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Title: High rate properties of particulate composites
Author: Trivedi, Akash
ISNI:       0000 0004 9356 7224
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2020
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The main aim of the research presented in this thesis was to better understand the high strain rate mechanical properties of particulate composites. As the mechanical response of these materials is sensitive to rate and temperature, they must be experimentally characterised at various strain rates and temperatures, interrogating their dependences. In polymer composite materials, the rate and temperature dependence originates from the polymeric binder, which motivated the starting place for this research. Preliminary modelling frameworks were developed, based on observed rate-temperature equivalence in the mechanical properties, and the time-temperature superposition principle. By suitably representing the viscoelasticity, hyperelasticity, and viscoplasticity, the modelling frameworks enabled the high rate behaviour of neoprene rubber and (plasticised) poly(vinyl chloride) to be captured. It was shown that in order to better capture the high rate response, the temperature rise from self-heating must be related to the thermal relaxation of the elastic modulus. By calibrating the model parameters with data from quasi-static experiments performed at different temperatures, the stress-strain response at high strain rates was predicted and validated with carefully conducted experiments. The insights developed from the initial modelling frameworks were used in the latter part of the project to model the behaviour of particulate composites. These composites were based on a vulcanised, natural rubber binder filled with different grades of glass microspheres. This allowed the effect of filler volume fraction and mean particle diameter to also be investigated. These materials were chosen as their varied (rubbery through to glassy) response provided an interesting challenge for its experimental characterisation under dynamic loading. The dataset generated, partly as a result of experimental technique development, enabled the resulting insights and data to be used to develop modelling frameworks allowing the high strain rate response of unfilled and filled natural rubber to be predicted above the glass transition temperature.
Supervisor: Siviour, Clive Sponsor: Air Force Office of Scientific Research
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Materials Engineering ; Constitutive modelling ; Experimental mechanics