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La sensibilité à l’hydrogène d’un acier de type S690QL a été étudiée par une approche locale de la rupture. Des essais de fatigue ont été réalisés à l’air et en milieu salin sous protection cathodique sur des éprouvettes micro-entaillées. La fissure a été contrôlée en cours d’essai par une méthode de suivi électrique. La réponse mécanique du matériau en avant de l’entaille a été simulée par calculs par éléments finis.Les mécanismes de fatigue ont été étudiés par une méthode permettant d’isoler une contrainte interne et deux composantes de la contrainte effective, activée et non-activée thermiquement. L’effet de l’hydrogène sur ces contraintes a également été étudié.Pour comprendre le phénomène de piégeage de l’hydrogène dans la microstructure de cet acier, des tests de perméation électrochimique et de désorption thermique ont été réalisés. Les paramètres expérimentaux ainsi déterminés sont utilisés dans un modèle phénoménologique de la diffusion. Il a été développé pour simuler la répartition locale de l’hydrogène sur des géométries complexes.Les résultats montrent une forte dépendance de l’amorçage de la fissure avec l’accumulation de déformation plastique. Pour les essais de fatigue réalisés sur les éprouvettes entaillées, il ressort que le piégeage dans le champ élastique des dislocations est le phénomène prépondérant dans le mécanisme de fragilisation. Dans le cas d’éprouvettes lisses sollicitées en fatigue oligocyclique, le piégeage dans les murs de cellules de dislocations est majoritaire et l’amorçage de la fissure est certainement localisé sur ces défauts. L’hydrogène affecte également les deux composantes, thermique et athermique, de la contrainte effective. / The sensitivity to hydrogen embrittlement of S690QL steels is studied by local approach to fracture. Fatigue tests in air and in saline solution under cathodic protection are performed on micro-notched specimens. Crack is monitored by direct current potential drop method. The mechanical response of the material at the notch-tip is simulated by finite elements calculations.Fatigue mechanisms are investigated by a decomposition method of the flow stress to extract internal stress and the thermal and athermal components of the effective stress. Hydrogen effects on these stresses are also studied.Hydrogen trapping in the microstructure is investigated using electrochemical permeation tests and thermal desorption spectrometry. A phenomenological model is developed thanks to experimental results. This model is able to simulate the local hydrogen concentration in samples with complex geometry.Our results show that crack initiation is highly dependent on the plastic strain accumulation. For fatigue tests on micro-notched specimens, hydrogen trapping in dislocations elastic field is the predominant phenomena in the embrittlement mechanism. For smooth specimens under low cycle fatigue testing, hydrogen trapping in dislocations cells walls is significant and crack initiation is probably localized in this microstructural defect. Both components of the effective stress are also influenced by hydrogen.

Bakgrund: Fatigue (hjärntrötthet) är ett tillstånd som kan uppkomma till följd av exempelvis en stroke och förklaras som en extrem trötthet som inte går att vila bort. Detta är ett tillstånd som många gånger kan upplevas som ett problem efter en stroke. Syfte: Att belysa hur det är att leva med fatigue till följd av stroke. Metod: En litteraturstudie bestående av nio vetenskapliga artiklar med kvalitativ ansats genomfördes för att besvara syftet. Artiklarna kvalitetsgranskades och en innehållsanalys av artiklarnas resultat utfördes. Resultat: Post-stroke fatigue kunde upplevas påfrestande och inverkade negativt på livet. Sömn och vila tog upp mycket tid och nya rutiner krävdes för att orka med det vardagliga livet. Det blev svårare att upprätthålla samma sociala liv som tidigare. Informationen som gavs till patienterna upplevdes som bristfällig och vårdpersonalen kunde uppfattas okunniga om fatigue till följd av stroke. De personer som hade en ökad kunskap om fatigue kunde lättare hantera och anpassa sig till situationen. Slutsats: Att arbeta personcentrerat kan underlätta för att upptäcka vårdbehovet av fatigue. För att upptäcka vårdbehovet kan en större kunskap hos sjuksköterskorna behövas än vad patienterna upplever att de har. Kunskapen om post-stroke fatigue kan utökas genom att implementera det i sjuksköterskeutbildningen.

Previous research has examined a variety of behavioural effects, thought to stem from mental exhaustion, following the prior use of inhibitory control. Here we attempt to examine whether such effects are apparent in unconscious behaviours. Chapter 1 demonstrates no effect of prior use of inhibitory control on subsequent susceptibility to subliminal priming of neutral (Experiment 1) and reward (Experiment 2) terms. Chapter 2 explores whether the prior use of inhibitory control influences the degree of susceptibility to an alternative source of influence, hypnotic induction, and provides the novel finding that inhibitory impairment does not affect hypnotic response. Chapter 3 utilises behavioural and fMRI imaging data to examine changes in a conscious facet of human experience often moderated by unconscious influences: emotion regulation. The results support a period of increased mood lability following a challenging inhibitory control task. However, we were unable to provide evidence of any underlying change in cortical activation and connectivity. Finally, Chapter 4 investigates whether this heightened mood lability following prior inhibitory control would also be mirrored in ratings of emotion attributed to positive and negatively valenced images (Experiment 1) and additionally, whether a mindfulness induction, previously documented to improve emotion regulation, would reduce individuals' perception of the degree of valence attributed to the same images (Experiment 2). Contrary to predictions, we report substantial evidence for no effect of prior inhibitory control or a brief mindfulness manipulation on subsequent ratings of emotionally valenced stimuli. Taken together the research indicates that mental exhaustion arising from the use of self-control appears to have no effect on susceptibility to unconscious priming, hypnotic suggestions, and no effect on the perception of emotionally valenced images. However, prior use of inhibitory control does appear to affect the degree of emotional lability experienced following music.

