Vibrations of a flexible membrane coupled to a liquid material sample during its phase transition to solid: modelling, validation and identification****

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Material characterization is primordial for R&D, manufacturing processes and quality control, in particular for soft viscoelastic materials in agri-food - dairy - and life sciences industries. However, the classical methods to identify their bulk properties, such as rheometers, are mainly destructive, needing many different samples to test a material at different stages, resulting in a loss of statistical strength. Such issues are solved by a wave-propagation method inspired by medical dynamic elastography and developed by the Canadian company Rheolution as an at-line compatible technique to measure, without any prior knowledge, viscoelastic properties of soft solid materials. This patented technology consists in measuring the free response to a vibrational impulse of a bi-layered system comprised of a material specimen and of a flexible membrane, bottom of a solid cylinder sample holder. Its response is compared to the simulation of a model in which the only unknowns are the specimen's viscoelastic parameters, allowing their identification thanks to an error minimization procedure. However, this model fails to reproduce the response for extremely soft solids and for materials transitioning between liquid and solid states, significant in Rheolution's targeted markets. Therefore, this project aims at developing a model of this bi-layered system's behavior for such samples. Experiments will be conducted to comprehend the system's vibrational response with such specimens and to optimize its design. The specimen's viscoelastic or rheological behavior, its interaction with the solid sample holder and its influence on the membrane's vibrations, will be derived and linked to the existing theory for soft solid materials to obtain a generalized model of this system to be validated with experimental data. Then, algorithms will be formulated to identify the sample's viscoelastic parameters and applied on typical materials. This extended technique will improve the yield of Canadian dairy industry production lines - allowing for more ecological and cost-effective production - and will help simple, cheaper and more accurate characterization of biomaterials gelation or degradation, for drug delivery or tissue regeneration, and thereby enhancing Canadians' health.**************************