| Summary: | This study mainly investigated how the mechanical behaviour of alumina trihydrate (ATH) filled Poly (methyl methacrylate) (PMMA) composites is affected by changes in certain parameters such as the volume fraction of and the size of the ATH particles. Although numerous studies have been conducted in this area, the effect of the microstructure is very difficult to explain because of the many factors which are involved and affect the mechanical behaviour of particle-filled composites. In this study, a systematic study, where volume fraction and particle diameter are varied, is presented. Modelling technique, both micromechanical analytical and finite element models, are used to achieve understanding of the experimentally observed mechanical behaviour of the composites. Five groups of composites were tested: Composite A: 15 μm, 34.7 vol. %, B: 8 μm, 39.4 vol. %, C: 15 μm, 39.4 vol. %, D: 25 μm, 39.4 vol. % and E: 15 μm, 44.4 vol. %. Flexural tests, uniaxial tensile tests, single edge notch bending (SENB) tests were performed at different temperatures. The elastic modulus of the composites increased as the filler content increased, whilst the change in particle diameter hardly affected the elastic modulus. Due to the competition between the reinforcing effect of the rigid particles and the weakening effect of the particle agglomeration on the composites, the increase in filler content showed little effect on the strength of the composites. On the other hand, as the particle diameter increased, the strength of the composite decreased. The fracture toughness, G_IC, of the composites is negatively correlated with the filler content, whilst increased with the increasing particle diameter. The FE simulation has great advantages comparing to micromechanical analytical models. For predicting the elastic modulus of the particle filled composites, the FE simulation can make as good prediction as the Lielens model, the prediction of which agreed well with the experimental data. The FE simulation can also predict the strength of particle-filled composites if an appropriate crack initiation stress of the matrix is used. The stress field obtained using the FE simulation led to a better understanding of how the microstructures of the composites affect their mechanical behaviour. In addition, the application of the SEM image-converted RVEs, i.e. real microstructure approach, takes into consideration the effect of particle agglomeration, which is another big improvement comparing to micromechanical analytical models.
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