A hermeneutical model of doing research is adopted to investigate the process of coping and self-management in the experience of recovering from Chronic Fatigue Syndrome (CFS). Three research participants who consider themselves as recovering or recovered from CFS were interviewed to obtain data for analysis. The findings are that once the participants cope with the uncertainty about the meaning of the onset of symptoms by defining themselves as ill in somatic terms, the participants use external social and treatment resources to cope with the onset of symptoms and being chronically ill with CFS. As a consequence of feeling stigmatised in relation to social and professional scepticism about initially being ill and subsequently, being chronically ill with CFS, the participants become uncertain about the meaning of having CFS. Coping shifts to using internal resources by adopting self-management practises. In this process, firstly, existing self-management shifts in such a way that the participants view themselves as recovering or recovered from CFS, and secondly, the participants come to the understanding that difficulties with self-management cause and maintain CFS. The findings are discussed to conclude that CFS may be a misdiagnosis of difficulties with self-management. CFS itself may not be an 'objective' disorder, but a constituent of social processes. Becoming diagnosed with CFS arises as a consequence of the search for meaning in relation to the lay and professional assumption that psychological illness does not constitute 'real' illness, operating at both the levels of popular society and the doctor-patient relationship. Difficulties with self-management rather than the diagnosis of CFS provide a more adequate understariding of the participants' illnesses. / KMBT_363 / Adobe Acrobat 9.54 Paper Capture Plug-in

Introdução: Fadiga é uma manifestação clínica importante na artrite reumatoide (AR). Atualmente, a avaliação de fadiga em AR é realizada através de questionários subjetivos, incluindo aspectos emocionais e sociais. No entanto, sabe-se que a fadiga pode estar acentuada no plano periférico e esta abordagem é pouco estudada nestes pacientes. Objetivo: Avaliar a relação entre a percepção de fadiga e fadiga muscular em pacientes com artrite reumatoide. Métodos: Trinta e oito pacientes do sexo feminino com AR foram incluídos. Os pacientes foram estratificados por DAS-28 e por três grupos etários (grupo I: 32-48 anos; grupo II: 49-54 anos de idade, e grupo III: 55-65 anos de idade). A fadiga muscular [avaliado por mudanças na magnitude (root mean square-RMS) e freqüência (média de freqüência-MDF) de ativação muscular durante os 60s do teste de força de quadríceps] e percepção de fadiga (FACIT-F) foram avaliadas. Além disso, dados demográficos [duração idade e doença, calculado pelo tempo decorrido a partir de diagnóstico], hemoglobina (g/ dL), DAS-28, HAQ, qualidade de vida (SF-36) e International Physical Activity Questionnaire (IPAQ, versão longa) foram medidos. A significância foi assumida quando p≤0.05. Resultados: Nenhuma associação foi observada quando os pacientes foram estratificados por DAS-28 e quando os pacientes foram estratificados por idade no grupo III. Moderada correlações estatisticamente significativas entre MDF e FACIT-F e FACIT-TOI (r = 0,6; p = 0,03 e r = 0,5; 0,04, respectivamente) foram encontrados no grupo I. No grupo II foram encontradas moderadas correlações estatisticamente significativas entre FACIT-TOTAL e RMS e MDF (r = 0,6; p = 0,01 e r = -0,5; p = 0,04, respectivamente). Conclusão: Moderada relação entre fadiga muscular e percepção de fadiga sugere que ambas as estratégias de avaliação podem ser complementares e têm um efeito benéfico sobre comorbidades AR. / Introduction: Fatigue is a major clinical manifestation in rheumatoid arthritis (RA). Actually, the assessment of fatigue in RA is realized through to subjective questionnaires, including emotional and socials aspects. However, known to that fatigue may be sharp in peripheral plane and this approach is little studied in these patients. Objective: To assess the relationship between perception of fatigue and muscle fatigue in patients with RA. Methods: Thirty eight female patients with RA were included. Patients were stratified by DAS-28 and by three age groups (group I: 32-48 years old; group II: 49-54 years old; group III: 55-65 years old). Muscle fatigue [assessed by changes in magnitude (i.e. root mean square-RMS) and frequency (i.e. median frequency-MDF) of muscle activation during a 60-s quadriceps strength test] and perception of fatigue (FACIT-F) were assessed. In addition, demographic data [age and disease duration, calculated by elapsed time from diagnostic], hemoglobin (Hb-g/dL), DAS-28, HAQ, quality of life (SF-36) and International Physical Activity Questionnaire (IPAQ, long version) were measured. Significance was assumed when p≤0.05. Results: No association was observed when patients were stratified by DAS-28 and when patients were stratified by age in group III. Moderate statistically significant correlations between MDF and FACIT-F e FACIT-TOI (r=0.6;p=0.03 and r=0.5;0.04, respectively) were found in group I. In group II moderate statistically significant correlations were found between FACIT-TOTAL and RMS and MDF (r=0.6;p=0.01 and r=-0.5;p=0.04, respectively). Conclusion: Moderate relationship between muscle fatigue and perception of fatigue suggests that both evaluation strategies can be complementary and have a beneficial effect on RA comorbidities.

