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Title: Investigating the effect of mesostructure on the shock response of granular materials through numerical modelling
Author: Derrick, James
ISNI:       0000 0004 7658 8648
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2019
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Shock compaction of granular matter is of great interest to many fields such as planetary science, shock-chemistry, and ballistics. Often, in planetary science particularly, the scales are too large to perform experiments. Models are needed that parametrise the porosity. These are developed by investigating the response of granular systems whilst controlling influential properties. Granular matter, however, possesses many potentially influential properties and numerical models are the best method available to investigate granular matter whilst controlling its many properties. This thesis considers the effects of mesostructure on the shock response of granular matter. The number of contacts present in a granular system has a distinct effect on its shock response and it is observed that more contacts can artificially stiffen a granular material's shock response. The shock compaction of a bimodal powder, is an important problem in recent research into the formation of asteroids. A joint numerical-experimental approach was taken to investigate shock response in this system at the mesoscale. The large grains, embedded in the fine surrounding powder were found to 'shield' the fine powder as the shock wave passed. The porosity vector was introduced to quantify this effect. Finally, the thesis examines the efficacy of semi-explicitly resolving more complex granular materials in simulations, with the lunar regolith as a case study. The method was found to reproduce an explicitly resolved sample's response best when the parametrised material was engineered to possess the same porosity as the bulk porosity (through introduction of explicit pore space). Changing the grain morphology did not affect the system on the bulk scale, but local changes were observed and a critical angle a grain face could have with a shock wave was found that generated the highest local temperatures and pressures.
Supervisor: Collins, Gareth Sponsor: Consejo Nacional de Ciencia y Tecnología ; Engineering and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral