Le travail s’intéresse aux effets de l’histoire de chargement sur le comportement et la durée de vie en fatigue de deux nuances (THYSSEN et CLI)d’un acier inoxydable austénitique 304L à la température ambiante. Les essais ont été réalisés en utilisant deux catégories d’éprouvettes. Les éprouvettes de la première catégorie (vierges) ont été soumises à des essais classiques de fatigue,alors que celles de la deuxième ont subi, avant les essais de fatigue, un pré-écrouissage monotone ou cyclique en déformation imposée. Les éprouvettes vierges manifestent un adoucissement cyclique suivi d’un durcissement cyclique alors que les éprouvettes pré-écrouies ne présentent qu’un durcissement cyclique. Les résultats montrent une grande influence du pré-écrouissage qui semble bénéfique en contrainte imposée, mais néfaste en déformation imposée,même en présence d'une contrainte moyenne de compression. Ces résultats sont discutés en termes d'évolution cyclique du module d'élasticité, des écrouissages isotropes et cinématiques, et de la densité d’énergie absorbées par cycle, dans différentes configurations : avec ou sans pré-écrouissage, en contrainte ou déformation imposées... / This study deals with the effect of the loading history on the cyclic behavior and the fatigue life of two kinds (THYSSEN and CLI) of 304L stainless steel at room temperature. The experiments have been performed using two specimens’ categories. The first one (virgin) has been submitted to only classical fatigue tests while in the second category, prior to the fatigue test, the specimen is subjected to a pre-hardening process under either monotonic or cyclic strain control. Cyclic softening followed by cyclic hardening are observed for the virgin specimens while only cyclic softening is exhibited by the pre-hardened specimens. The obtained results show that fatigue life is strongly influenced by the pre-hardening: it seems beneficial under stress control but detrimental under strain control, even in the presence of a compressive mean stress. The results are discussed regarding the cyclic evolution of the elastic modulus aswell as the isotropic and kinematic parts of the strain hardening, and strain energy density per cycle, in different configurations: with or without prehardening,stress or strain control...

Our purpose was to investigate the influence of in vitro oocyte aging on fertilization and subsequent embryonic development following subzonal sperm injection with reference to spontaneous zona hardening in the mouse.

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<p> The effect of strain hardening rate and material strength on the development of surface roughness in AA6111 was investigated. No measurable change in the rate of roughening, or in the surface morphology was observed due to altering the strain hardening rate by using different test temperatures. Changing the material strength and strain hardening rate by altering the precipitation state also gave no significant change in either roughening rate or morphology with respect to strain. The development of surface roughness is also independent of strain history. Samples subjected to an intermediate polish after 20% true strain resumed roughening at the same rate regardless of amount of previous tensile strain. The development of surface roughness is dependent on only the strain level to which the sheet is deformed. The surface morphology seems to be controlled by the combination and distribution of texture components on the surface. The rate of roughening is grain size dependent and the surface grain size may provide a key to controlling roughening. </p> / Thesis / Master of Applied Science (MASc)

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Causes for the differences in precipitation morphology observed and investigation. / Master of Science

Existing specifications for asphalt cement employ insufficient aging and conditioning times prior to testing and low strains during the actual test which are insufficient to predict asphalt performance, especially if the materials are modified with additives such as those used for warm mix technology. However, slightly modified protocols, like increasing the conditioning time in the bending beam rheometer (BBR) test and increasing the aging duration in the pressure aging vessel (PAV), predict asphalt performance better than the current Superpave™ specification. These improved protocols are published as new test standards through the collaborative effort between the Ontario Ministry of Transportation and Queen’s University. In this study, the effects of warm mix and other additives on rheological, aging and failure properties are investigated. The properties are measured by regular tests and by modified protocols. The latter include the extended BBR test (LS-308) and the double-edge-notched tension (DENT) test (LS-299). Changes in ductile strain tolerance within base asphalts due to the various additives as measured with the DENT test were found to be very significant. The DENT results like essential work of fracture, we, plastic work of fracture term, βwp, and critical crack tip opening displacement, CTOD, are usually helped to correlate with the cracking distress survey results of the pavement in service. The addition of amide and polyethylene waxes risks increasing the cracking susceptibility in the pavement. They show a negative effect on strain tolerance in the ductile state, which is likely to show up as premature and/or excessive cracking in service which is similar to their physical hardening behavior from low temperature grading and extended BBR testing. / Thesis (Master, Chemistry) -- Queen's University, 2013-02-26 11:10:41.08