Introdução: Fadiga é uma manifestação clínica importante na artrite reumatoide (AR). Atualmente, a avaliação de fadiga em AR é realizada através de questionários subjetivos, incluindo aspectos emocionais e sociais. No entanto, sabe-se que a fadiga pode estar acentuada no plano periférico e esta abordagem é pouco estudada nestes pacientes. Objetivo: Avaliar a relação entre a percepção de fadiga e fadiga muscular em pacientes com artrite reumatoide. Métodos: Trinta e oito pacientes do sexo feminino com AR foram incluídos. Os pacientes foram estratificados por DAS-28 e por três grupos etários (grupo I: 32-48 anos; grupo II: 49-54 anos de idade, e grupo III: 55-65 anos de idade). A fadiga muscular [avaliado por mudanças na magnitude (root mean square-RMS) e freqüência (média de freqüência-MDF) de ativação muscular durante os 60s do teste de força de quadríceps] e percepção de fadiga (FACIT-F) foram avaliadas. Além disso, dados demográficos [duração idade e doença, calculado pelo tempo decorrido a partir de diagnóstico], hemoglobina (g/ dL), DAS-28, HAQ, qualidade de vida (SF-36) e International Physical Activity Questionnaire (IPAQ, versão longa) foram medidos. A significância foi assumida quando p≤0.05. Resultados: Nenhuma associação foi observada quando os pacientes foram estratificados por DAS-28 e quando os pacientes foram estratificados por idade no grupo III. Moderada correlações estatisticamente significativas entre MDF e FACIT-F e FACIT-TOI (r = 0,6; p = 0,03 e r = 0,5; 0,04, respectivamente) foram encontrados no grupo I. No grupo II foram encontradas moderadas correlações estatisticamente significativas entre FACIT-TOTAL e RMS e MDF (r = 0,6; p = 0,01 e r = -0,5; p = 0,04, respectivamente). Conclusão: Moderada relação entre fadiga muscular e percepção de fadiga sugere que ambas as estratégias de avaliação podem ser complementares e têm um efeito benéfico sobre comorbidades AR. / Introduction: Fatigue is a major clinical manifestation in rheumatoid arthritis (RA). Actually, the assessment of fatigue in RA is realized through to subjective questionnaires, including emotional and socials aspects. However, known to that fatigue may be sharp in peripheral plane and this approach is little studied in these patients. Objective: To assess the relationship between perception of fatigue and muscle fatigue in patients with RA. Methods: Thirty eight female patients with RA were included. Patients were stratified by DAS-28 and by three age groups (group I: 32-48 years old; group II: 49-54 years old; group III: 55-65 years old). Muscle fatigue [assessed by changes in magnitude (i.e. root mean square-RMS) and frequency (i.e. median frequency-MDF) of muscle activation during a 60-s quadriceps strength test] and perception of fatigue (FACIT-F) were assessed. In addition, demographic data [age and disease duration, calculated by elapsed time from diagnostic], hemoglobin (Hb-g/dL), DAS-28, HAQ, quality of life (SF-36) and International Physical Activity Questionnaire (IPAQ, long version) were measured. Significance was assumed when p≤0.05. Results: No association was observed when patients were stratified by DAS-28 and when patients were stratified by age in group III. Moderate statistically significant correlations between MDF and FACIT-F e FACIT-TOI (r=0.6;p=0.03 and r=0.5;0.04, respectively) were found in group I. In group II moderate statistically significant correlations were found between FACIT-TOTAL and RMS and MDF (r=0.6;p=0.01 and r=-0.5;p=0.04, respectively). Conclusion: Moderate relationship between muscle fatigue and perception of fatigue suggests that both evaluation strategies can be complementary and have a beneficial effect on RA comorbidities.

