Current research interest in multi-scale modeling of cement paste requires accurate characterization of the time-dependent mechanical properties of the material, particularly the C-S-H phase. Nanoindentation is evaluated as a tool for measuring both the instantaneous and the short-term viscoelastic properties of cement paste. Atomic force microscopy (AFM) based indentation is compared to conventional nanoindentaion in measuring mechanical properties of cement pastes. Time-dependent solutions are derived to characterize creep indentation tests performed on hardened cement paste and to extract the time-dependent properties. The effect of approximating C-S-H viscoelastic properties with a time-independent Poisson's ratio is discussed, and arguments for utilizing a time-independent Poisson's ratio for short-term response are presented. In evaluating AFM as a mechanical characterization tool, various analytical and numerical modeling approaches are compared. The disparities between the numerical self-consistent approach and analytical solutions are determined and reported. The measured elastic Young's modulus values acquired by AFM indentation tests are compared to Young's modulus values from nanoindentation measurements from cement paste. These results show that the calcium silicate hydrate (C-S-H) phase of hydrated portland cement has different properties on the nanometric scale than on the micron scale. Packing density of C-S-H particles is proposed as an explanation for the disparity in the measured results. The AFM measured uniaxial viscoelastic compliance values are compared to similar values obtained with traditional nanoindentation for the same material. The comparison of these results shows that the calcium silicate hydrate (C-S-H) phase of portland cement has similar but distinct properties on the sub micron scale than on the micron scale. Additionally, the effect of moisture is evaluated by controlling the relative humidity (RH) of the testing environment between 40% and 100% plus, or wet. The viscoelastic compliance appears to be highest at 40% RH and the material appears to be less compliant at higher relative humidity levels. Possible mechanisms controlling the viscoelastic deformation are presented and evaluated in conjunction with the moisture related poromechanical effect.

An anti-reflective (AR) lens is an ultrathin multilayered structure composing of AR coatings on a lens substrate. These coatings can be made by a spin-coating process with a nanocomposite of UV curable acrylic monomers and well dispersed metal oxide nanoparticles. The in-situ UV polymerization rate was reduced by oxygen inhibition and the absorption of UV energy by the metal oxide nanoparticles. There are few studies of the mechanical properties of ultrathin polymeric coatings that include the effects of substrates, the viscoelastic behaviors of polymers in submicron scales and the effects of multilayered coatings. With a coating system based on UV cured dipentaerythritol pentaacrylate on silicon wafer substrates, nanoindentation tests showed that the nominal reduced contact modulus increased with the indentation load and penetration depth due to the effect of the substrate, in quantitative agreement with an elastic contact model. Ultrathin polymeric coatings subjected to constant indentation loads exhibit shear-thinning during flow. None of the models examined completely described the elastic response of an ultrathin polymeric coating on a compliant plastic substrate. The effective modulus was a function of coating-substrate property, indenter tip size, coating thickness, adhesion and residual stress. It was logarithmic dependent on the ratio of the indentation depth to the coating thickness prior to coating fracture. An elastic model, assuming shear-lag and a plane-stress state, was used to estimate the interfacial strength between a submicron coating and a compliant substrate. The critical indentation load for the indentation-induced delamination of the coating from the substrate increased with the third power of the indentation depth and was a linear function of the reciprocal of the coating thickness. The interfacial strength was 70.4 MPa. Mechanical properties and fracture characteristics of CVD ceramic and nanocomposite coatings on polymer substrates were evaluated by nanoindentation and nanoscratching tests. The AR lenses made with polymer nanocomposite coatings have better mechanical properties due to the close match of properties between the coatings and the plastic substrate. The new approach to making AR lenses with polymer nanocomposites on plastic substrate is promising.

