Browsing by Author "Franciena Helena"
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- ItemInvestigating an inverse finite element approach for characterising soft materials(Stellenbosch : stellenbosch University, 2020-04) Franciena Helena; Muller, Jacobus Hendrik; Venter, Gerhard; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.ENGLISH ABSTRACT: Micro-indentation was investigated as a method for characterising soft materials. This research characterised a soft silicone rubber using an inverse finite element (FE) approach with six different indentation tests. Four tests consisted of a cylindrical indenter, with the variability factors being the number of indenters and orientation of the indenter. Two tests consisted of a spherical indenter, with the difference between the tests being the number of indenters used. Each indentation test consisted of two FE models, one containing a known MooneyRivlin three parameter material model and one which needed characterisation. MSC Marc Mentat (2019) was used to perform all FE analysis. The remeshing feature within Marc was implemented within the FE analysis to minimise the element distortion present when deforming a non-linear material to a complex deformation field. Python was used to develop a numerical pipeline, which controlled and linked the different software and procedures. Two optimisation algorithms were investigated, Sequential Quadratic Programming (SQP) and Sequential Linear Programming (SLP). Radial Basis Functions (RBF) were used to interpolate the FE analysis results. The root mean square (RMS) error of the displacement fields, was minimised as objective function within the optimisation procedure. It was found that one cylindrical indenter, applied in a diagonal orientation across a square test sample, obtained the best material model using the SQP optimisation algorithm. From the observations within the results, it was concluded that a material model either matched the displacement field or the engineering vs. stretch nearly perfectly, but not both simultaneously.