02 Fakultät Bau- und Umweltingenieurwissenschaften
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/3
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Item Open Access A microstructurally-based, multi-scale, continuum-mechanical model of skeletal muscle tissue(2019) Bleiler, Christian; Ponte Castañeda, Pedro; Röhrle, OliverItem Open Access Continuum-mechanical modelling across scales : homogenisation methods and their application to microstructurally-based skeletal muscle modelling(Stuttgart : Institute for Modelling and Simulation of Biomechanical Systems, Chair of Continuum Biomechanics and Mechanobiology, University of Stuttgart, 2021) Bleiler, Christian; Röhrle, Oliver (Prof., PhD)A variety of materials, such as biological soft tissues, exhibit large inter- and intra-subject microstructural variations that cannot be captured with individual material tests on the macroscopic observation scale. In such scenarios, multiscale modelling approaches are used instead, which explicitly incorporate the microstructure and provide macroscopic quantities through suitable homogenisation methods. This enables the description of biological soft tissue behaviour arising from microstructural changes, for example, those caused by disease. This thesis, therefore, deals with the multiscale continuum-mechanical modelling of materials and the particular application of such methods to the description of skeletal muscle tissue. Besides a general introduction to the subject, novel analytical estimates for the effective macroscopic potential of two-phase, hyperelastic, incompressible solids are presented. These are based on the so-called tangent second-order homogenisation method and are applicable for highly nonlinear, anisotropic material behaviour at large strains. Subsequently, a novel multiscale model for skeletal muscle is presented, which describes the macroscopic behaviour of soft tissue as a direct consequence of properties at smaller scales, such as the stiffness and arrangement of individual collagen fibres. The methods and models presented in this thesis are discussed by means of representative examples, thus demonstrating their merits in comparison to alternative approaches.Item Open Access Strain measures and energies for crimped fibres and novel analytical expressions for fibre populations : ingredients for structural fibre network models(2022) Bleiler, Christian; Röhrle, OliverThis paper deals with the structural modelling of fibre networks with a focus on the description of populations of initially crimped fibres. It presents a systematic approach of introducing appropriate strain measures for single fibres based on a deformation decomposition and by transferring knowledge from the field of elastoplasticity. On this basis, for example, the often used Biot-type fibre strain measures λ-λwand λ/λw-1, with stretch λand waviness λw, are consistently assigned to different classes of material strain (“additive”) or intermediate strain (“multiplicative”) descriptions, respectively. We review in this work different fibre strain energies based on the different stain measures and present extensive comparisons on the physical implications and the results on the fibre population and network scale. These investigations also include formulations with a Hencky-type energy based on a logarithmic strain. Furthermore, we present novel analytical expressions for fibre populations that make the evaluation of integral expression superfluous and thus lead to a significant reduction in computational time.