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Modelling, Simulation of Visco-Elastic Plastic Behaviour for Soft-Solids by CONE Indenters

Dr. Dharmendra C. KOTHARI, Prof. Paul F. LUCKHAM

Materials deforms in response to an externally applied stress. The deformation can be permanent or temporary. Permanent deformation stays after the removal of the applied stress, while temporary deformation disappears on the removal of the stress. Both temporary and permanent deformations can be functions of time or virtually independent of time. Processing and handling of intermediate or final products involving particulate materials dispersed in liquid media at high solids volume fraction means Soft-Solids, present major challenges in the chemical industry and in its allied sections, such as; Biochemical and Biotechnology apparently the drugs and Pharmaceuticals industries. In the development of new processes, manufactures are faced with growing diversity of equipment options and a limited technical basis for selection, of their complex flow behaviour and the influence of the wall boundary conditions. Pilot scale trials may be lengthy, expensive and has to rely on uncertain rules of modelling scale-up. Therefore the current strategy which is emerging world-wide is to employ computer simulation as a basis for optimising the design and operating parameters. Importantly, soft-solids exhibit complex bulk flow and interfacial properties; that leads to the requirement for accurate and reliable constitutive information to model their processing. To obtain useful experimental data, there is a need for a well characterised and reproducible material. The „BEST‟ material will undergo sufficient plastic flow so as to be capable of being formed. Therefore a model paste Plasticine for Simulation and Terracotta for Modelling has been tested by CONE indenter over a wide range of strain rates. It was found that the terracotta exhibits a linear elastic behaviour at low stress levels and power law creeping behaviour at higher levels of stress. All the loading and relaxation tests at various strain-rates give the same material properties. This means that the model works reasonably well. The analysis of loading and relaxation is simple robust and easily provides a value of E, and the flow curve, this is also true for CONE indentation of soft-solids. The primary aim of this project was to attempt for developing and evaluating codes of the Finite Element Analysis (FEA) which are specifically designed for paste system. The finite element method has been shown to be viable computational tool for modelling pastes and the effects of the friction. However the practicality of the data method is very much dependent upon the accurate modelling of the paste behaviour. The predicted results, in some cases, show a reasonable agreement with those obtained experimentally.