The applications of elastic membrane range from determining the mechanical properties of biological cells by indentation tests to predicting the deformed shape of a large commercial tent structure. In this work, direct membrane theory and a particular Varga strain energy function are used to model the indentation and puncturing of an isotropic spherical elastic membrane containing a fluid with a rigid indenter. The balance laws are applied to obtain the governing differential equations and numerical shooting method is used to solve them. Furthermore, a global mode of failure is established by computing the energy stored at the punctured membrane and this value determines a critical value for the energy of the membrane beyond which the punctured state of the membrane is energetically preferred. An additional mode of failure is identified in which the membrane loses local convexity requirements and it corresponds to the local loss of elastic behavior of the membrane. / Graduate / 0548 / deris@Uvic.ca

OBJECTIVES: To test and compare the effects of static and cyclic loading on fracture toughness (K1C) and microhardness of dental restorative CAD/CAM materials. MATERIAL AND METHODS: Five commercially available CAD/CAM restorative materials were included in this study: Lava™ Ultimate Restorative (3M ESPE), IPS Empress® CAD (Ivoclar Vivadent), Enamic® (VITA), IPS e.max® CAD (Ivoclar Vivadent), and CERASMART™ (GC Dental). Polished rectangular bars 4×2×14 mm (n=30) were prepared from mill blocks for each material. Single notch of 0.5-1 mm in depth was made on the center of one length edge. Ten specimens per group for each material were randomly selected for 1) static mode, 2) after 100k cyclic loads, and 3) after 200k cyclic loads. The survival bars after the fatigue test were then subjected to a three-point flexural test. K1C values were determined on ‘single-edge-pre-crack-beams’ (SEPB) method. In addition, random specimens after the flexural test were selected for Vickers microhardness test from each group. Additionally indentation fracture method (IF) was used to determine surface fracture toughness for e.max CAD and Empress CAD. All the results were analyzed via ANOVA with Tukey’s HSD test or least square regression model using JMP Pro 12.0. RESULTS: The mean fracture toughness (K1C) of the material tested in static mode (3.2 MPa.m1/2 for e.max CAD, 2 MPa.m1/2 for Lava Ult, 1.95 MPa.m1/2 for Empress CAD, 1.92 MPa.m1/2 for Enamic, and 1.65 MPa.m1/2 for Cerasmart). The 100k fatigue group (4.02 MPa.m1/2 for e.max CAD, 3.06 MPa.m1/2 for Cerasmart, 2.55 MPa.m1/2 for Lava Ult, 2.01 MPa.m1/2 for Enamic, 1.94 MPa.m1/2 for Empress CAD) The 200k fatigue group (3.14 MPa.m1/2 for Cerasmart, 2.83 MPa.m1/2 for Lava Ult, 2.68 MPa.m1/2 for e.max CAD, 2.01 MPa.m1/2 for Enamic, 1.72 MPa.m1/2 for Empress CAD). While there was a significant difference in the mean fracture toughness (K1C) and (VHN) after fatigue of material tested (p<0.05). CONCLUSION: The CAD/CAM materials tested exhibited a higher K1C values after cyclic loading, along with lower K1C compared to the static group. In addition, K1C values by IF method exhibit lower K1C values after fatigue that was not a good way to test the fracture toughness value. / 2018-09-28T00:00:00Z

A mobilidade térmica de discordância foi investigada em silício puro, floating zone, livre de discordâncias, utilizando medidas de rosetas produzidas por indentação. A mobilidade das discordâncias produzidas em amostras cobertas com camada de óxido crescida termicamente foi comparada com a de superfície não coberta. Um aumento da mobilidade térmica foi encontrado em amostras cobertas. Também foram obtidas informações sobre modificações na estrutura de discordâncias em rosetas relacionadas à anisotropia na dureza. Esse efeito foi encontrado como sendo dependente da temperatura. / The thermal mobility of dislocations was investigated in intrinsic floating zone dislocation free silicon using indentation dislocation rosette (IDR) measurements. The mobility of introduced dislocations in samples covered with a thermal oxide layer was compared with that with a bare surface. An increase on dislocation thermal mobility was found in covered samples. Also information about dislocations pattern structure modifications on IDR related to hardness anisotropy was obtained. This effect was found to be temperature dependent.

No description available.

Molecular dynamics simulations using the Embedded Atom Method were performed to describe the interparticle behavior of two single crystal spherical nickel nanoparticles during compaction based on applied strain rate, particle size, contact angle, and crystal orientation. The evolution of the contact surfaces was analyzed during the molecular dynamics simulation and an investigation of friction effects was conducted at the contact surfaces. The results from the current study were validated by comparing them to previous nanocrystalline research on bulk particle deformation and to previous studies of elasto-plastic contact laws between two macroscale spherical particles. These quantified friction effects give a better understanding of nanoparticle behavior and will be used to develop constitutive equations for larger scale models, such as finite element analysis.