One microfiche in pocket / Bibliography: leaves 329-354 / xxiv, 354 leaves : ill ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, 1986

This thesis has two parts. In the first part, we use the results of new fatigue experiments conducted with variable load levels as well as variable stress ratios to critically assess three (two old and one relatively new) cumulative fatigue damage models. These models are deterministic. Such models are usually tested using multiple blocks of periodic loading with differing amplitudes. However, available data pertains to zero-mean loading, and does not investigate the role of variable stress ratio (Smin/Smax). Here, we present experimental results for variable stress ratios. Two specimen geometries and two materials (Al 2014and Al 2024)are tested. Manson’s double linear damage rule (DLDR)gives the highest accuracy in predicting the experimental outcome, even in the presence of variable stress ratios, whereas predictions of the newer model (“A constructive empirical theory for metal fatigue under block cyclic loading,” Proceedings of the Royal Society A, 464 (2008), 1161-1179) are slightly inferior. The widely used Miner’s rule is least accurate in terms of prediction. The merits and drawbacks of these models, in light of the experimental results, are as follows. The DLDR, though accurate, has minor scientific inconsistencies and no clear generalization. The constructive model has possible generalizability and more appealing scientific consistency, but presently has poorer accuracy. Miner’s rule, least accurate, lies within the constructive approach for special parameter values. The DLDR can guide the new (constructive)approach through new parameter fitting criteria. In the second part of this thesis, we consider the scatter in fatigue life and use the Weibull distribution to describe ‘S-N-P’ curves. We first assume homoscedasticity (load-independent or constant variance) and present a way to draw a p-percentile line on a log-log load-life plot. Then heteroscedasticity (load-dependent variance) in fatigue life is incorporated and a simple statistical model is proposed, to obtain a straight line percentile plot at a pre-specified probability of survival ps. The proposed method is illustrated for Al 2014-T6 and Al 2024-T4 data sets (extracted manually) from MMPDS-01 (a data handbook).

Because of its attractive material properties like high hardness, high toughness, and excellent high temperature strength, materials like silicon nitride are becoming more common for use in high performance applications. However, there have been limited studies of the fatigue behavior of small cracks in silicon nitride and other materials toughened by grain bridging mechanisms. This study explores using micro Raman spectroscopy, fatigue crack growth data and results from static fracture experiments to determine a bridging stress profile for silicon nitride doped with MgO and Y₂O₃ as sintering additives. These bridging stress profiles allow for the creation of a geometry specific fatigue threshold R-curve which can be used to develop a fatigue endurance strength prediction tool to aid in the design of products using the material. Cyclical fatigue experiments conducted on bend beams with induced semi-elliptical surface cracks were conducted to verify the prediction tool. The results show that no bend beams with this crack geometry failed below the predicted endurance level. It is expected that this method can be extended to create fatigue endurance strength predictions for other materials similarly toughened by grain bridging and other mechanisms. / Graduation date: 2013

Syftet med denna systematiska litteraturstudie var att beskriva hur livskvaliteten påverkas hos personer med Multipel Skleros (MS) och vad som kan göras för att öka livskvaliteten. I syftet ingick även att beskriva hur personer med MS upplever fatigue som är ett av huvudsymtomen av sjukdomen samt vad som kan göras för att lindra följderna av fatigue. Artiklarna har sökts i databaserna Elin@Dalarna och Cinahl, tillgängliga via Högskolan Dalarnas proxyserver och granskats med hjälp av en granskningsmall för att säkerställa att de var av en god kvalitet. Sökord som användes var: “multiple sclerosis”, “quality of life”, “nursing” och “fatigue”. Av de artiklar som användes i resultatet var 10 kvantitativa, fyra kvalitativa i en användes båda ansatserna. Resultatet visade att personer med MS generellt sett har en sämre livskvalitet än den övriga befolkningen. Mycket av patienternas livskraft går åt till att bara klara av det dagliga livet. Många personer med MS upplever en stor frustration relaterad till att vilja men inte kunna. Ofta har den försämrade livskvaliteten sin orsak i det sociala livet. Fatigue har ofta en stor påverkan på livet för personer med MS. Det finns en mängd varierande icke farmakologiska behandlingsmetoder som med fördel kan användas för att öka livskvaliteten och minska följderna av fatigue. Exempel på dessa är kylväst, träning och yoga.

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Trait neuroticism, time of day, and day of the week were assessed as predictors of state fatigue. After completing an in-lab questionnaire, 176 participants (N = 176) reported their state subjective fatigue three times a day for 8 days. Trait neuroticism was shown to be a predictor of subjective fatigue states in the morning, early evening, at bedtime, and over the course of the 8-day study period. Additionally, results indicated statistically significant differences in subjective fatigue at different points in the day. A statistically significant Neuroticism X Day of the Week interaction indicated that the neuroticism -fatigue relationship was strongest on Tuesday and weakest on Sunday. The relative contribution of personality, time of day, and day of the week variables to state subjective fatigue are discussed.