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dc.contributor.authorVan Loock, Frederik
dc.description.abstractThis thesis contributes to the understanding of the deformation and fracture of methyl methacrylate (MMA)-based polymers in the context of void growth. The first part of the thesis focuses on the prediction of void growth during solid state nanofoaming of polymethyl methacrylate (PMMA). These predictions may contribute to the development of polymeric foams with a thermal conductivity close to that of air. The second part of the thesis explores the fracture behaviour of structural adhesive (e.g. MMA)-based joints. An adhesive layer within such a joint is prone to defects such as (micro)voids and (micro)cracks. The ability to accurately predict the failure strength of adhesive joints as a function of pore or crack size is essential in order to design reliable structures based on adhesive bonding technology. A one dimensional void growth model is developed to simulate cavity expansion during solid-state nanofoaming of PMMA by CO$_2$ in the first part of the thesis. To that end, tensile tests on two PMMA grades of markedly different molecular weight are conducted close to the glass transition temperature and over two decades of strain rate. The void growth model makes use of fitted constitutive laws for each PMMA grade and the effect of dissolved CO$_2$ is accounted for by a shift in the glass transition temperature of the PMMA. Solid-state nanofoaming experiments are performed on the two PMMA grades to validate the void growth model. The morphology of the foams (and the limit in attainable porosity) is found to be sensitive to the molecular weight. The measured porosity versus foaming time curves are in good agreement with those predicted by the model, for porosities below the maximum observed porosity. The observed limit of achievable porosity is interpreted in terms of cell wall tearing; it is deduced that the failure criterion is sensitive to cell wall thickness. The tensile strength of a centre-cracked elastic layer, sandwiched between two elastic substrates, and subjected to remote tensile stress, is predicted in the second part of the thesis. An analytical theory is developed by making use of a cohesive zone at the crack tip to predict the strength of the joint as a function of the relative magnitude of crack length, layer thickness, plastic zone size, specimen width, and elastic modulus mismatch ratio. Joint design maps are constructed, revealing competing regimes of fracture. The analytical theory is verified by finite element calculations, and validated by means of two experimental case studies.
dc.description.sponsorshipEPSRC, SABIC
dc.rightsAttribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)
dc.subjectPolymethyl methacrylate
dc.subjectDeformation maps
dc.subjectFailure maps
dc.subjectTensile tests
dc.subjectSolid-state foaming
dc.subjectGas dissolution foaming
dc.subjectMolecular weight
dc.subjectVoid growth model
dc.subjectCavity expansion
dc.subjectAdhesive joint
dc.subjectFinite element analysis
dc.subjectCohesive zone
dc.subjectStiffness mismatch
dc.subjectCellulose acetate
dc.titleDeformation and fracture of PMMA with application to nanofoaming and adhesive joints
dc.type.qualificationnameDoctor of Philosophy (PhD)
dc.publisher.institutionUniversity of Cambridge
dc.contributor.orcidVan Loock, Frederik [0000-0003-0581-2238]
dc.type.qualificationtitlePhD in Engineering
cam.supervisorFleck, Norman
cam.supervisor.orcidFleck, Norman [0000-0003-0224-1804]

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Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)
Except where otherwise noted, this item's licence is described as Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)