Modelling and characterisation of porous materials

[摘要] Porous materials possessing random microstructures exist in both organic (e.g.polymer foam, bone) and in-organic (e.g. silica aerogels) forms. Foams andaerogels are two such materials with numerous engineering and scientificapplications such as light-weight cores in sandwich structures, packaging, impactand crash structures, filters, catalysts and thermal and electrical insulators. Assuch, design and manufacture using these materials is an important task that canbenefit significantly from the use of computer aided engineering tools. With theincrease in computational power, multi-scale modelling is fast becoming apowerful and increasingly relevant computational technique. Ultimately, the aim isto employ this technique to decrease the time and cost of experimentalmechanical characterisation and also to optimise material microstructures. Boththese goals can be achieved through the use of multi-scale modelling to predictthe macro-mechanical behaviour of porous materials from their microstructuralmorphologies, and the constituent materials from which they are made. The aim ofthis work is to create novel software capable of generating realistic randomlymicro-structured material models, for convenient import into commercial finiteelement software. An important aspect is computational efficiency and alltechniques are developed paying close attention to the computation time requiredby the final finite element simulations. Existing methods are reviewed and whererequired, new techniques are devised. The research extensively employs theconcept of the Representative Volume Element (RVE), and a Periodic BoundaryCondition (PBC) is used in conjunction with the RVEs to obtain a volume-averagedmechanical response of the bulk material from the micro-scale. Numericalmethods such as Voronoi, Voronoi-Laguerre and Diffusion Limited Cluster-ClusterAggregation are all employed in generating the microstructures, and wherenecessary, enhanced in order to create a wide variety of realistic microstructuralmorphologies, including mono-disperse, polydisperse and isotropic microstructures(relevant to gas-expanded foam materials) as well as diffusion-basedmicrostructures (relevant for aerogels). Methods of performing large strainsimulations of foams microstructures, up to and beyond the onset strain of densification are developed and the dependence of mechanical response on thesize of an RVE is considered. Both mechanical and morphological analysis of theRVEs is performed in order to investigate the relationship between mechanicalresponse and internal microstructural morphology of the RVE. The majority of theinvestigation is limited to 2-d models though the work culminates in extending themethods to consider 3-d microstructures.

[发布机构] University:University of Glasgow;Department:School of Engineering

[关键词] TJ Mechanical engineering and machinery