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Computational Modelling of Mechanical Behaviour of "Elastomer-Steel Fibre" Composite
Lasota, Tomáš ; Okrouhlík,, Miloslav (oponent) ; Nováček,, Vít (oponent) ; Burša, Jiří (vedoucí práce)
This thesis deals with composite materials made of elastomer matrix and steel reinforcement fibres with various declinations. It presents computational simulations of their mechanical tests in uniaxial tension and three-point bending realized using finite element (FE) method, and their experimental verification. The simulations were carried out using two different models - bimaterial and unimaterial computational models. The bimaterial model reflects structure of the composite in detail, i.e. it works with the matrix and individual fibres. When the bimaterial model is used, then it is necessary to create each fibre of the composite in the model and it makes numbers of disadvantages (creation of the model is laborious, higher number of elements are needed for discretization of an individual fibre in FE softwares and computational time is higher). On the other side, the unimaterial model does not distinguish the individual fibres, but it works with a model of the whole composite as a homogeneous material and the reinforcing effect of the fibres is included in the strain energy density function. Comparison between experiments and simulations shows that the bimaterial model is in good agreement with the experiments unlike the unimaterial one being able to provide adequate results in the case of tension load only. Hence, a new way was sought of how to extend the unimaterial model by the bending stiffness of fibres. In 2007 Spencer and Soldatos published a new extended unimaterial model that is able to work with both tension and bending stiffnesses of fibres. However, their model is based on Cosserat continuum theory, it is very complicated and is not suitable for practical application. Hence, a new simplified model was created in the thesis (partially according to the Spencer and Soldatos) with own strain energy density function proposed. In order to verify the new unimaterial model with bending stiffness, all the needed equations were derived and a new own finite element solver was written. This solver is based on Cosserat continuum theory and contains the mentioned anisotropic hyperelastic unimaterial model with bending stiffness. It was necessary to use the so called C1 elements, since the Cosserat theory works with second derivatives of displacements. The C1 elements ensure continuity of both displacements field and their first derivatives. Finally, new simulations were performed using the created FE solver and they show that the bending stiffness of fibres can be driven by the appropriate material parameter. In conclusion of this work it is discussed whether the new unimaterial model with bending stiffness is able to provide the same results as the bimaterial model, namely for both tension and bending loads of a composite specimen.
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