explanation for the experimentally-observed \‘lock up\&$\#$39; geometry. Solutions for the band boundary inclination angle are obtained and used to provide bounds on permissible band angles for both shear bands and kink bands.

}, keywords = {Anisotropic material (B), Ideally plastic material (B), Layered material (B), Shear localization}, issn = {00225096}, doi = {10.1016/j.jmps.2020.104183}, url = {https://doi.org/10.1016/j.jmps.2020.104183}, author = {Nizolek, Thomas J. and Pollock, Tresa M. and Mcmeeking, Robert M.} } @article {1396, title = {Creep resistance of bulk copper{\textendash}niobium composites: An inverse effect of multilayer length scale}, journal = {Acta Materialia}, volume = {176}, year = {2019}, pages = {189{\textendash}198}, abstract = {

Metallic multilayer systems show promising performance in extreme environments, with high stability of bi-metal interfaces down to nanometer length scales. The creep behavior of bulk, accumulative roll bonded (ARB) Copper\–Niobium (Cu\–Nb) composites has been studied at 400 \°C as a function of layer thickness, ranging from 2 \μm to 65 nm. Similar to single phase metallic systems, three regimes are observed during creep: transient, steady-state and tertiary. The mechanism controlling minimum creep rate for all conditions tested has a strong dependence on stress, consistent with dislocation-dominated creep. Unlike the conventional effect of grain size on creep resistance, this study reveals that decreasing length scale increases creep resistance.

}, keywords = {Creep, Cu-Nb, Length scale, Multilayer}, issn = {13596454}, doi = {10.1016/j.actamat.2019.06.029}, url = {https://doi.org/10.1016/j.actamat.2019.06.029}, author = {Avallone, Jaclyn T. and Nizolek, Thomas J. and Bales, Benjamin B. and Pollock, Tresa M.} } @article {1381, title = {A model for high temperature deformation of nanolaminate Cu-Nb composites}, journal = {Materials Science and Engineering A}, volume = {761}, year = {2019}, pages = {138016}, abstract = {

Nanolaminate composites with layer thicknesses down to 65 nm display conventional 3 stage creep behavior with creep resistance increasing as layer thickness decreases. A model for the time dependent high temperature deformation response of Cu-Nb composites is developed, and compared to creep tests performed on multilayers fabricated via accumulative roll bonding (ARB). The model assumes a continuous laminate structure of 50\% Cu and 50\% Nb in which deformation is controlled by stage II creep for the copper (\ε˙cr=A\σn) and plasticity in Nb. Regimes in which composite steady-state creep at constant stress can be achieved are identified. The modeling illustrates that strain-hardening in the niobium plays a critical role in the transient response of the multilayer, which can dominate the creep lifetime. The combination of experiments and models strongly suggest that dislocation climb mechanisms in the copper control the time-response at 400 oC for all layer thicknesses tested.

}, keywords = {Creep model, Cu-Nb, Multilayer composite, Strain hardening}, issn = {09215093}, doi = {10.1016/j.msea.2019.06.026}, url = {https://doi.org/10.1016/j.msea.2019.06.026}, author = {Avallone, Jaclyn T. and Nizolek, Thomas J. and Pollock, Tresa M. and Begley, Matthew R.} }