Metallic glasses (MGs) usually have high strength, high hardness and high elastic strain limit. However, the deformation mode and mechanism in metallic glasses are radically different from those in conventional crystalline materials with a long-range ordered structure. For crystalline materials, the intrinsic relationship between their mechanical properties and crystal structures has been well described by dislocation theory. In contrast, for amorphous materials, theories on the structures and controlling factors of localized shear-band formation are far from being complete. In this thesis, shear-banding behavior of MGs under nanoindentation was first reviewed. The hardness of MGs was found to be independent on the shape of indenter tip. The hardness drop during each pop-in was a constant for a given indenter tip. A nanoindentation-based method for measuring the shear resistance of MGs was further developed. The hardness of MGs was largely affected by residual stresses, especially the tensile residual stress. Significant softening could be caused by tensile residual stress and the softening was attributed to the creation of extra free volume. The hardness of MGs was demonstrated to be extremely sensitive to the initial free volume in the material. Spherical indentation was also conducted on stressed MG sample to study the effect of residual stress on the first shear-band formation. It was found the critical shear stress for the shear-band formation was essentially a constant. The constant critical shear stress was correlated with a critical free volume in the material. Spherical indentation was further carried out at elevated temperature but well below glass transition temperature to explore the temperature effect on shear-band nucleation. Localized shear-banding was observed to be the dominant deformation mode at all temperatures. The shear stress at first pop-in or the onset of yielding decreased with temperature, and the activation energy and the size of shear transformation zone (STZ) were measured. Shear-band nucleus was estimated to be 10~20 nm and independent on temperature. Micro-compression tests were further performed on micro-sized pillar samples at different temperatures. The strength-temperature relationship could be explained by the constant viscosity concept, suggesting shear-banding was a stress-induced glass transformation.

Doctor of Philosophy(PhD) / Objectives As the outer cover of teeth structure, enamel is the hardest, stiffest and one of the most durable load-bearing tissues of the human body. Also, enamel is an elegantly designed natural biocomposite. From a material science point of view, scientists are interested in the structure and function of the nature material. How does nature design the material to meet its functional needs? From a dental clinic point of view, dental practitioners are keen to know the properties of enamel and compare it with different dental materials. What kind of dental materials can best simulate enamel as a restoration in the oral cavity? The research presented in this thesis on the mechanical behaviour of enamel in respect of its structural and compositional characteristics will attempt to provide answers or indications to the above questions. Theoretical analysis, as well as experimental investigations of both man-made and natural composites materials, has shown that hierarchical microstructure and organic matrix glues the inorganic particles together and plays an important role in regulating the mechanical properties of the composite. Bearing this finding in mind, in the current investigations, we assume the hierarchical microstructure and trace protein remnants in enamel regulate the mechanical behaviour of the natural biocomposite to meet its functional needs as a load bearing tissue with superb anti-fatigue and wear resistant properties. One of the important reasons that dental hard tissues haven’t been thoroughly investigated is due to the limited sample volume. Fortunately, with the development of nanoindentation technique and equipment, it is now possible to explore the mechanical properties of small volume samples. The application of nanoindentation on dental hard tissues has been documented. However, most investigations have concentrated on only reporting the basic mechanical properties such as elastic modulus and hardness. Very few of them have taken the role of microstructure and composition of these natural biocomposites into their considerations. The main aim of this investigation is to interpret how microstructural and compositional features of enamel regulate its mechanical behaviour. To achieve this goal, the analytical methods considering nanoindentation data need to be expanded so that more information not only elastic modulus and hardness but also stress-strain relationship, energy absorption ability, and creep behaviour may be evaluated with this technique. These new methods will also be of benefit to dental material evaluation and selection. Materials and methods Based on the Oliver-Pharr method1 for the analysis of nanoindentation data, Hertzian contact theory2 and Tabor’s theory3, a spherical nanoindentation method for measuring the stress-strain relationship was developed. Furthermore, nanoindentation energy absorption analysis method and nanoindentation creep test were developed to measure the inelastic property of enamel. With the above methods, sound enamel samples were investigated and compared with various dental materials, including dental ceramics and dental alloys. • Firstly, using