Amorphous Mg-Cu-Y metallic glasses are established by density functional theory and simulated annealing method in this study. The mechanical properties of amorphous Mg-Cu-Y metallic glasses are investigated by molecular statics simulations for the nano-indentation and the nano-scratch process. In this study, some potential energy parameters are obtained by fitting for describing the Mg-Cu-Y system. The bulk modulus, the Young¡¦s modulus and X-ray structure of the Mg-Cu-Y system are calculated. Our results are within 10% error compared with experimental values, which prove the correctness of fitted potential parameters. For the cases of nanoindentations, the indentation force-displacement and the influenced depth are calculated. The mechanical properties are obtained are close to experimental results. The both ¡§slip vector¡¨ and Honeycutt-Andemen index (HA index) parameters are also used to study the deformation behavior and bond-type of a group of atoms. Our results indicate that the influenced depths can be affected by the tip indentation and the gather of copper atoms. The gather of copper atoms can provide the resistance and strengthen the mechanical properties of Mg-Cu-Y material. On the other hand, our results indicate that the amorphous structure of Mg-Cu-Y metallic glasses cannot be transferred to crystal structure during nano-indentation process by analysis of HA index. For the cases of nano-scratch, two different scratch depth (5Å and 15Å) are investigated to understand the understand the depth effect. the scratch force-displacement curve is also obtained. As the same with nano-indentation results, the scratch force will increase because the gather of copper atoms and provide the resistance.

This thesis presents the research results of a correlation and model based on nano and macroindentation hardness measurements. The materials used to develop and test the correlation include bulk tantalum and O1 tool steel. Following the literature review and a detailed description of the experimental techniques, the results of the nanoindentation hardness measurements are presented. After applying the methods and correlation recommended here, the results should give an accurate value of hardness in the Vickers scale for microstructural features that are too small to be precisely and exclusively measured using the traditional macroindentation hardness technique. The phenomena and influential factors in nanoindentation hardness testing are also discussed. These phenomena and theories are consistent with the microstructural behavior predicted in the Nix and Gao model for mechanism-based strain gradients. Implementing the correlation factors and/or correlation curve, accurate results can be found for metals over a broad hardness range. Initially, this research may impact the pipeline division of the petroleum industry by providing a correlation to the Vickers scale for nanoindentation testing of microstructural features. This thesis may also provide a research methodology to develop hardness correlations for materials other than metals. This thesis consists of eight chapters. Following an introduction in Chapter I, the research motivations and objectives are highlighted in Chapter II. Chapter III explains the multi-scale indentation techniques used in this thesis and Chapter IV presents the materials preparation techniques used. Then, the results are presented in Chapter V, followed by the factors affecting nanoindentation hardness in Chapter VI. Finally, Chapters VII and VIII reveal the indentation contact analysis, correlation, and conclusions of this research, respectively.

Many soft food materials, including vegetable shortening, exhibit complex rheological behaviour with properties that resemble those of a solid and a liquid simultaneously. The fundamental parameters used to describe the rheological response of vegetable shortening were obtained from uniaxial compression tests, including monotonic and cyclic compression, as well as creep and stress relaxation tests. The fundamental parameters obtained from the various compression tests were then used in two mechanical models (viscoelastic and elasto-visco-plastic) to predict the compression and conical indentation response of vegetable shortening. The accuracy of the two models was studied with the help of the commercially available finite element analysis software package Abaqus. It was determined that the viscoelastic model was not suitable for the prediction of the rheological response of shortening. On the other hand, the proposed elasto-visco-plastic model predicted with reasonable accuracy the uniaxial compression and indentation experimental response of vegetable shortening.

Many soft food materials, including vegetable shortening, exhibit complex rheological behaviour with properties that resemble those of a solid and a liquid simultaneously. The fundamental parameters used to describe the rheological response of vegetable shortening were obtained from uniaxial compression tests, including monotonic and cyclic compression, as well as creep and stress relaxation tests. The fundamental parameters obtained from the various compression tests were then used in two mechanical models (viscoelastic and elasto-visco-plastic) to predict the compression and conical indentation response of vegetable shortening. The accuracy of the two models was studied with the help of the commercially available finite element analysis software package Abaqus. It was determined that the viscoelastic model was not suitable for the prediction of the rheological response of shortening. On the other hand, the proposed elasto-visco-plastic model predicted with reasonable accuracy the uniaxial compression and indentation experimental response of vegetable shortening.

While inelastic mechanical behaviour of crystalline materials is well-understood in terms of lattice defects, bulk metallic glasses (BMGs) pose significant challenges in this respect due to their disordered structure. They can be produced by rapid cooling from the liquid state (among other technique) and, thus can be frozen as vitreous solids. Due to the absence of a long-range order in atomic structure and a lack of defects such as dislocations, BMGs generally show unique mechanical properties such as high strength and elastic limit, as well as good fracture toughness and corrosion resistance. Typically, inorganic glasses are brittle at room temperature, showing a smooth fracture surface as a results of mode-I brittle fracture. At small scale, it was well documented that inelastic deformation of bulk metallic glasses is localised in thin shear bands. So, in order to understand deformation mechanisms of BMGs comprehensively, it is necessary to investigate formation of shear bands and related deformation process. In this thesis, a history of development of BMGs is presented, followed by a review of fundamental mechanisms of their deformation.

No description available.

Advanced high strength steel (AHSS) provides a lightweight material solution in response to the stringent regulation on fuel economy and greenhouse gas emissions in the automotive industry. Dual phase (DP) steels that consist of a hard martensite phase embedded in a soft ferrite matrix are the most widely used AHSS due to their simple microstructure, robust thermo-mechanical processing and attractive mechanical properties. However, DP steels are prone to deform heterogeneously with strong strain partitioning between phases. The addition of Vanadium in DP steels can form nano-precipitates of vanadium carbonitrides (V (C,N)) that strengthen the ferrite and thus reduce the strain partitioning. This study considered the influence of V (C,N) on the deformation and damage behavior of ferrite-martensite DP1300 steels at the microscopic level. The hardness of the embedded ferrite and martensite regions are determined through nano-hardness testing. In-situ uniaxial tension tests were conducted on DP steels with similar martensite volume fractions within a scanning electron microscope (SEM) chamber. Microscopic-digital image correlation (µDIC) was then employed to analyze the local strain partitioning between ferrite and martensite. Local damage events such as void formation at ferrite martensite island interfaces and in the martensite islands were observed and rationalized with the µDIC results. X-ray computed tomography (XCT) were conducted to quantitatively analyze the microstructure damage. It was found that vanadium addition helps refine the microstructure and improve mechanical compatibility between the two phases. The overall ductility of the steel is enhanced especially in terms of post-uniform elongation and true strain to fracture. / Thesis / Master of Applied Science (MASc)

Doctor of Philosophy / Civil Engineering / Robert J. Peterman / A study was conducted to determine the effect of different concrete properties and prestressing steel indentation types on development length and flexural capacity of pretensioned members. Wires and strands commonly used in the manufacturing of prestressed concrete railroad ties worldwide were selected for the study. Thirteen different 5.32-mm-diameter prestressing wire types and six different strands (four, seven-wire strands and two, three-wire strands) were used to cast prisms with a square cross section. The ratio of concrete to prestressed steel in the test prism’s cross section was representable of typical concrete railroad ties. Thus, geometrical and mechanical properties of test prisms were representative of actual ties in the railroad industry. To understand the effect of concrete-release strengths and slumps on development length, all parameters were kept constant in the prisms except concrete-release strength and slump. To manufacture prisms with different release strengths, all four wires/strands were pulled and detensioned gradually when the concrete compressive strength reached 3500 (24.13 MPa), 4500 (31.03 MPa), and 6000 (41.37 MPa) psi. To determine the effect of different slumps on development length, prisms with different slumps of 3 in. (7.6 cm), 6 in. (15.2 cm), and 9 in. (22.9 cm) were manufactured and all other parameters were kept constant in prisms. All prisms were tested in three-point bending at different spans to obtain estimations of development length based on type of reinforcement, concrete-release strength, and concrete slump. Lastly, a design equation was developed based on experimental data for prediction of development length. In the last phase of load tests, cyclic-loading tests were conducted on the prisms manufactured with wires to evaluate the bond performance of wires with different indentation types under cyclic loading. A total of 210 load tests, including 14 cyclic tests, were conducted. The monotonic-load tests revealed a large difference in the development length of pretensioned concrete members manufactured with different wire/strand types and different concrete-release strengths. Also, the cyclic-load tests revealed a significant difference in bond performance of different wire types under cyclic loading compared to monotonic loading.