Environmental stress cracking (ESC) is one of the main, and probably the most common, failure mechanisms involved in polymer fractures. This type of failure is critically important as it occurs suddenly, without any visible pre-fracture deformation. Such failure can be catastrophic and costly in cases where structural integrity is required. In polyethylene (PE), ESC occurs through a slow crack growth mechanism. Cracks initiate from stress-concentrated imperfections, propagate through the bulk of PE, and ultimately result in a brittle fracture. In order to predict the environmental stress cracking resistance (ESCR) of PE, it is necessary to fully understand the molecular structure of the resin. In this thesis, attempts were made to find relationships between molecular structure characteristics and material responses, mainly inter-lamellar entanglements and strain hardening behaviour of PE resins, through mechanical and rheological experiments. Inter-lamellar entanglements are believed to be the main factor controlling slow crack growth of PE. Extent of entanglements and entanglement efficiency were investigated by monitoring the strain hardening behaviour of PE resins in the solid state through a uniaxial tensile test, and in the melt state, through extensional rheometry. ESCR is usually assessed by unreliable and time consuming testing methods such as the notch constant load test (NCLT) on notched PE specimens in the presence of an aggressive fluid and elevated temperatures. In this thesis, a practical, yet reliable, tensile test was developed for the evaluation and prediction of ESCR. The developed test offers a more reliable and consistent ESCR picture without the drawbacks of the subjective notching process and presence of aggressive fluids. Through this test, a factor called ???corrected hardening stiffness (cHS)??? was developed, which can easily be used for a relative ranking of ESCR of different PE resins. Studies were next extended to the melt state via shear and extensional rheometry. Through studies in the shear mode, a molecular weight-normalized average characteristic relaxation time (??N) was found to be efficient in predicting the extent of chain entanglements in resins. This provided a potential melt indicator for a relative measure of ESCR, for linear low density polyethylene (LLDPE), with different short chain branching levels. Extensional studies were conducted to evaluate the strain hardening behaviour in the melt state. An inverse correlation was obtained between ESCR and the melt strain hardening coefficient (MSHC), found from Sentmanat Extensional Rheometry (SER). This indicated an inverse relationship between ESCR and chain extensibility in the melt. In addition, a new factor called ???melt hardening stiffness (mHS)??? was developed from the slope of a stress-strain line, obtained from SER. This factor, analogous to cHS, can be used for a practical and reliable ranking of ESCR of PEs. ESCR is usually associated with classical crystalline phase property indicators, such as crystallinity and lamella thickness. In this thesis, the effect of processing and post processing temperature on the extent of inter-lamellar entanglements were investigated, evaluated, and correlated to ESCR. Also, analysis of the lamella surface area (LSA) was pursued since LSA reflects changes in phase interconnectivity more precisely. The focus of this part of the study was on the effect of temperature on LSA to identify the optimum processing and post-processing conditions which yield a higher LSA. It was reasonable to presume that PE with larger lamella lateral surface areas will have more inter-lamellar entanglements, hence higher ESCR. Finally, a well-controlled ultraviolet (UV) photoinitiated reactive extrusion (REX) process was developed for selective formation of long chain branches in the PE structure. This was conducted to impose restrictions against stretching of the polymer chain, which consequently enhanced ESCR.

This work deals with the assessment of the influence of low-temperature treatment on the structure and properties of casehardened surface layer of parts. The objective was to assess whether low-temperature treatment is sufficient, insufficient, or unnecessary for the given purpose. Gears which form a part of Zetor tractors gear boxes were used as samples. Thirteen pairs of frozen and non-frozen samples were used; they were taken from production batches throughout 2007, their hardness was assessed and furthermore, the experiment itself, freezing casehardened and hardened samples to different temperatures reaching as low as -196°C, was carried out. A moderate increase in hardness was registered with the majority of the frozen samples, which proved the effectiveness of the low-temperature treatment.