Introdução: Fadiga é uma manifestação clínica importante na artrite reumatoide (AR). Atualmente, a avaliação de fadiga em AR é realizada através de questionários subjetivos, incluindo aspectos emocionais e sociais. No entanto, sabe-se que a fadiga pode estar acentuada no plano periférico e esta abordagem é pouco estudada nestes pacientes. Objetivo: Avaliar a relação entre a percepção de fadiga e fadiga muscular em pacientes com artrite reumatoide. Métodos: Trinta e oito pacientes do sexo feminino com AR foram incluídos. Os pacientes foram estratificados por DAS-28 e por três grupos etários (grupo I: 32-48 anos; grupo II: 49-54 anos de idade, e grupo III: 55-65 anos de idade). A fadiga muscular [avaliado por mudanças na magnitude (root mean square-RMS) e freqüência (média de freqüência-MDF) de ativação muscular durante os 60s do teste de força de quadríceps] e percepção de fadiga (FACIT-F) foram avaliadas. Além disso, dados demográficos [duração idade e doença, calculado pelo tempo decorrido a partir de diagnóstico], hemoglobina (g/ dL), DAS-28, HAQ, qualidade de vida (SF-36) e International Physical Activity Questionnaire (IPAQ, versão longa) foram medidos. A significância foi assumida quando p≤0.05. Resultados: Nenhuma associação foi observada quando os pacientes foram estratificados por DAS-28 e quando os pacientes foram estratificados por idade no grupo III. Moderada correlações estatisticamente significativas entre MDF e FACIT-F e FACIT-TOI (r = 0,6; p = 0,03 e r = 0,5; 0,04, respectivamente) foram encontrados no grupo I. No grupo II foram encontradas moderadas correlações estatisticamente significativas entre FACIT-TOTAL e RMS e MDF (r = 0,6; p = 0,01 e r = -0,5; p = 0,04, respectivamente). Conclusão: Moderada relação entre fadiga muscular e percepção de fadiga sugere que ambas as estratégias de avaliação podem ser complementares e têm um efeito benéfico sobre comorbidades AR. / Introduction: Fatigue is a major clinical manifestation in rheumatoid arthritis (RA). Actually, the assessment of fatigue in RA is realized through to subjective questionnaires, including emotional and socials aspects. However, known to that fatigue may be sharp in peripheral plane and this approach is little studied in these patients. Objective: To assess the relationship between perception of fatigue and muscle fatigue in patients with RA. Methods: Thirty eight female patients with RA were included. Patients were stratified by DAS-28 and by three age groups (group I: 32-48 years old; group II: 49-54 years old; group III: 55-65 years old). Muscle fatigue [assessed by changes in magnitude (i.e. root mean square-RMS) and frequency (i.e. median frequency-MDF) of muscle activation during a 60-s quadriceps strength test] and perception of fatigue (FACIT-F) were assessed. In addition, demographic data [age and disease duration, calculated by elapsed time from diagnostic], hemoglobin (Hb-g/dL), DAS-28, HAQ, quality of life (SF-36) and International Physical Activity Questionnaire (IPAQ, long version) were measured. Significance was assumed when p≤0.05. Results: No association was observed when patients were stratified by DAS-28 and when patients were stratified by age in group III. Moderate statistically significant correlations between MDF and FACIT-F e FACIT-TOI (r=0.6;p=0.03 and r=0.5;0.04, respectively) were found in group I. In group II moderate statistically significant correlations were found between FACIT-TOTAL and RMS and MDF (r=0.6;p=0.01 and r=-0.5;p=0.04, respectively). Conclusion: Moderate relationship between muscle fatigue and perception of fatigue suggests that both evaluation strategies can be complementary and have a beneficial effect on RA comorbidities.

Fatigue is defined as an exercise-induced decrease in maximal voluntary force produced by a muscle. Fatigue may arise from central and/or peripheral mechanisms. Supraspinal fatigue (a component of central fatigue) is defined as a suboptimal output from the motor cortex and measured using transcranial magnetic stimulation (TMS). Reductions in O2 supply (hypoxia) exacerbate fatigue and as the severity of hypoxia increases, central mechanisms of fatigue are thought to contribute more to exercise intolerance. In study 1, the feasibility of TMS to measure cortical voluntary activation and supraspinal fatigue of human knee-extensors was determined. TMS produced reliable measurements of cortical voluntary activation within- and between-days, and enabled the assessment of supraspinal fatigue. In study 2, the mechanisms of fatigue during single-limb exercise in normoxia (arterial O2 saturation [SaO2] ~98%), and mild to severe hypoxia (SaO2 93-80%) were determined. Hypoxia did not alter neuromuscular function or cortical voluntary activation of the knee-extensors at rest, despite large reductions in cerebral oxygenation. Maximal force declined by ~30% after single-limb exercise in all conditions, despite reduced exercise time in severe-hypoxia compared to normoxia (15.9 ± 5.4 vs. 24.7 ± 5.5 min; p < 0.05). Peripheral mechanisms of fatigue contributed more to the reduction in force generating capacity of the knee-extensors following single-limb exercise in normoxia and mild- to moderate-hypoxia, whereas supraspinal fatigue played a greater role in severe-hypoxia. In study 3, the effect of constant-load cycling exercise to the limit of tolerance in hypoxia (SaO2 ~80%) and normoxia was investigated. Time to the limit of tolerance was significantly shorter in hypoxia compared to normoxia (3.6 ± 1.3 vs. 8.1 ± 2.9 min; p < 0.001). The reductions in maximal voluntary force and knee-extensor twitch force at task-failure were not different in hypoxia compared to normoxia. However, the level of supraspinal fatigue was exacerbated in hypoxia, and occurred in parallel with reductions in cerebral oxygenation and O2 delivery. Supraspinal fatigue contributes to the decrease in whole-body exercise tolerance in hypoxia, presumably as a consequence of inadequate O2 delivery to the brain.

The main purpose of this research project was to determine the fatigue-life behaviour of AISI 1008 sheet steel which has been mechanically formed to a radius of curvature of 120mm and then to correlate the fatigue-life behaviour to that of the parent or “as manufactured” material. During the forming process it was felt important to induce plastic strain through stretch-bending by clamping the sides of a plate sample’s (width) edges in the bending fixture before being bent by a single acting mechanical press. It was determined through actual testing that there was a decrease in fatigue-life when the mechanical formed data was compared to fatigue data of the parent material. Standard fatigue mathematical models were used to relate the actual fatigue data. Due to the material being cold formed to a radius of curvature of 120mm, residual stresses induced during the forming process played an essential role during the fatigue-life prediction calculations. The maximum relieved stress in the parent material was compressive in nature having a magnitude of 11percent of the “as manufactured” yield strength (265 MPa). For the mechanical formed material compressive residual stresses were measured on the outer surface while tensile stresses were measured on the inner surface. The difference between actual number of cycles to failure to that calculated using the standard mathematical models for the parent material, ranged between 48 percent and 18 percent and for the mechanical formed samples between 35 percent and 1percent, depending on the strain amplitude used. An important aspect of this study was to determine the criteria required for mathematical modelling of the parent material as testing occurred between the limit of proportionality and yield point. Although this aspect requires further investigation the mathematical results obtained during this study were considered to be acceptable.

