Traditional tribology is based on the surface with random micro structures due to limitations of manufacturing technology. The modern manufacturing technology now promises to fabricate surfaces with regular micro structures (or asperities). The word asperity refers to a single physical entity on the surface of a material, contributing to a concept called roughness in traditional tribology. Regular asperity surfaces imply that all asperities on the surface of a material have the same shape and size, and a deterministic distribution over the surface. The emergence of regular asperity surfaces will have a transformative impact to the discipline of tribology.<p> The overall objective of this thesis is to study how the regular asperity would affect the tribological behavior. Specifically, this thesis develops a computational model to demonstrate and characterize the effect of the surface with regular anisotropic asperities (RAA) on the directional friction behavior when the surface is in a fully lubricated state. By directional friction, it is meant that friction force changes its magnitude with the change of the relative motion direction. By anisotropic asperity, it is meant that the geometry of the asperity is not symmetrical along the motion direction.<p> This thesis presents a detailed development of the computational model by employing computational fluid dynamics (CFD) techniques. In particular, the model takes the Navier-Stokes (NS) equation as a governing equation and the Half-Sommerfeld Condition (HSC) to represent fluid behavior in the cavitation region; as such the model is named NS-HSC for short. Verification of the NS-HSC model is conducted with the information available in literature. A theory is proposed to explain the relationship between directional friction behavior and specific RAA structures. The thesis concludes: (1) the NS-HSC model is more accurate than the existing model in the literature and can be used to predict directional friction behavior and to design RAA surfaces, and (2) the proposed theory is excellent consistent with the NS-HSC model and thus useful to analysis and design of RAA surfaces for directional friction.<p> The major contributions of this thesis are: (1) the first model in the field of tribology to predict the directional friction behavior for RAA surfaces under a fully lubricated status, (2) the first investigation, in the field of CFD, into combining the NS and HSC for modeling a laminar flow with cavitation, and (3) the first theory in the field of tribology for directional friction on fully lubricated RAA surfaces.

Aim of the study: The aim of this study was to measure the effects of a specific technique used when assisting vaginal delivery and intended to decrease anal sphincter ruptures. After measuring the effects, the direct costs of a rupture were calculated and finally the cost impact of the intervention was evaluated. Data and model: Data from deliveries before the intervention, from 2004, and after the intervention, from 2008, were used and a pre-test – post-test evaluation design was applied. The dependent variable was the presence or absence of a rupture and because the variable is binary a logit model was used. The independent variables consisted of twelve different factors considered to affect the number of ruptures. When only accounting for ruptures alone 123 of 2900 deliveries resulted in a sphincter ruptures which equals 4.24% of the total amount of deliveries. Results: When not controlling for any of the independent variables, the risk of getting a rupture decreased by 3.8 percentage points when using the method while assisting a delivery. On the other hand, when controlling for all of the independent variables and the use of the method, the risk of getting a rupture decreased by 2.5 percentage points, from 4.24% to 1.74%. Two different models were tested, one with the variable weeks and one without the same variable, due to the presence of correlation in the model. The total cost of ruptures for a year was calculated as $84,429,254 without the implementation of the method and $34,647,854 with the implementation. Total cost savings for society with the implementation of the method would then be $49,677,045. Conclusions: Implementation of the method is highly recommendable for both society and the women involved. Not only does the number of ruptures decrease due to the method but also the costs for society decreases dramatically.

The goal of this research was to determine whether precast prestressed bridge elements with congested reinforcement could be cast using self-consolidating concrete (SCC) without vibration and yet comply with all parameters of strength, no honeycombing, and void-free surface finish. Eight wall panels and eight BT-72 13-ft long girder sections were fabricated in two precast plants. A qualitative and quantitative evaluation of the surface finish, and homogeneity of the concrete throughout the specimens was performed. Strength, creep, shrinkage and chloride permeability of the SCC field mixes were investigated. Good quality SCC mixes were produced for the walls and the BT-72 girder sections, which completely filled the specimens without the need of internal or external vibration, and resulted in a superior surface finish and a homogenous distribution of the aggregate throughout the section.

Texte remanié de: Th. doct.--Droit privé--Lille 2, 2000. / Bibliogr. p. 197-228.

Thèse doctorat : Mécanique : Villeurbanne, INSA : 2006. / Titre provenant de l'écran-titre. Bibliogr. p. 157-168.

Thèse doctorat : Mécanique : Villeurbanne, INSA : 2007. / Titre provenant de l'écran-titre. Bibliogr. p. [179]-187.

Thèse de doctorat : Mécanique : Metz : 2009. / Titre provenant de l'écran-titre. Notes bibliogr.

A numerical model that predicts high temperature pressure vessel rupture was developed. The finite element method of analysis was used to determine the effects that various parameters had on pressure vessel failure. The work was concerned with 500, 1000 and 33000 US gallon pressure vessels made of SA 455 steel. Experimental pressure vessel fire tests have shown that vessel rupture in a fully engulfing fire can occur in less than 30 minutes. This experimental work was used both to validate the numerical results as well as to provide important vessel temperature distribution information. Due to the fact that SA 455 steel is not meant for high temperature applications, there was little published high temperature material data. Therefore, elevated temperature tensile tests and creep rupture tests were performed to measure needed material properties. Creep and creep damage constants were calculated from SA 455 steel’s creep rupture data. The Kachanov One-State Variable technique and the MPC Omega method were the creep damage techniques chosen to predict SA 455 steel’s high temperature time-dependent behaviour. The specimens used in the mechanical testing were modeled to numerically predict the creep rupture behaviour measured in the lab. An extensive comparison between the experimental and numerical uniaxial creep rupture results revealed that both techniques could adequately predict failure times at all tested conditions; however, the MPC Omega method was generally more accurate at predicting creep failure strains. The comparison also showed that the MPC Omega method was more numerically stable than the One-State Variable technique when analyzing SA 455 steel’s creep rupture. The creep models were modified to account for multiaxial states of stress and were used to analyze the high temperature failure of pressure vessels. The various parameters considered included pressure vessel dimensions, fire type (fully engulfing or local impingement), peak wall temperature and internal pressure. The objective of these analyses was to gain a better understanding of the structural failure of pressure vessels exposed to various accidental fire conditions. The numerical results of rupture time and geometry of failure region were shown to agree with experimental fire tests. From the fully engulfing fire numerical analyses, it was shown that pressure vessels with a smaller length to diameter ratio and a larger thickness to diameter ratio were inherently safer. It was also shown that as the heated area was reduced, the failure time increased for the same internal pressure and peak wall temperature. Therefore, fully engulfing fires produced more structurally unstable conditions in pressure vessels then local fire impingements. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2008-07-04 10:55:32.008

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