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Title: Mechanics of calcite-polymer microcomposites using nanoindentation and micro-compression
Author: Ribeiro, Luis Manuel Pessanha
ISNI:       0000 0004 2740 7839
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2013
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The aim of this project is to investigate the suitability of specific polymers inclusions in improving some important mechanical properties of single crystals of calcite. The mechanical properties of synthetic and mineral single crystals of pure calcite are reported and compared with synthetic and biogenic crystals incorporating polystyrene particles or di-block co-polymer micelles and organic molecules respectively. The mechanical properties of these crystals are measured using nanoindentation and micro-compression techniques. It is shown that the crystals’mechanical properties obtained by the nanoindentation Oliver-Pharr method are influenced by the compliance of the resin substrate into which the crystal samples are embedded. The embedding of the crystals is shown to be necessary in order to achieve a flat surface onto which reliable indentation can be made. An estimate of the elastic moduli of the samples was obtained by using the Song-Pharr model, which takes into account substrate compliance. The hardness of all the tested samples was also recalculated by using conventional methods. By analyzing the obtained substrate independent data it was found that although the occlusion of co-polymer micelles reduced the modulus of pure calcite its hardness was not affected. This behaviour was not observed in the composites occluded with 200 nm polystyrene particles which showed a significant hardness reduction. The 20 nm co-polymer micelles also increased the specific hardness of the crystals whereas the 200 nm polystyrene particles showed no such behaviour. The micro-compression data showed that the 200 nm polystyrene particles could potentially be used to reduce the brittleness of calcite. Images of cracks, post-fracture of the crystals, indicated deformation of the polymer. This is evidence of the occurrence of a crack bridging mechanism. It was thought that this could lead to an enhancement of the strain at fracture and work of fracture of these composites when compared with pure calcite. Mechanical data from these tests showed however that the polystyrene particles’ occlusion was inadequate to increase the strain to fracture and the work of fracture of calcite. In addition to this the specific compressive strength, specific compressive modulus and specific compressive work of fracture of calcite also decreased with the addition of PS particles.
Supervisor: Eichhorn, Stephen Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available