Cette thèse s'inscrit dans un programme de développement technologique de la Société LEONI. Ce programme de recherche a pour principal objectif de disposer, à l'issue des trois années de l'étude, d'un panel de connaissances scientifiques le plus pertinent possible sur la durabilité des alliages d'aluminium dans des environnements caractéristiques d'un faisceau électrique automobile. Il s'agit, à terme, d'intégrer, à l'échelle industrielle, l'aluminium ou l'un de ses alliages dans les câblages électriques automobiles. Après une première étape de sélection des matériaux, l'alliage retenu est un alliage d'aluminium 6101. La fabrication des faisceaux électriques automobiles nécessite l'utilisation de brins de petits diamètres qui sont obtenus, à partir d'une ébauche, par un procédé de mise en forme associant plusieurs étapes de tréfilage et de revenu. Chacune de ces étapes conditionne les propriétés de l'alliage. Les travaux réalisés dans le cadre de cette thèse ont eu pour objectif d'analyser et de quantifier l'influence des différentes étapes de ce procédé de mise en forme sur la durabilité de l'alliage 6101. Compte tenu de l'environnement en service des faisceaux électriques, deux types de sollicitation ont été considérés ; ces sollicitations sont associées à un endommagement en corrosion d'une part et à un endommagement en fatigue-corrosion d'autre part. La première partie de ces travaux est donc consacrée à une étude du comportement en corrosion en milieu contenant des ions chlorures de l'alliage d'aluminium AA 6101 à l'état métallurgique T4, correspondant à l'état microstructural du matériau d'ébauche. L'influence des traitements thermomécaniques liés au procédé de mise en forme des fils fins sur la microstructure, les propriétés mécaniques et le comportement en corrosion de l'alliage AA 6101 fait l'objet de la seconde partie des travaux. Enfin, l'influence de contraintes mécaniques cycliques sur le comportement en corrosion de l'alliage AA 6101 en milieu NaCl 0,5M a été étudiée. L'ensemble de ces résultats met en évidence un couplage environnementmicrostructure-état de contraintes avec un fort impact des traitements thermo-mécaniques sur les microstructures et donc sur les propriétés mécaniques et le comportement en corrosion du matériau / This work is in the framework of a technological development program with LEONI. The aim of this program research is to bring technical skills and scientific knowledge, the most pertinent as possible on the durability of aluminum alloys in automotive harness environment. The purpose is to integrate aluminum alloys in automotive wiring systems. After a first step of materials selection, the AA 6101 aluminum alloy has been selected. Automotive wiring harnesses need small diameters of strands which are obtained by a forming process combining several cold-drawing steps and aging heat treatments. Each step of this forming process influences the alloy properties. The aim of this work is to analyze and quantify the influence of each step of the forming process on the durability of AA 6101 aluminum alloy. Considering the automotive harness environment, two kinds of damages have been studied: corrosion damage in one hand and fatigue-corrosion damages in the other hand. The first part of this work was dedicated to the study of the corrosion behavior of AA 6101 aluminum alloy at T4 metallurgical state in chloride media. The influence of thermo-mechanical treatments, due to the process forming of the strands on the microstructure, the mechanical properties and the corrosion behavior of the AA 6101 has been studied in the second part. Finally, the influence of cyclic mechanical stresses on the corrosion behavior, i.e. fatigue-corrosion phenomena, of the AA 6101 in 0.5M NaCl has been considered. The whole results highlight a coupling between environment-microstructure-stress states with a severe influence of the thermo-mechanical treatments on the microstructures, the mechanical properties and on the corrosion behavior

