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Metal Plasticity

 

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Several different types of forming processes are modeled and simulated at the Institute of Mechanics. In numerical simulations of deformation processes, especially in the area of sheet metal forming, purely phenomenological models are insufficient to account for the effect of strain path changes on the forming process. As a consequence new material models have to be developed, which for example consider the anisotropy development during the forming process as well as the initial anisotropy of the material. Besides sheet metal forming, also chip formation in high speed cutting as well as e.g. extrusion of aluminum alloys is modeled and simulated using complex non-phenomenological material models.

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Phase Transformations

 

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We use different approaches to model phase transformations not only in shape memory alloys, but also in TRIP steels. One of these approaches is to implement an one-dimensional, thermodynamically consistent phase-transformation model which is then embedded into a micro-sphere formulation, facilitating to simulate three-dimensional boundary value problems. Besides statitics-based phase-transformation models we also investigate relaxation-based models where the quasi-convex energy hull is approximated numerically. Further research acitivities in this field involve the coupling of phase transformations and plasticity, where we e.g. capture the change of plastic strains due to propagating phase fronts by means of plasticity inheritance laws.

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Biological tissue

 

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Biological tissues possess a pronounced composite-type multi-scale structure together with strongly anisotropic mechanical properties. A fibre-like network structure is characteristic for this kind of materials. If the tissue will be exposed to mechanical loading, an initially unstructured collagen fibre network tends to reorient with the local dominant stretch direction – it adapts according to the particular loading conditions. In general, biological tissues exhibit changes in mass, which is denoted as growth, and changes in internal structure, which is commonly referred to as remodelling. One continuum approach investigated is based on a one-dimensional micro-mechanically motivated constitutive equation – the so-called worm-like chain model. In this case, the extension of the one-dimensional constitutive law to the three-dimensional macroscopic level is performed by means of a microsphere formulation.

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Damage and failure

 

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The research regarding damage and failure deals with the influence of deformation incompatibility on the development of glide and kink bands at a crack tip and on crack opening in single crystals, the advances in non-local ductile damage and failure modeling at large deformation with applications to engineering, the simulation of ductile crack extension in metal matrix composites using damage models, the improved modeling and simulation approach for the prediction of ductile crack growth in MMC materials, the comparison of RVE and unit-cell simulations of damage and failure in particle-reinforced metal matrix composites, the application of cohesive elements for fracture simulation, the modeling the interface behaviour in MMC materials with cohesive elements, the simulation of ductile damage and fracture in MMC materials with a non local damage model, and many more topics.

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