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Solid Mechanics & Materials Engineering Group |
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Solid Mechanics and Materials
Engineering Group Seminars
Michaelmas 2009
For further information, contact Clive Siviour, Telephone
01865 (2)83473
Dr Kostas Danas, University of Cambridge In this talk, we employ discrete dislocation models and strain-gradient plasticity theories to investigate size effects in plasticity at micron scales. The talk will be divided in two main sections. In the first section, we investigate the role of interfaces in the elastic-plastic response of a sheared single crystal making use of discrete dislocation dynamics and strain gradient crystal plasticity theories. More specifically, the upper and lower faces of a single crystal are bonded to rigid adherends via interfaces of finite thickness. The sandwich system is subjected to simple shear, and the effect of the compliance of crystal layer and of interfaces upon the overall response are explored. In the second part of the talk, we implement the tensorial strain gradient plasticity theory of Fleck and Willis (2009b) (see also Gudmundson (2004)) in a fixed finite element framework in order to predict indentation hardness. Three length scale parameters are introduced and a fairly general investigation of the role of these parameters on the indentation hardness is carried out. The resulting hardness trends are also explored in the context of hardening materials. Finally, other models proposed in the literature (such as spherical void expansion and Nix and Gao (1998) model) are evaluated by making use of the current strain gradient formulation.
Within the framework of the linear theory of elasticity, the heterogeneous problem associated with multiple inclusions in an infinite matrix (or in a half-plane matrix and in a strip), circularly cylindrical layered media and plane layered media is considered and solved. The number of inclusions and layers is arbitrary and the system is subjected to arbitrary loading including singularities such as dislocations, concentrated forces. The solutions to the heterogeneous problem are derived by the heterogenization technique which allows us to write down the solution explicitly in terms of the solution of a corresponding homogeneous problem subjected to the same loading. A rapid convergent series solution is expressed in terms of an explicit general term of the complex potential of the corresponding homogeneous problem in an elegant form. Numerical results are provided for some particular examples to investigate the effect of loading conditions, material combinations and geometrical configurations on the interfacial stresses. Keywords: Heterogenization, dislocations, interfacial stresses Professor Carlo Sansour, University of Nottingham Prashant Potnis, University of Oxford XRD, SEM and AFM study of ferroelectric microstructure Ferroelectric ceramics are widely used for industrial applications such as sensors and actuators where higher strain output is desirable. Single crystal ferroelectrics show far greater strains than the conventional polycrystalline ceramics but still are not used widely in industrial applications. One of the main reasons is lack of understanding of the microstructure evolution in these crystals. In this talk, various techniques used for studying the microstructure will be explored. Domain structure in single crystals of Barium Titanate is observed by reflection topography using synchrotron X-ray light. Interpretation of the microstructure is confirmed by optical microscopy, SEM and AFM of etched crystals. The results will be presented along with the importance of each technique in revealing distinct useful information about the domain structure. Finally, evolution of needle-type microstructure in these crystals under compressive load will be discussed in brief. Professor Marc A Meyers, University of California Laser Compression and Fragmentation of Metals Using the Janus LLNL and Omega facilities, we are using laser energy to generate shock and quasi-isentropic compression of monocrystalline, polycrystalline and nanocrystalline FCC and BCC metallic specimens (Cu, Ni, V). We have investigated the internal defects generated by experimental and computational (MD) means. By comparing experimentally observed and computationally predicted structures we can obtain new insights into the fundamental deformation mechanisms. We have also investigated the mechanisms of spall initiation, propagation, and fragmentation. Robert Gerlach,
University of Oxford
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