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Multiscale Analysis of Thermomechanical Behaviour of Granular Materials

Periodic Reporting for period 1 - MatheGram (Multiscale Analysis of Thermomechanical Behaviour of Granular Materials)

Reporting period: 2019-01-01 to 2020-12-31

Granular materials, such as soils, agricultural seeds, metallic and ceramic powders and pharmaceutical powders, are ubiquitous in nature and have many industrial applications. They possess unique physical properties and a complicated flow behaviour, which is determined both by interactions between the particles and by interactions with the surrounding media (i.e. liquids or gases). Depending on their stress states and density, granular materials can behave both liquid- or solid-like. Although extensive research has been devoted to understanding their complex behaviour and how to process and use these materials, our understanding of the thermomechanical behaviour of granular materials remains very limited, particularly in the following three areas:
1) How temperature increases within granular materials without the application of external heating sources, as a result of friction, particle deformation or particle-particle reactions, and then transfers among the granular materials — heat generation and transfer. Previous studies have primarily focused on heat transfer between granular materials and surrounding media;
2) How the accumulation of heat and subsequent temperature rise affect the physical properties of granular materials — thermal effects. Previous studies have often assumed that physical properties such as microstructure, flow and mechanical properties are temperature-independent and have ignored the fact that most of these properties are temperature-dependent;
3) How the thermomechanical attributes of granular materials can be effectively utilised in emerging applications, e.g. additive manufacturing, powder coating, heat regulation/insulation, and catalysis — processing and applications.

While PhD research in granular materials has clear potential in industrial applications in a range of sectors, much of the traditional research training that takes place in universities occurs without commercial and industrial context in a single scientific discipline and without due consideration of gender balance; so early stage researchers, in particular female ones, can miss out on the opportunity to gain insights into solving industrial challenges. This narrowness of exposure leads to researchers thinking of a future career either only in academia or only in the industrial sector that is most closely related to their PhD projects. Moreover, the lack of gender balance in conventional PhD training results in many talented female researchers missing their opportunities to embark on a science and technology career in such a fascinating field.

In order to address these challenges, the overall objectives of MATHEGRAM are 1) to perform a concerted and systematic programme of multidisciplinary research training in order to thoroughly understand the thermomechanical behaviour of granular materials and hence determine the more efficient use of these materials in different industrial sectors, e.g. through more realistic modelling and thorough experimental validation; and 2) to train the next generation of professional engineers/scientists.
During the 1st reporting period, we have recruited 14 ESRs who have been undertaking essential training as well as the planned individual research projects. We re-prioritised the running order of the network training events and held one Advanced Training Course on “Modelling and characterisation of granular materials” that provided the essential research skills for ESRs to start their individual research projects, and one Training School on “Research methods, and science communications” that equipped ESRs with essential transferable skills. Albeit the severe disruption caused by COVID-19, ESRS have made very impressive progress on their research projects. In particular, several discrete element models (DEM) were developed that dramatically enhance the DEM capacity for analysing thermomechanical behaviour of granular materials. Furthermore, several experimental systems have been developed and upgraded to enable detailed investigation of micromechanics and macroscopic behaviour of granular materials during various applications and processes. These results have been disseminated through journal publications, conference proceedings and MATHEGRAM newsletters. In addition, we are holding monthly virtual seminars to disseminate our research to a much wider community, which are extensively promoted using social media (Twitter and LinkedIn), as well as personal contacts.
It is expected the developed DEM for heat generation induced by internal friction, plastic deformation and chemical reaction, for heat transfer due to conduction, convection and radiation, and with consideration of thermo-mechanical behaviour of granular materials will be thoroughly validated. The advanced DEM can be used by other researchers to explore the complicated behaviour of granular materials impacted by heat generation and temperatures for a wide range of applications. The use of in situ nano-computed tomography (nano-CT) to understand the microscopic evolution of a granular material at high temperatures even with the interaction of a liquid phase originated from the melt component during sintering, i.e. to elucidate the micromechanics of constrained sintering and capillary-induced sintering enables a ‘real’ compact made from ceramic particles of a few microns to be observed, rather than just the reorientation of large metallic particles (~200μm) that has hitherto been possible. A systematic approach will be taken to examine the effects of temperature on mechanical properties, micromechanics, flow, compaction and mechanical properties, to enhance our understanding of the thermal performance of granular materials and broaden their industrial applications. The application of dry powder coating in aerospace applications will be explored and evaluated, appropriate materials and manufacturing processes will be developed to enhance the application of granular materials in the aerospace industry, which has the potential to revolutionise the conventional coating processes currently employed in the aerospace industry. The modelling and experimental capabilities developed will enable wider application in various industries to reduce the cost and waste so the manufacturing processes can be made greener and cheaper.
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