dc.contributor.author Van Loock, Frederik dc.date.accessioned 2019-07-19T09:25:33Z dc.date.available 2019-07-19T09:25:33Z dc.date.issued 2019-10-26 dc.date.submitted 2019-04-11 dc.identifier.uri https://www.repository.cam.ac.uk/handle/1810/294793 dc.description.abstract This 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.sponsorship EPSRC, SABIC dc.language.iso en dc.rights Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0) dc.rights.uri https://creativecommons.org/licenses/by-nc-nd/4.0/ dc.subject Polymethyl methacrylate dc.subject Nanofoams dc.subject Deformation maps dc.subject Failure maps dc.subject Tensile tests dc.subject Solid-state foaming dc.subject Gas dissolution foaming dc.subject Molecular weight dc.subject Void growth model dc.subject Cavity expansion dc.subject Adhesive joint dc.subject Finite element analysis dc.subject LEFM dc.subject Cohesive zone dc.subject Stiffness mismatch dc.subject Cellulose acetate dc.title Deformation and fracture of PMMA with application to nanofoaming and adhesive joints dc.type Thesis dc.type.qualificationlevel Doctoral dc.type.qualificationname Doctor of Philosophy (PhD) dc.publisher.institution University of Cambridge dc.publisher.department Engineering dc.date.updated 2019-07-19T07:40:09Z dc.identifier.doi 10.17863/CAM.41889 dc.contributor.orcid Van Loock, Frederik [0000-0003-0581-2238] dc.publisher.college Peterhouse dc.type.qualificationtitle PhD in Engineering cam.supervisor Fleck, Norman cam.supervisor.orcid Fleck, Norman [0000-0003-0224-1804] cam.thesis.funding true
﻿

### This item appears in the following Collection(s)

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