Ce travail a consisté premièrement en une étude en cross over comparant l’effet d’une sieste versus une période de repos sur une mesure électrophysiologique de récupération motrice post-exercice chez des patients fatigués atteints de sclérose en plaques (SEP) (n=12) et des témoins sains (n=12). Cette mesure correspondait à l'amplitude des potentiels moteurs évoqués par la stimulation magnétique corticale et enregistrés au niveau de la main effectuant l'exercice. Cette étude a montré que la fonction restauratrice du sommeil sur la récupération de la dépression des potentiels évoqués moteurs post-exercice était altérée chez les patients atteints de SEP et fatigués comparativement à la population témoin. Deuxièmement, une étude comparative de la puissance spectrale de la bande de fréquence delta et sigma dans les différents stades de sommeil puis de la pente des ondes lentes du sommeil lent profond a été effectuée à partir de données polysomnographiques dans une série de patients atteints de SEP et fatigués (n=15) comparés à des sujets sains (n=15). L’hypothèse posée était que la perte de l’effet restaurateur du sommeil sur les performances motrices dans la SEP pouvait être le reflet d’un dysfonctionnement de la synchronisation de certains réseaux neuronaux. Nos résultats ne montrent pas d’altération de la pente des ondes lentes chez les patients atteints de SEP comparativement aux sujets sains, ce qui invalide notre hypothèse. Cependant, une diminution de la puissance spectrale dans les bandes de fréquences sigma et delta a été retrouvée chez les patients atteints de SEP comparativement à la population témoin. Ce résultat pourrait être expliqué par des différences concernant les microéveils corticaux, les mouvements périodiques de jambes éveillants ou le sex-ratio entre les deux groupes. L'implication d'une altération des connexions thalamo-corticales par atteinte myélinique dans la perte de la fonction restauratrice du sommeil reste tout de même une hypothèse à explorer dans le cadre de la SEP. / This work consisted first in a crossover study comparing the effect of a nap versus a rest on an electrophysiological measure of post-exercise motor recovery in fatigued patients with multiple sclerosis (MS) (n = 12) and healthy controls (n = 12). This measure corresponded to the amplitude of motor potentials evoked by magnetic stimulation of the cortex, recorded at the hand performing the exercise. This study showed that the restorative function of sleep on the recovery of post-exercise motor evoked potential depression was impaired in fatigued MS patients compared to controls. Second, a comparative study of the spectral power density in the sigma and delta bands at different stages of sleep and of the slope of slow wave during deep sleep was conducted from polysomnographic data in a series of fatigued MS patients (n = 15) compared to healthy subjects (n = 15). The assumption was that the loss of the restorative effect of sleep on motor performance in MS could be due to a dysfunction of synchronization in some neural networks. Our results show no impairment of slow waves slope in patients with MS compared to healthy subjects, which invalidates our hypothesis. However, a decrease in the spectral power density in the sigma and delta bands was found in patients with MS as compared to controls. This result could be explained by differences in micro-arousals, periodic movements of legs or sex-ratio between the two groups. The involvement of an alteration in thalamocortical connections due to myelin damage in the loss of the restorative function of sleep still remains a hypothesis to be explored as part of MS.