a Berkovich indenter and three spherical indenters with 5, 10 and 20 µm nominal radius, the elastic modulus, hardness and stress-strain relationship of different samples were investigated and compared. • Secondly, mechanical properties of enamel in respect to its microstructure were investigated intensively using different indenters by sectioning teeth at different angles. • Thirdly, inelastic behaviour of enamel such as energy absorption and creep deformation were observed and compared with a fully sintered dense hydroxyapatite (HAP) disk to illustrate the roles of protein remnants in regulating the mechanical behaviour of enamel. • Fourthly, to confirm the functions of protein remnants in controlling mechanical behaviour of enamel, enamel samples were treated under different environments such as burning (300°C exposure for 5 min), alcohol dehydration and rehydration to change the properties of proteins before the nanoindentation tests. • Lastly, micro-Raman spectroscopy was employed to measure and compare the indentation residual stresses in enamel and HAP disk to evaluate the role of both hierarchical microstructure and protein remnants in redistributing the stresses and reinforcing the mechanical response of enamel to deformation. Results and significance Nanoindentation is an attractive method for measuring the mechanical behaviour of small specimen volumes. Using this technique, the mechanical properties of enamel were investigated at different orientations and compared with dental restorative materials. From the present study, the following results were found and conclusions were drawn.  Although some newly developed dental ceramics have similar elastic modulus to enamel, the hardness of these ceramic products is still much higher than enamel; in contrast, despite the higher elastic modulus, dental metallic alloys have very similar hardness as enamel. Furthermore, enamel has similar stress-strain relationships and creep behaviour to that of dental metallic alloys. SEM also showed enamel has an inelastic deformation pattern around indentation impressions. All of these responses indicated that enamel behaves more like a metallic material rather than a ceramic.  Elastic modulus of enamel is influenced by highly oriented rod units and HAP crystallites. As a result, it was found to be a function of contact area. This provides a basis to understand the different results reported in the literature from macro-scale and micro-scale tests. Anisotropic properties of enamel, which arise from the rod units, are well reflected in the stress-strain curves. The top surface (perpendicular to the rod axis) is stiffer and has higher stress-strain response than an adjacent cross section surface because of the greater influence of the prism sheaths in the latter behaviour.  Enamel showed much higher energy absorption capacity and considerably more creep deformation behaviour than HAP, a ceramic material with similar mineral composition. This is argued to be due to the existence of minor protein remnants in enamel. Possible mechanisms include fluid flow within the sheath structure, protein “sacrificial bond” theory, and nano-scale friction within sheaths associated with the degustation of enamel rods.  A simple model with respect of hierarchical microstructure of enamel was developed to illustrate the structural related contact deformation mechanisms of human enamel. Within the contact indentation area, thin protein layers between HAP crystallites bear most of the deformation in the form of shear strain, which is approximately 16 times bigger than contact strain in the case of a Vickers indenter. By replotting energy absorption against mean strain value of a protein layer, data from different indenters on enamel superimposed, validating the model. This model partially explained the non-linear indentation stress-strain relationship, inelastic contact response and large energy absorption ability of enamel and indicated the inelastic characteristics of enamel were related to the thin protein layers between crystallites.  Following different treatments, mechanical properties of enamel changed significantly. By denaturing or destroying the protein remnants, mechanical behaviour, especially inelastic abilities of enamel decreased dramatically, which indicates matrix proteins endow enamel better performance as a load bearing calcified tissue.  Comparison of Raman derived residual maps about indentations in enamel and a sintered homogeneous HAP showed the hierarchical structure influenced the residual stress distribution within enamel. Moreover, less residual stresses were found in enamel and were a consequence of the protein remnants. These are evidence as to how the microstructure meets the functional needs of the enamel tissue. In general, evidence from different approaches indicated that the hierarchical microstructure and small protein remnants regulated the mechanical behaviour of enamel significantly at various hierarchical levels utilising different mechanisms. This investigation has provided some basis for understanding natural biocomposites and assisting with dental clinic materials selection and treatment evaluation procedures. References 1. Oliver WC, Pharr GM. An improved technique for determining hardness and elastic modulus using load and displacement sensing indentation experiments. J Mater Res. 1992;7(6):1564-83. 2. Hertz H. Miscellaneous Papers. London: Jones and Schott, Macmillan; 1863. 3. Tabor D. Hardness of Metals. Oxford: Clarendon Press; 1951.

Orientador: Sérgio Eduardo de Paiva Gonçalves / Banca: Alessandra Bühler Borges / Banca: Andrea Anido Anido / Resumo: O objetivo desta pesquisa foi avaliar a influência do laser Nd:YAG nas propriedades mecânicas (dureza e módulo de elasticidade) da interface adesiva, utilizando a técnica da nanoindentação, empregando-se sistema adesivo convencional Adper Single Bond 2 - 3M ESPE (SB) ou autocondicionante Clearfil SE Bond - Kuraray (CSE). Doze terceiros molares humanos tiveram suas superfícies oclusais desgastadas até a exposição da dentina superficial. Uma cavidade circular padronizada com fresa 3053 foi realizada na superfície oclusal proporcionando 2 mm de dentina remanescente. Os espécimes foram embutidos em resina acrílica, e seccionados no sentido mésio-distal, sendo as 24 hemi-coroas obtidas divididas em quatro grupos: Grupo controle (SBC) - aplicação do sistema SB de acordo com as recomendações do fabricante; Grupo laser (SBL) - aplicação do sistema adesivo SB e tratamento com laser Nd:YAG (140mJ/cm2/60s/não contato); Grupo controle (CSEC) - aplicação do sistema adesivo autocondicionante CSE de acordo com as recomendações do fabricante; Grupo laser (CSEL)- aplicação do sistema adesivo autocondicionante CSE e tratamento com laser Nd:YAG (140mJ/cm2/60s/não contato). Após a polimerização dos sistemas adesivos, foram aplicados dois incrementos da resina composta Filtek Z 350 (3M ESPE). Os corpos-de-prova foram imersos em água destilada e armazenados por 24h em estufa 37ºC e submetidos à nanoidentação em aparelho Nano Indenter® XP (MTS®, MN, EUA).. Os resultados foram submetidos aos testes estatísticos de Análise de Variância (ANOVA), Tukey e t-Student (p<0,05). Concluiu-se que a aplicação do laser Nd:YAG em ambos os sistemas adesivos não alterou o nível de dureza da interface adesiva, no entanto alterou o módulo de elasticidade / Abstract: The aim of this study was to evaluate the influence of Nd: YAG laser on the mechanical properties (hardness and modulus of elasticity) of the adhesive interface, using the technique of nanoindentation, employing conventional adhesive system Single Bond 2 3M ESPE (SB) or selfetching adhesive system Clearfil SE Bond - Kuraray (CSE). On 12 human molars, a flat superficial dentin surface was exposed by abrasion. A standardized circular cavity with bur 3053 was performed on the occlusal surface and dentin thickness was standardized in 2 mm. The specimens were embedded in resin acrylic and sectioned mesio-distally through their long axes, and the 24 hemi-crowns obtained divided into four groups: Control Group (SBC) - the application of SB system according to the manufacturer's recommendations; Laser Group (SBL) - SB adhesive system and treatment with Nd: YAG laser (140mJ/cm2/60s/no contact) Control Group (CSEC) - application of CSE self-etching adhesive system according to the manufacturer's recommendations; Laser Group (CSEL) - application of CSE self-etching adhesive system and treatment with Nd: YAG laser (140mJ/cm2/60s/no contact). After polymerization of the adhesives, were applied two increments of composite resin Filtek Supreme and specimens were immersed in distilled water and stored for 24 hours at 37 ºC and submitted to nanoidentation in Nano Indenter ® XP (MTS ®, MN, USA. Nanoindentation were made on composite resin, adhesive system, hybrid layer and dentin. The results were analyzed by a tree-way ANOVA, Tukey and e t-Students (p<0,05). It was concluded that the application of Nd:YAG laser in both adhesive systems did not change hardness level of hybrid layer, however chanded the elastic modulus / Mestre

The launch of silicone hydrogel contact lenses has led to a rise in the incidence of mechanically-related clinical complications, which is thought to be due to the increased stiffness of these materials compared to conventional hydrogel lens materials. The mechanical characteristics of hydrogel contact lenses have traditionally been investigated using tensile testing which investigated the bulk material characteristics. This thesis presents a study intended to establish a repeatable method for local mechanical measurement of hydrogel contact lenses using nanoindentation. Hydrogel materials in phosphate buffered saline were indented using a Hysitron Triboindenter mounted on a Veeco Explorer AFM using Triboscope software (version 3.5a) with a specially constructed wet cell. A model hydrogel (poly(HEMA-MMA)) was used to validate the methodology and investigate a the effect of controlled change in specimen thickness. A range of commercially available hydrogel contact lenses were then characterised (including conventional and silicone hydrogel lenses) using the same method. Two different analytical techniques were employed to determine the mechanical properties data; elastic analysis and a time-dependent viscoelastic analytical technique.A strong influence of specimen thickness on apparent mechanical properties was seen with the elastic analysis and an empirical relationship was derived to correct for this which was found to be appropriate for all contact lens specimens studied and reported in the thesis. The viscoelastic analysis results were more complex and exhibited a less clear influence of specimen thickness. However, as this is a very simple approximation as contact lenses are suspected to be poroelastic rather than viscoelastic this work could not be fully resolved in the scope of this thesis. For all contact lenses analysed, nanoindentation produced data similar to that found with conventional tensile testing, however, there was evidence for a slight dependence of elastic properties across the lens that does not correlate with sample thickness. This thesis shows the development of a way of accounting for the variation of thickness of a range of contact lenses, and demonstrated that traditional analysis is accurate enough to determine local differences in modulus across contact lenses. The viscoelastic analysis may be more appropriate for hydrogels, however, it produced irregularities that will require further work to fully resolve.

Nanoindentation has brought in many features of research over the past decade. This novel technique is capable of producing insights into the small ranges of deformation. This special point has brought a lot of focus in understanding the deformation behavior under the indenter. Nickel, iron, tungsten and copper-niobium alloy system were considered for a surface deformation study. All the samples exhibited a spectrum of residual deformation. The change in behavior with indentation and the materials responses to deformation at low and high loads is addressed in this study. A study on indenter geometry, which has a huge influence on the contact area and subsequently the hardness and modulus value, has been attempted. Deformation mechanisms that govern the plastic flow in materials at low loads of indentation and their sensitivity to the rate of strain imparted has been studied. A transition to elastic, plastic kind of a tendency to an elasto-plastic tendency was seen with an increase in the strain rate. All samples exhibited the same kind of behavior and a special focus is drawn in comparing the FCC nickel with BCC tungsten and iron where the persistence of the elastic, plastic response was addressed. However there is no absolute reason for the inconsistencies in the mechanical properties observed in preliminary testing, more insights can be provided with advanced microscopy techniques where the study can be focused more to understand the deformation behavior under the indenter. These experiments demonstrate that there is a wealth of information in the initial stages of indentation and has led to much more insights into the incipient stages of plasticity.

Mechanics of bone is widely studied and researched, mainly for the study of fracture. This has been done mostly on a macro scale. In this work hierarchical nature of bone has been explored to investigate bone mechanics in more detail. Flexural test were done to classify the bones according to their strength and deflection. Raman spectroscopy analysis was done to map the mineralization, collagen crosslinking changes across the thickness of the bone. Nanoindentation was done to map indentation hardness and indentation modulus across femoral cortex of the bone. The results indicate that the composition of the bone changes across the thickness of the femoral cortex. The hypothesis is confirmed as increase in mineralization, carbonate to phosphate ratio and collagen crosslinking shows the effect as increased indentation hardness and modulus and decreased deflection.

Two families of PVD hard coatings were successfully used for high performance end milling of hardened H13 tool steel. The first family of coatings are AlCrN-based, they are used for wet machining and the other family is based on TiAlCrSiYN coating and are used for dry machining of H13. It was shown that there is a strong potential for further advancement in the wear performance of the coatings by improving the coating architecture as well as by varying the deposition parameters used during their synthesis. A number of deposition parameters of the coatings show a strong impact on wear performance of the cutting tools. Wear performance was related to the structure and a number of nano-mechanical characteristics of the coating layer assessed using the NanoTest system produced by Micro Materials. It was shown that critical characteristics like nano-hardness, loading support factor and nano-scaled scratch resistance can be used to predict the wear performance of a cutting tool. / Thesis / Master of Applied Science (MASc)

BACKGROUND: The cornea is the outer portion of the eye and protects the eye from infection or debris. When the cornea becomes compromised due to age and disease (specifically Diabetes Mellitus), it becomes impaired and can have profound impacts on an individual’s quality of life by leading to vision loss or blindness. The different layers of the cornea all contain many proteins and collagen, and have varying degrees of thickness and biomechanical properties. Stiffness in the cornea has either been measured via the use of AFM (Atomic Force Microscopy) which involves removing a slice of the cornea and adhering to the surface, as a function of IOP (Intraocular Pressure), or tensile testing. Previous research has also used the nanoindenter to measure the stiffness of different layers in the intact globe (eyeball) within the mouse head or by adhering to PEG submerged in PBS. However, no studies to our knowledge have used the intact globe exposed to air and placed on a 3D printed model to measure different corneal layers via the use of nanoindentation. METHODS: 6 C57BL/6J mice were obtained between 8-12 and 27 weeks of age, had the eyes extracted, and half remained with intact epithelium while the other half had the epithelium abraded with a 1.5 mm trephine. The eyes were placed in keratinocyte solution (KCM) for preservation while they were transported to the site with a nanoindenter. The globes were then placed on a 3D printed holder, cornea facing up, and irrigated with KCM solution in between indentation measurements. The PIUMA Optics 11 Nanoindenter was used to measure the Effective Young’s Modulus of the epithelium, basement membrane, and stroma. The Oliver & Pharr modeling was used as opposed to the Hertzian Model due to the biomechanical and adhesion properties of the eye. RESULTS: A comparison of control mice at 9 weeks shows an average Effective Young’s Modulus of 30.73 kPa, and an average Effective Young’s Modulus for 15 week old mice of 62.50 kPa for the epithelium. The average Effective Young’s Modulus of the basement membrane for 9 week control mice was ~6.2 kPa and for older 27 week mice was ~6 kPa. The Effective Young’s modulus for the stroma of 9 week old mice was ~68.3 kPa and for 27 week old mice was ~ 222.7 kPa. CONCLUSION: It was observed that stiffer substrates (in this instance, stiffer layers) require stiffer probes. The opposite is true of softer substrates, which require softer probes. It is beneficial in either instance to use a larger tip radius as there will be more contact and surface area measurement, so the probe has less recoil due to the adhesion from the corneal layers. The values observed in this study correlated with the values seen in the study conducted by Xu et al. However, the basement membrane values were different and could be due to probe specifications or layer thinness. Additional studies are needed to observe changes in Young’s Modulus based on probe characteristics with diseases such as Diabetes Mellitus (DM).