Multi-scale computational-experimental analysis of the mechanics of interfaces

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• Prof Marc Geers, TU Eindhoven
• Friday 10 February 2012, 14:00-15:00
• Department of Engineering - LR6.

If you have a question about this talk, please contact Anna Walczyk.

Interfaces are omnipresent in most engineering materials and structures across the scales, and they have a major impact on the resulting mechanical properties, both in the positive and the negative sense. Considerable research efforts are nowadays focused on the adequate computational description of the interface, which has to account for its different constitutive behaviour modes at each of the scales. At the level of micro-scale deformation mechanisms these modes typically are: constraining deformation (hard surface coatings, interfaces in precipitation strengthened alloys), absorbing deformation (decohesion and delamination), transmitting deformation (plastic slip through grain boundaries). The role of external and internal boundaries is even more dominant in micromechanical systems, where the surface-to-volume ratio changes drastically. Ample research efforts are being initiated in the field to reveal the mechanical behaviour of interfaces and surfaces across the scales, whereby the experimental analysis and the computational modelling thereof is a prime goal. This presentation addresses trends and challenges in the computational-experimental analysis of the mechanics of interfaces, from different perspectives: -Cohesive interfaces: Cohesive zones are by now a classical tool to describe one of the particular behaviour modes of interfaces, dominated by decohesion and delamination. In the context of this wide spread field of interface mechanics, emphasis is put on a few particular issues: – Large deformation aspects – Numerical-experimental identification of cohesive zone parameters – Quasi-brittle interfaces, involving an extreme discretization sensitivity - Intrinsic multi-scale aspects: The cohesive zone concept lumps all deformation in the interfacial decohesion plane. The limitations thereof are not always properly understood, and will be illustrated with a particular example. These limitations call for an extended interfacial description, in which novel multi-scale methods play an important role. Multi-scale characterization of delaminating polymer-metal interfaces [image] - Constraining interfaces: Compatible interfaces will naturally induce a constraint through the coarse-scale elastic fields. Less obvious are the resulting constraints acting on the microscale carriers of deformation and the resulting coarse grained impact thereof. This holds particularly for plastic slip in metals, as occurring at grain boundaries, phase boundaries, oxide layers, coatings, etc. This problem reveals the intrinsic role of discreteness and shows a rigorous link with strain gradient plasticity models, whereby its physical justification becomes more natural. - Transmitting interfaces: In some particular cases, fine scale deformation carriers are able to cross the interface. This is particularly relevant for interfaces joining materials with similar atomic or microstructures and similar deformation carriers, e.g. dislocation-based slip in single phase or multi-phase polycrystals. A simple grain boundary is the most typical example, and proper constitutive equations to describe the physical phenomena accurately are still lacking. - Size effects resulting from interfaces and surfaces: Interfaces and boundaries in microelectronics and miniaturized systems are intrinsically important, for which the typical size of the material’s microstructure is no longer negligible with respect to the component or structural size. As a result, characteristic size effects emerge.

This talk is part of the Engineering - Mechanics Colloquia Research Seminars series.

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