This dissertation involves the experimental investigation of commercially pure titanium (CP Ti) which was subjected to laser forming and mechanical forming processes. Commercially pure titanium grade 2 was formed to a radius of curvature of approximately 120 mm using three forming procedures, i.e. i) laser forming; ii) mechanical forming (stretched forming) and iii) a combined forming process (laser-mechanical forming). Fatigue testing revealed, for all the forming processes, that samples produced by laser forming performed the best at high load settings. However, mechanically formed specimens performed the best at low load settings, whereas the laser-mechanical process resulted in midway performance between laser and mechanical processing. Considering microstructure vs fatigue; impact vs fatigue; and residual stress vs fatigue; at high load settings it is evident that the microstructure is the dominant contributor to crack initiation and growth. Crack morphology of fatigue samples revealed that secondary cracks (parallel to main crack front) followed the grain boundaries of the Widmanstätten microstructure, whereas irregular secondary cracks grew parallel and through the twinning planes and along the grain boundaries of the equiaxed microstructure. Laser forming resulted in microstructural changes from equiaxed grains to a Widmanstätten structure due to fast cooling rates. Excessive twinning is developed within the equiaxed microstructure after the mechanical forming procedure. This is due to cold working / strain hardening. The combined process shows a combination of equiaxed grains and Widmanstätten microstructure. Residual stress relieved for all forming processes revealed an increase in the magnitude of the residual stress compared to the parent plate and that the maximum values were obtained at the inner radius of curvature (i.e. 118.4 mm). Laser forming revealed the highest values in residual stress whereas the other two processes i.e. mechanical and laser-mechanical forming exhibited an increase midway between the parent plate and laser forming. The second most influential factor with regards to fatigue was the magnitude of the residual stress, especially at medium to low load settings. When considering theoretical models to predict fatigue life it was found that the Goodman model showed the closest relation to the actual fatigue data when considering the entire theoretical curve. Vickers microhardness profiling was applied to the thickness of the samples for the parent plate and all forming processes. No significant hardening occurred due to the forming processes and differences in hardness were considered negligible. Charpy impact testing revealed that the laser formed specimens exhibited the most brittle behaviour when compared to the parent plate results. Mechanical formed specimens showed a slight increase in brittleness compared to parent plate whereas the combined process yielded results midway between the laser and mechanically formed specimens. Mathematical equations are formulated and presented for predicting the fatigue life of CP Ti grade 2 for the parent plate and the three forming processes. This study proved that the laser forming process can be successfully used as a production stage in the forming of CP Ti grade 2.

An investigation of the effect of R-ratio on the mode II fatigue delamination of AS4/3501-6 carbon/epoxy composites has been undertaken. Experiments have been performed on end notched cantilever beam specimens over a wide range of R-ratios (-l ≤R ≤0.50). The measured delamination growth rate data have been correlated with the mode II values of strain energy release rate range ∆G[formula omitted]), maximum strain energy release rate (G[formula omitted]) and stress intensity factor range (∆K[formula omitted]). The growth rate is dependent on the R-ratio over the range tested. For a constant level of ∆G[formula omitted], the crack growth rate decreases with increasing R-ratio. A similar trend is observed when the data is plotted as a function of G[formula omitted]. The effect of plotting the growth rate as a function of ∆K[formula omitted] is to produce an R-ratio dependence opposite to that obtained by either the ∆G[formula omitted] or G[formula omitted] approach. For a constant level of ∆K[formula omitted], the crack growth rate increases with increasing R-ratio. Master equations which completely characterize the fatigue behaviour as a function of ∆G[formula omitted] and ∆K[formula omitted] have been derived, based on the observation that the growth rate law exponent, n and constant, A are unique functions of R-ratio. Values for n are surprisingly large and increase with increasing R-ratio whereas values for A decrease with increasing R-ratio. The effect of time-at-load has been considered in an attempt to explain the existence of the R-ratio dependence of the growth rate. The correct trend can be established for the exponent, n but not for the constant, A. Friction between the crack faces, particularly at higher R-ratios, is proposed as a possible explanation for the observed anomaly. Further evidence of a frictional mechanism operating at higher R-ratios has been discovered through a postmortem fracture surface examination. Additional fractographic observations are presented over the entire range of R-ratios tested. In regions subjected to negative R-ratio cycling, there is no evidence of the characteristic mode II hackle features. Instead, loose rounded particles of matrix material are found. An extensive amount of hackling is observed in regions subjected to low positive R-ratio cycles. The extent of hackle damage visibly decreases in areas where higher levels of R-ratio are imposed. A correlation between the general fracture surface morphology and the fatigue data provides support for the hypothesis that energy for delamination is always available in sufficient quantity, and that growth is dependent on the stresses ahead of the crack tip being sufficiently high. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate