The management of significant bone defects, delayed and non-union of fractures can be extremely challenging. Development of specific treatment is hindered by an absence of information regarding the molecular events which regulate these processes. In this thesis, a bilateral cancellous bone defect model of the femur and tibia was developed in a rodent and the spatiotemporal profile of TGF-β, BMP 2 and 7, Smads 1, 4 and 5 characterised. Next, the capability of acid solution to augment healing was tested in both a bone defect and in a closed femoral fracture model. Finally, a long term oestrogen deficiency (OVX) rat model of postmenopausal osteoporosis was characterised and the spatiotemporal profiles of IGF-1, IGFR-1, MMP-1, MMP-3, MMP-9, MMP-13, TIMP-1, TIMP-2, BMP-2, BMP-4, BMP-7, TGF-β, Smad4, Smad7, VEGF, Flt-1, Ihh and FGF-2 were compared in femoral osteotomies between OVX and Sham groups. The bilateral cancellous defect model was successfully created with a number of advantages with which to recommend its use in future studies. TGF-β, BMP 2 and 7, Smads 1, 4 and 5 had characteristic spatiotemporal profiles during cancellous bone defect healing suggesting that they have a regulatory role. The results of the acid study were inconclusive and problems with substance delivery and maintenance at the desired site need to be addressed in the future to fully test this hypothesis. No significant differences were detected on histology or three-point mechanical testing between the fracture calluses of acid and control groups. In the final study, OVX rats after six months had significantly increased weight and decreased bone mineral density compared to their sham counterparts. A histological delay in osteotomy healing was observed in the OVX group but no significant differences on tensile testing were seen between OVX and Sham groups up to six weeks. Immunohistochemistry revealed that delayed healing may be due to the down-regulation of IGF-1, BMP-2, 4, and 7 and the up-regulation of MMP-3 in OVX compared to Sham groups. In conclusion, the results of this thesis give some insight into the molecular biology of bone defects and osteoporotic fractures. This information may also be useful in the development of specific treatments aimed at augmenting healing in bone defects and osteoporotic fractures.

The introduction of carbon-fibre reinforced plastics in loadbearing automotive structures provides a great potential toreduce vehicle weight and fuel consumption. To enable themanufacture and assembly of composite structural parts,reliable and cost-effective joining technologies must bedeveloped. This thesis addresses several aspects of joining andload introduction in carbon-fibre reinforced plastics based onnon-crimp fabric reinforcement. The bearing strength of carbon fibre/epoxy laminates wasinvestigated considering the effects of bolt-hole clearance.The laminate failure modes and ultimate bearing strength werefound to be significantly dependent upon the laminate stackingsequence, geometry and lateral clamping load. Significantreduction in bearing strength at 4% hole deformation was foundfor both pin-loaded and clamped laminates. The ultimatestrength of the joints was found to be independent of theinitial bolt-hole clearance. The behaviour of hybrid (bolted/bonded) joints wasinvestigated both numerically and experimentally. Athree-dimensional non-linear finite element model was developedto predict the load transfer distribution in the joints. Theeffect of the joint geometry and adhesive material propertieson the load transfer was determined through a parameter study.An experimental investigation was undertaken to determine thestrength, failure mechanisms and fatigue life of hybrid joints.The joints were shown to have greater strength, stiffness andfatigue life in comparison to adhesive bonded joints. However,the benefits were only observed in joint designs which allowedfor load sharing between the adhesive and the bolt. The effect of the environment on the durability of bondedand hybrid joints was investigated. The strength and fatiguelife of the joints was found to decrease significantly withincreased ageing time. Hybrid joints demonstrated increasedfatigue life in comparison to adhesive bonded joints afterageing in a cyclic freeze/thaw environment. The strength and failure mechanisms of composite laminatessubject to localised transverse loading were investigatedconsidering the effect of the specimen size, stacking sequenceand material system. Damage was found to initiate in thelaminates at low load levels, typically 20-30% of the ultimatefailure load. The dominant initial failure mode wasintralaminar shear failure, which occurred in sub-surfaceplies. Two different macromechanical failure modes wereidentified, fastener pull-through failure and global collapseof the laminate. The damage patterns and ultimate failure modewere found to depend upon the laminate stacking sequence andresin system. Finite element analysis was used to analyse thestress distribution within the laminates and predict first-plyfailure. Keywords:Composite, laminate, bearing strength,joining, load introduction, hybrid joint, finite elementanalysis, mechanical testing.

