Browsing by Author "Du Toit, Viljoen"
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- ItemCharacterising material models for silicone-rubber using an inverse finite element model updating method(Stellenbosch : Stellenbosch University, 2018-03) Du Toit, Viljoen; Venter, Gerhard; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.ENGLISH ABSTRACT: Silicone-rubber was investigated and its mechanical behaviour was characterised. Uni-axial tensile tests were conducted on two different sample geometries: rectangular flat strip and dumbbell shaped. Bi-axial bubble inflation tests were done on membranes and unconstrained uni-axial compression tests were conducted on cylindrical samples. Two identification methods were incorporated to determine three constitutive hyper-elastic material models from every experimental test: the direct and inverse. The direct method is the more traditional approach, where experimental data is used with a least squares fit to determine the constants that govern the material model. The inverse method is fundamentally different, it requires a finite element (FE) model and experimental results. The experimental results are used as boundary conditions in the FE model. Numerical optimisation is then used to obtain the material model constants that minimise the error between the FE model and the experimental results. The material models investigated in this thesis include the Mooney-Rivlin two- and three parameter models along with the Ogden three parameter model. Finally, an independent validation test was done, with a complex stress state. The validation test along with the extrapolation of each material model into all three stress states (uni-axial tension, -compression and bi-axial tension), served as the criteria to determine the best material model and identification method. It was found that the Mooney-Rivlin three parameter model obtained from uni-axial tensile tests (both sample geometries) using both the direct and inverse FE model updating method delivered the best results. However, additional user-input constraints were needed for the direct method (inverse method required no constraints) to obtain a material model that predicted feasible material behaviour.