L’indentation instrumentée est largement utilisée pour la détermination des propriétés mécaniques des matériaux, principalement la dureté et le module d’élasticité. Pour obtenir des données fiables, plusieurs corrections comme la prise en compte du défaut de pointe et la complaisance de l’instrument doivent être apportées dans la méthodologie d’analyse des données de l’essai. Malgré tout, ces corrections ne suffisent plus pour la caractérisation de matériaux fragiles et poreux, qu’ils soient sous une forme massive ou de revêtement. En effet, d’autres sources d’erreurs peuvent provenir de la fragilité de ces matériaux, mais aussi de la représentativité des mesures locales dans le cas des matériaux hétérogènes, ou de l'influence du substrat dans le cas des revêtements. Pour limiter ces effets, l’indenteur Knoop semble être un bon candidat car, à charge équivalente, sa surface de contact est plus grande et la profondeur d’indentation plus faible. Toutefois, par rapport aux indenteurs habituels, le retour élastique du matériau au voisinage de l'empreinte Knoop, qui doit être pris en compte dans les calculs des propriétés, n’est pas bien connu. Ceci constitue donc un frein à son utilisation. C’est pourquoi, nous proposons d’adapter la méthodologie conventionnelle proposée par Oliver et Pharr pour obtenir des résultats fiables par indentation Knoop. Pour atteindre cet objectif, nous analysons d’abord des résultats obtenus par indentation de différents matériaux céramiques denses en comparant les indentations Knoop et Vickers, ce dernier étant utilisé comme référence. Tout d’abord, nous analysons le retour élastique en indentation Knoop et nous montrons qu’il est possible de retrouver les mêmes valeurs qu’en indentation Vickers en intégrant un facteur correctif lié simplement à des grandeurs géométriques de l’empreinte. Cette approche est valable qu’il s’agisse de la détermination du module d’élasticité ou de la dureté. Toutefois, pour cette dernière propriété, il est nécessaire de bien préciser la définition utilisée pour son calcul. Nous en justifions le choix. Ensuite nous appliquons la méthodologie d’analyse ainsi établie pour l’étude de la réponse mécanique des matériaux poreux sous forme massive et de revêtement où non seulement le paramètre de porosité joue un rôle important sur la réponse du matériau, mais aussi son hétérogénéité, sa rugosité et son épaisseur. De manière générale, nous montrons que l’indenteur Knoop présente un intérêt certain par rapport aux indenteurs habituels, tout au moins dans le cas des céramiques. / Instrumented indentation is widely used for the assessment of mechanical properties, mainly hardness and elastic modulus. In order to obtain reliable results, analysis methodology has to refer several corrections, such as tip defect and frame compliance. However, these corrections are insufficient for the characterization of brittle and porous materials, whether bulk or coatings. Not only brittleness but also local surrounding in the case of heterogeneous materials and substrate influence in the case of coatings raise error concerns. To limit these unwanted effects, the Knoop indenter appears to be a favorable candidate because of the larger contact area and lower indentation depth at equivalent loads. However, compared to other commonly used indenters, radial elastic recovery near Knoop indent that has to be taken into account in the analysis methodology, is not well known. This constitutes therefore an obstacle for its use. Thereof, we propose to adapt the conventional methodology proposed by Oliver and Pharr to obtain reliable results with Knoop indentation. To achieve this purpose, we analyze the indentation data of different dense ceramic materials by comparing Knoop and Vickers indentations, this latter being used as a reference. First, we analyze the elastic recovery using Knoop indenter. We show that correlation to Vickers indentation results is possible using a geometric correction factor. This approach is valid for the determination of elastic modulus and hardness. However, for the latter property, it is necessary to specify the definition used for its calculation. The established analysis methodology was applied for studying the mechanical response of porous bulk materials and coatings, with respect to material porosity, roughness and thickness. It was confirmed that Knoop indenter may be favorable compared to the commonly used indenters, at least in the case of ceramics.

Ce travail de thèse combine des approches expérimentales et théoriques visant à caractériser les propriétés mécaniques et de durabilité des bétons à base de granulats recyclés. La première partie est consacrée à la quantification de l'effet des granulats recyclés sur les propriétés mécaniques et de durabilité de ces bétons. Les résultats montrent que les propriétés mécaniques et de durabilité des bétons à base de granulats recyclés sont sensibles non seulement aux propriétés physiques des granulats recyclés mais aussi à leur quantité au sein de la microstructure. Par ailleurs, une caractérisation des propriétés mécaniques locales grâce aux essais de nano indentation et micro indentation a aussi été entreprise; ce qui a permis d'avoir accès aux propriétés mécaniques des phases telles que les zones d'interface ou encore l'ancien mortier. La deuxième partie est une approche consacrée à l'établissement des modèles multi-échelles en mesure de rendre compte des propriétés macroscopiques (mécanique et de diffusion) des bétons à base de granulats de démolition en tirant profit des informations recueillies sur la microstructure (observation au microscope, nano et micro indentation,...). Une prise en compte du caractère complexe des granulats recyclés a aussi été abordée dans ce développement théorique. Enfin, une comparaison des résultats des modèles avec ceux expérimentaux est présentée puis discutée dans ce travail / This thesis combines experimental and theoretical approaches to characterize the mechanical and durability properties of recycled aggregate concretes (RAC). The first part of the work is devoted to the quantification of the impact of recycled concrete aggregates on the mechanical and durability properties of RAC. The results show that mechanical and durability properties of recycled aggregate concretes depend not only on the physical properties of recycled concrete aggregates but also on their quantity in the microstructure. Furthermore, statistical indentation technique is used to capture the local mechanical properties of phases in the microstructure of RAC such as the interfacial transition zones and the attached mortar. The second part of this study deals with the multi-scale modeling of the mechanical and the durability properties of RAC. The main purpose of this theoretical work is to establish models capable to predict the macroscopic behaviour based on the available information on the microstructure (obtained by optical microscopy or through indentation technique). The established models take into account the complex structure of the recycled concrete aggregates. Finally, the results of the models are compared with experimental data for discussion