The mechanical response of geomaterials is highly influenced by geometrical and material heterogeneity. To date, most modelling practices consider heterogeneity qualitatively and the choice of input parameters can be subjective. In this study, a novel approach to combine detailed micro-scale characterization with modelling of heterogeneous geomaterials is presented. The influence of micro-scale heterogeneity and microcracks on the mechanical response and brittle fracture of a crystalline rock was studied using numerical and experimental tools. An existing Combined Finite-Discrete element (FEM/DEM) code was extended to suit heterogeneous, discontinuous, brittle rocks. By conducting grid micro-indentation and micro-scratch tests, the Young's modulus and fracture toughness of the constituent phases of the rock were obtained and used as accurate input parameters for the numerical models. The models incorporated the exact phase mapping obtained from a MicroCT-scanned specimen and the existing microcrack density obtained from thin section analysis. The results illustrated that by incorporating accurate micromechanical input parameters and the intrinsic rock geometric features, the numerical simulations could more accurately predict the mechanical response of the specimen, including the fracture patterns and tensile strength. The numerical simulations illustrated that microstructural flaws such as microcracks should be included in the models to more accurately reproduce the rock strength. In addition, the differential elastic deformations caused by rock heterogeneity altered the stress distribution in the specimen, creating zones of local tensile stresses, in particular, on the boundaries between different mineral phases. As a result, heterogeneous models exhibited rougher fracture surfaces. MicroCT observations emphasized the influence of heterogeneity and, in particular, biotite grains on the fracture trajectories in the specimens. Favourably oriented biotite flakes and cleavage splitting significantly deviated the cracks. The interaction of the main crack with perpendicular cleavage planes of biotite caused strong crack deviation and termination. Considering heterogeneity and the strength degradation caused by microcracks, the simulations captured reasonably accurate mechanical responses and failure mechanisms for the rock, namely, the nonlinear stress-strain relationships. The insights presented in this study improve the understanding of the role of heterogeneity and microstructure on damage and mechanical behaviour of brittle rock.

The mechanical response of geomaterials is highly influenced by geometrical and material heterogeneity. To date, most modelling practices consider heterogeneity qualitatively and the choice of input parameters can be subjective. In this study, a novel approach to combine detailed micro-scale characterization with modelling of heterogeneous geomaterials is presented. The influence of micro-scale heterogeneity and microcracks on the mechanical response and brittle fracture of a crystalline rock was studied using numerical and experimental tools. An existing Combined Finite-Discrete element (FEM/DEM) code was extended to suit heterogeneous, discontinuous, brittle rocks. By conducting grid micro-indentation and micro-scratch tests, the Young's modulus and fracture toughness of the constituent phases of the rock were obtained and used as accurate input parameters for the numerical models. The models incorporated the exact phase mapping obtained from a MicroCT-scanned specimen and the existing microcrack density obtained from thin section analysis. The results illustrated that by incorporating accurate micromechanical input parameters and the intrinsic rock geometric features, the numerical simulations could more accurately predict the mechanical response of the specimen, including the fracture patterns and tensile strength. The numerical simulations illustrated that microstructural flaws such as microcracks should be included in the models to more accurately reproduce the rock strength. In addition, the differential elastic deformations caused by rock heterogeneity altered the stress distribution in the specimen, creating zones of local tensile stresses, in particular, on the boundaries between different mineral phases. As a result, heterogeneous models exhibited rougher fracture surfaces. MicroCT observations emphasized the influence of heterogeneity and, in particular, biotite grains on the fracture trajectories in the specimens. Favourably oriented biotite flakes and cleavage splitting significantly deviated the cracks. The interaction of the main crack with perpendicular cleavage planes of biotite caused strong crack deviation and termination. Considering heterogeneity and the strength degradation caused by microcracks, the simulations captured reasonably accurate mechanical responses and failure mechanisms for the rock, namely, the nonlinear stress-strain relationships. The insights presented in this study improve the understanding of the role of heterogeneity and microstructure on damage and mechanical behaviour of brittle rock.

<p>The introduction of carbon-fibre reinforced plastics in loadbearing automotive structures provides a great potential toreduce vehicle weight and fuel consumption. To enable themanufacture and assembly of composite structural parts,reliable and cost-effective joining technologies must bedeveloped. This thesis addresses several aspects of joining andload introduction in carbon-fibre reinforced plastics based onnon-crimp fabric reinforcement.</p><p>The bearing strength of carbon fibre/epoxy laminates wasinvestigated considering the effects of bolt-hole clearance.The laminate failure modes and ultimate bearing strength werefound to be significantly dependent upon the laminate stackingsequence, geometry and lateral clamping load. Significantreduction in bearing strength at 4% hole deformation was foundfor both pin-loaded and clamped laminates. The ultimatestrength of the joints was found to be independent of theinitial bolt-hole clearance.</p><p>The behaviour of hybrid (bolted/bonded) joints wasinvestigated both numerically and experimentally. Athree-dimensional non-linear finite element model was developedto predict the load transfer distribution in the joints. Theeffect of the joint geometry and adhesive material propertieson the load transfer was determined through a parameter study.An experimental investigation was undertaken to determine thestrength, failure mechanisms and fatigue life of hybrid joints.The joints were shown to have greater strength, stiffness andfatigue life in comparison to adhesive bonded joints. However,the benefits were only observed in joint designs which allowedfor load sharing between the adhesive and the bolt.</p><p>The effect of the environment on the durability of bondedand hybrid joints was investigated. The strength and fatiguelife of the joints was found to decrease significantly withincreased ageing time. Hybrid joints demonstrated increasedfatigue life in comparison to adhesive bonded joints afterageing in a cyclic freeze/thaw environment.</p><p>The strength and failure mechanisms of composite laminatessubject to localised transverse loading were investigatedconsidering the effect of the specimen size, stacking sequenceand material system. Damage was found to initiate in thelaminates at low load levels, typically 20-30% of the ultimatefailure load. The dominant initial failure mode wasintralaminar shear failure, which occurred in sub-surfaceplies. Two different macromechanical failure modes wereidentified, fastener pull-through failure and global collapseof the laminate. The damage patterns and ultimate failure modewere found to depend upon the laminate stacking sequence andresin system. Finite element analysis was used to analyse thestress distribution within the laminates and predict first-plyfailure.</p><p><b>Keywords:</b>Composite, laminate, bearing strength,joining, load introduction, hybrid joint, finite elementanalysis, mechanical testing.</p>

Dynamic abnormal grain growth (DAGG) is a phenomenon by which single crystals up to centimeters in length are produced at elevated temperature during the application of strain. DAGG was previously demonstrated in commercial-purity molybdenum (Mo) materials. This is the first investigation to confirm DAGG in another material, tantalum (Ta). Previous experiments initiated and propagated DAGG using constant true-strain rate tensile tests, but this study demonstrates that DAGG can also occur under constant true-stress tensile conditions. A Mo material was tested under constant true stress, and two Ta materials were tested under constant true-strain rate. The effects of temperature, stress, strain rate, initial microstructure and texture on tensile test data and the resulting microstructures are examined. The microstructures of the Ta materials are analyzed using electron backscatter diffraction (EBSD) data to quantify the orientation, deformation, grain boundary character, and slip properties of the DAGG grains and unconsumed microstructure. The DAGG grains were found to be relatively undeformed compared to the unconsumed microstructure following DAGG and to not be oriented favorably, or unfavorably, for slip. The grain boundaries between DAGG grains in one Ta material were found to commonly have [sigma]3 character. This was likely due to a strong initial <111>-fiber texture. Previous investigations of DAGG in Mo indicated that DAGG grains commonly grow along the surface of the specimen, but this was not observed with significant frequency in Ta. Results suggest that the distance the DAGG grain boundary travels is proportional to the accumulated strain during DAGG, and the velocity of the DAGG grain boundary is proportional to the applied strain rate but is not related to the orientation of the DAGG grain or its slip properties. / text

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Among the potential high temperature shape memory alloys, due to its low cost, medium ductility and high work output NiTiHf seems to be the most promising HTSMA for a wide range of applications in the 100-250ºC. A detailed investigation into the shape memory properties and transformation behavior for the Ni-rich HTSMA with the compositions of Ni45.3Cu5Ti29.7Hf20, Ni50.3Ti29.7Hf20 and Ni45.3Pd5Ti29.7Hf20 was carried out. It is possible to form Ni-rich precipitates in Ni-rich NiTiHf alloys and tailor the TTs by heat treatments that results in increased strength and stable response at high temperatures. The coherent Ni-rich precipitates deplete the Ni content from the matrix increasing the transformation temperatures and strengthen the material by hindering the dislocation motion. The effect of aging on the microstructure, shape memory and mechanical properties are revealed. Optimum aging conditions have been found determined to get the most favorable combination of high transformation temperatures with stable and good shape memory properties. The Ni50.3Ti29.7Hf20 and Ni45.3Pd5Ti29.7Hf20 aged at 500ºC-600 ºC were found to be formidable candidates for high temperature applications.

<p>Extending the functional lifetime of acrylic poly(methyl methacrylate) (PMMA) bone cement may reduce the number of revision total joint replacement (TJR) surgeries performed each year. We developed a system utilizing an encapsulated water-reactive, FDA-approved tissue adhesive, 2-octyl cyanoacrylate (OCA), as a healing agent to repair microcracks within a bone cement matrix. The proposed research tested the following hypotheses: (1) reactive OCA can be successfully encapsulated and the resulting capsules thoroughly characterized; (2) the static mechanical properties of the PMMA composite can be improved or maintained through inclusion of an optimal wt% of OCA-containing capsules; (3) PMMA containing encapsulated OCA has a prolonged lifetime when compared with a capsule-free PMMA control as measured by the number of cycles to failure; and (4) the addition of capsules to the PMMA does not significantly alter the biocompatibility of the material. Based on the experiments reported herein, the primary conclusions of this dissertation are as follows: (1) functional OCA can be encapsulated within polyurethane spheres and successfully incorporated into PMMA bone cement; (2) lower wt% of capsules maintained the tensile, compressive, fracture toughness, and bending properties of the PMMA; (3) inclusion of 5 wt% of OCA-containing capsules in the matrix increased the number of cycles to failure when compared to unfilled specimens and those filled with OCA-free capsules; and (4) MG63 human osteosarcoma cell proliferation and viability were unchanged following exposure to OCA-containing PMMA when compared with a capsule-free control.</p> / Dissertation