No description available.

Yes / Liquid crystal is a new emerging biomaterial. The physical property of liquid crystal plays a role in supporting the adhesion of cells. Nano and microball indentation techniques were applied to determine the elastic modulus or viscoelasticity of the cholesteryl ester liquid crystals in the culture media. Nano-indentation results (108 ± 19.78 kPa, N = 20) agreed well with the microball indentation (110 ± 19.95 kPa, N = 60) for the liquid crystal samples incubated for 24 hours at 37o C, respectively. However, nanoindentation could not measure the modulus of the liquid crystal (LC) incubated more than 24 hours. This is due to the decreased viscosity of the liquid crystal after immersion in the cell culture media for more than 24 hours. Alternatively, microball indentation was used and the elastic modulus of the LC immersed for 48 hours was found to decrease to 55 ± 9.99 kPa (N = 60). The microball indentation indicated that the LC did not creep after 40 seconds of indentation. However, the elastic modulus of the LC was no longer measurable after 72 hours of incubation due to the lost of elasticity. Microball indentation seemed to be a reliable technique in determining the elastic moduli of the cholesteryl ester liquid crystals. / Science Fund Vot. No. S024 or Project No. 02- 01-13-SF0104 and FRGS Vot. No. 1482 awarded by Malaysia Ministry of Education

Exploring the mechanical properties of soft tissues under compressive loading is crucial for understanding their role in automobile incidents. Soft tissues, which serve as cushions or padding between bone and vehicle interiors, significantly influence contact duration and forces, thereby altering incident kinematics and injury risk assessment. In this investigation, muscle and soft connective tissues from post-mortem human subjects (PMHS) forearms were excised and subjected to compression and indentation testing methods at various rates and strains. Anthropomorphic Test Devices (ATDs) upper extremity foam and vinyl foam composite material surrogate tissues underwent similar testing for comparison. High impact rates simulating those in high-speed car collisions were achieved using a custom-built drop tower. The results revealed substantial differences in stiffness between soft tissues and ATD materials across most loading rates and strains, although some exceptions were noted at higher rates and strains. Indentation and modified Zener models were used to quantify material parameters. The indentation model could characterize human muscle, soft connective tissues and ATD vinyl foam composites, but fell short with ATD foam materials. The Zener model effectively derived material parameters for the tested human tissues but encountered difficulties characterizing both ATD materials. This highlights the need for further refinement to develop a constitutive model for both materials. These findings provide a solid basis for advancing ATD surrogate materials and have broader implications for soft tissue research. Moreover, this work represents a crucial step towards enhancing safety standards in the automotive industry. / Thesis / Master of Science in Biomedical Engineering / Soft tissues are crucial in mitigating impact effects in various loading scenarios, yet their specific roles are complex and poorly understood. Understanding soft tissues' role in these loading scenarios is critical for understanding injury risk tolerances. This study aimed to characterize muscle and soft connective tissue behaviour during compressive loading scenarios using various techniques and modelling approaches. This was done through compressive loading tests on soft tissues and comparing these same tests with data from current crash test dummy surrogate tissues. The results showed that the soft tissues were less stiff than the crash test dummy materials in most scenarios. It was also apparent that different stiffnesses were seen depending on soft connective tissue and muscle tissue composition. This study provides insights into the rate dependence of materials, alongside the relevance of how different compositions affect their loading properties. This characterization also revealed significant discrepancies between the responses of current surrogates and human muscle and soft connective tissues. This work offers valuable observations and data for refining ATD surrogates and enhancing their fidelity in simulating real-world impact scenarios. Such advancements are pivotal for improving safety standards.

Ces travaux de thèse portent sur l’élaboration et la caractérisation de revêtements sol-gel composites ≪ CSG ≫ sur acier inoxydable austénitique AISI 304. L’objectif de la thèse était de mettre au point le procédé d'élaboration et d'étudier les propriétés mécaniques et le comportement tribologique des revêtements. La première partie expérimentale présente l’optimisation des conditions de synthèse d’un sol d’alumine stable et l’influence du traitement thermique du gel sur les propriétés physico-chimiques et thermostructurales. Les paramètres étudiés sont : La stabilité chimique du sol et les conditions de traitement thermique (température et temps). Différentes techniques de caractérisations ont été utilisées pour l'optimisation des paramètres d'élaboration (rhéométrie, ATD/ATG, dilatométrie, DRX, MET, pynométrie hélium). Un dopage au nitrate de fer a permis d'améliorer les conditions de frittage de l'alumine sol-gel grâce à la formation d'une solution solide (Al,Fe)2O3. Cela reste cependant insuffisant pour une application du revêtement sur le substrat acier. La seconde partie concerne l’élaboration et la caractérisation mécanique de revêtements sol-gel composites ≪ CSG ≫ charges de particules d’α-Al2O3 et de h-BN. Ce procédé a permis d'obtenir par dip-coating des dépôts monocouches de 8,5 micromètres environ avec des taux de charge de 90% volumique. Cependant, un tel taux de charge provoque la création d’une porosité importante. Les couches CSG traitées thermiquement à 750°C ont par la suite été caractérisées mécaniquement par indentation instrumentée. Les résultats obtenus ont montré une trop faible dureté des couches pour pouvoir améliorer la résistance à l'usure. La dernière partie de la thèse concerne le renforcement des revêtements CSG après traitement à l'acide phosphorique et traitement thermique à 400°C. La formation de liaisons phosphates entre les grains d'alumine renforce l'architecture du composite qui est note CB-CSG ≪ Chemically Bonded Composite Sol-Gel ≫. Des essais d'indentation instrumentée montrent, pour des revêtements CB-CSG charges d’alumine, une amélioration de la dureté par rapport au substrat en acier. Des essais de frottements secs en configuration bille sur plan montrent une augmentation de la résistance aux frottements secs d’un facteur 5 et une diminution du coefficient de frottement par rapport au substrat. L’influence du nitrure de bore hexagonal dans les couches CB-CSG en plus de l'alumine a été étudiée en particulier en ce qui concerne les propriétés mécaniques et tribologiques. / This thesis focuses on the elaboration and the characterization of composite sol-gel coatings “CSG” on austenitic stainless steelAISI 304. The aim of the thesis is to develop the process and to study the mechanical properties and tribological behavior of thecoatings. The first experimental part presents the optimization of the synthesis conditions of a stable alumina sol and the influence of the thermal treatment of the gel on the physic-chemical and thermostructural properties. The studied parameters are: The chemical stability of the sol and the thermal treatment conditions (temperature and time). Various characterization techniques are used in order to optimize the elaboration parameters (rheometry, DTA / TGA, dilatometry, XRD, TEM, helium pycnometry). A Doping with iron nitrate has improved the sintering conditions of the sol-gel alumina through the formation of a solid solution (Al,Fe)2O3. However, this remains insufficient for an application of the coating on the steel substrate. The second part concerns the elaboration and the mechanical characterization of composite sol-gel coatings "CSG" filled with particles of α-Al2O3 and h-BN. This process enables the deposition by dip coating of monolayer coatings of 8.5 micrometers thickness with fill rate of 90% by volume. However, such filler content produces a high porosity. The CSG layers thermally treated at 750°C have been mechanically characterized by instrumented indentation. The results shown to low hardnesses in order to improve the wear resistance. The last part of the work presents the strengthening of CSG coatings with a treatment with phosphoric acid followed by a thermal treatment at 400°C. The formation of phosphate bonds between the alumina grains enhances the architecture of the composite which is denoted CB-CSG "Chemically Bonded Composite Sol-Gel". Instrumented indentation tests show, for CBCSG coatings filled with alumina, an improvement of hardness compared to the steel substrate. Dry friction tests, with ball on disc configuration, show an increase of resistance to dry friction by a factor of 5 and a decrease of the coefficient of friction relatively to the substrate. The influence of the hexagonal boron nitride and of the alumina in the CB-CSG layers on the mechanical and the tribological properties are particularly studied.

Le travail présenté dans cette thèse est consacré à la précipitation interphase dans les aciers microalliés au vanadium. Il s’agit principalement de mieux comprendre l’évolution des microstructures et des propriétés mécaniques résultantes à partir d’une double approche expérimentale et de modélisation. Les analyses effectuées conjointement en Microscopie Electronique en Transmission et en nanoindentation ont permis de mieux cerner les relations qui existent entre les paramètres microstructuraux de la précipitation interphase (taille moyenne des carbures, distances moyenne entre carbures et entre feuillets, morphologie des carbures) et les modifications de propriétés mécaniques locales induites dans les aciers à très haute résistance. Par ailleurs, nous avons développé un modèle original qui couple les cinétiques de transformation de phases à celle de la précipitation interphase. Ce modèle permet de décrire l’évolution des paramètres microstructuraux et les résultats obtenus sont en très bon accord avec les résultats expérimentaux. / The present thesis gives an overview of carbide aggregates (interphase precipitation and carbide fiber) in vanadium-alloyed steels, covering the aspects of microstructure, modeling, and mechanical properties. The microstructural features of different carbide aggregates by the use of microscopies, and the transition of carbide morphologies is discussed. A new model considering the ledge mechanism as well as austenite decomposition is subsequently proposed according to the observed microstructure. The sheet spacing, particle spacing, and interface velocity, can be calculated and show good agreements with experimental data. Finally, the effect of interphase-precipitated carbide distribution (sheet spacing, particle spacing, and carbide radius) on Orowan strengthening contribution is examined by nano-indentation. By the virtue of small indenter, the mechanical properties of single ferrite grain are able to be extracted.Keyword: