The purposes of this study were to investigate the effect that strength level had upon fatigue and recuperation under the two conditions of five- and thirty-second interval duration periods. Another purpose was to compare the results of this study to similar studies using male subjects in order to determine if women's response patterns to tests of strength were similar to those of men.

Le but de cette étude est la prédiction de la durée de vie à l'initiation de la fissure d'un contact acier/aluminium sous la sollicitation de fretting fatigue. La prédiction des durées de vie a été déterminée à l'amorçage des fissures en fonction des différents chargements appliqués. Un dispositif expérimental adapté sur un banc d'essai multiaxial de fatigue a été mis au point. Des essais ont été réalisés sur un alliage d’aluminium de la série 6082T6. Les résultats obtenus montrent un abattement de la durée de vie par rapport à la fatigue classique. La modélisation par éléments finis a été menée en utilisant un code de calcul Abaqus. Les champs de contraintes et de déformations identifiés ont été utilisés sur différents critères de fatigue multiaxiale basés sur les plans critiques. Les résultats de la prédiction donne une sous estimation de la durée de vie en fretting fatigue. Ceci est dû aux forts gradients présents dans la zone de contact. La prédiction a été améliorée par couplage d’une méthode de champs moyens avec les critères de fatigue multiaxiale. Les estimations obtenues présentent une bonne corrélation avec les résultats expérimentaux. Néanmoins, la taille de la zone d'élaboration optimale semble dépendre du critère de fatigue multiaxiale utilisé et des conditions de chargement appliquées. Cette zone ne semble pas être liée directement avec la microstructure pour le matériau étudié.Dans une structure les sollicitations sont variables. La démarche ci-dessus a été couplée avec deux lois d'endommagement: loi de Miner et loi dite de la contrainte endommagée pour la prédiction avec des chargements par blocs. Les prédictions obtenues sont satisfaisantes. / The purpose of this study is to predict fretting fatigue crack nucleation of a mono contact steel/aluminum at different applied loads.An experimental device was first designed and adapted on a multiaxial fatigue apparatus. Tests were conducted aluminum alloy at constant amplitude loading under both different load levels and load ratios. As expected, the fretting fatigue life was found lower compared to uniaxial fatigue under the same loading conditions. Finite element analysis was conducted using \textit{Abaqus} software. The computed stress and strain fields were used to estimate the parameters of different multiaxial fatigue criteria based on the critical plane approach. When using stress and strain values corresponding to the material point exhibiting the maximum value of the considered parameter, we have found that, whatever the multiaxial fatigue parameter, conservative fatigue life estimates due to the severe gradients in the contact zone. An averaging method of the mechanical quantities over a given reference volume was then used to attenuate these gradients effects. The estimates show a good correlation with experimental results. However, the size of the reference volume depends on both the multiaxial fatigue criteria and on loading conditions applied. So that it could not be directly linked to the grain size for the material studied. Finally, we made an attempt to extend these criteria and the developed method to variable loadings. Fretting fatigue tests using two and four blocks loadings were performed and the previous criteria were coupled with two damage laws. The estimates we have obtained seems very promising.

No description available.

Approved for public release, distribution unlimited. / This study compares an experimental watchstanding schedule derived at Naval Submarine Medical Research Laboratory (NSMRL) with the schedule currently used onboard the submarine USS HENRY M. JACKSON (SSBN 730 GOLD). It analyzes subjective and objective data to determine if the new schedule is compatible in an operational submarine environment. This study reviews sleep and fatigue literature to emphasize important concepts needed to make schedule comparisons. Results from this study indicate a need exists among the U.S. submarine force to employ an operational schedule which provides more sleep and which is in better alignment with human circadian rhythms, thus improving cognitive effectiveness. One of the experimental schedules tested in this study yielded results similar to those of the existing submarine watchstanding schedule. This experimental schedule employed a validated model of human performance and fatigue to assess individual cognitive effectiveness. However, the results also indicate that the existing schedule is better suited in its accommodation of operational scheduling constraints which, in turn, allow watchstanders to receive more sleep. Recommendations address the need for the U.S. submarine force to continue to pursue a watchstanding schedule that provides better sleep while still accommodating operational constraints. Recommendations also address improvements in experiment implementation which can be integrated into future studies. / Lieutenant, United States Navy

A dissertation submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science in Engineering. Johannesburg 1988 / Fatigue crack closure characteristics were studied in a 70i7 aluminium alloy in the as received (AR) and heat treated (HT) conditions with the view of establishing the general closure trends and how well the modified closure parameter AKeff (- K^ax ' K0_) was capable of characterising fatigue crack growth. The results of this work indicated that a significant amount of strain intensification occurred below K0p which implied that AKe££ generally underestimated the stress intensity range experienced at the crack tip during cyclic loading. The major objective of this dissertation was to determin' whether a relationship exists between the distance over which closure develops from zero to a steady state jlcsure value, and the distance over which short crack growth behaviour occurs. Two techniques were used to eliminate closure for a fatigue crack in a compact temion specimen. Closure development was then measured as a function crack length and a steady state closure value was approached tier about 0.19 mm in the AR material and 0.?8 mm in the HT material irrespective of AK. This distance compared well with that distance over which short cracks exhibited "anomalous" behaviour. This implies that anomalous short ctack behaviour is dependent on the distance over which closure develops in this alloy, although microstructural influences may play a rola.

Master of Arts - Psychology / A traumatic event is characterised by a situation that involves the actual or threatened death or injury to one’s self or others (Hesse, 2002). Figley (1999) described traumatic stress from another perspective in that individuals exposed to a traumatised person, may experience emotional upset and may become a victim, indirectly of the traumatic event. Secondary Traumatic Stress (STS) emerges suddenly and without warning. The sufferer of STS often experience feelings of confusion and helplessness. Compassion fatigue, an equivalent to STS first made appearance in studies of job burnout in the helping professions to describe a decline in compassionate feelings toward patients or clients in need. Compassion fatigue has since been widely used external to the occupational context, thus in the wider social community (Kinnick, Krugman & Cameron, 1996). In literature, a clear frame is presented by the Constructivist Self Development Theory and focuses on the multifaceted interaction between the ind ividual and the environment. According to this theory individuals construct their own realities. The self is the seat of the individual’s identity and inner life, which encompasses four interrelated aspects: selfesteem, ego resources, psychological needs and cognitive schemas. Traumatic experiences are encoded in the verbal and imagery systems of the memory. Adaptation to trauma reflects an interaction between life experiences and the self (McCann & Pearlman, 1990). Neurotic anxiety, Type A syndrome, locus of control, flexibility, and introversion as the five personality traits, guide an individual’s responses to stress (Cherniss, 1980). Not only personality traits, but also career goals and previous experiences may influence an individual’s suscep tibility to stress. In contrast, coping strategies are influenced by social support such as family involvement and friends, and the load of stress on the individual (Harel, B. Kahana and E. Kahana, 1993). Freud suggested that fixation on trauma is biolo gically based and posttraumatic stress disorder is associated with complex abnormalities in several biological systems (Van der Kolk and Saporta, 1993). When considering the complexity of our biological system combined with the complexity of the human psyche, trauma counselling is energy consuming on both the victim and the counsellor. An additional theory explored was the Psychoanalytical theory which focuses on the intrapsychic processes and infantile conflict (Brett, 1993). Three basic assumptions are the core of the psychoanalytic theory, according to Meyer, Moore and Viljoen (1997). These are: psychosocial conflict, biological and psychological determinants, and mechanistic assumption based on natural sciences and indicates that an individual functions like a mechanism with energy and the functions thereof. Considering the difference between compassion fatigue and burnout, numerous researchers indicate the importance of distinguishing between these concepts. Figley (1999), indicates burnout as a result of emotional exhaustion and specifies that it also has a gradual emergence, in contrast to compassion fatigue which emerge suddenly and is associated with feelings of hopelessness and confusion, although the recovery rate is faster than that of burnout. According to Maslach (1982), burnout is: a syndrome of emotional exhaustion, depersonalisation and reduced personal accomplishments. Burnout may also be a logic outcome of lower levels of autonomy, control over practice, collaborative working relationships, and organisational trust as indicated by Spence Laschinger, Shamian and Thomson (2001. According to Hesse (2002), organisations may introduce interventions to assist employees in combating symptoms of compassion fatigue and burnout, or the foreseeing event of these symptoms occurring. These are: reduction of the number of caseloads each trauma counsellor are responsible for and provision of supervision and group support programmes to assist employe es in rendering these effects. Furthermore, organisations should ensure adequate benefits, staff development opportunities, regular leave, informed consent as a standard organisational policy to inform new counsellors of the risks involved in trauma counselling and expressive staff meetings An unfavourable effect may be caused by suffering therapists to their organisations in that the quality and effectiveness of the organisation's work may be compromised. Therapists who do not address compassion fatigue and burnout are likely to experience more disruption of their empathic abilities, resulting in frequent incomplete therapies (Waldrop, 2003). The objective of this research is to determine the organisational responses towards compassion fatigue and burnout in trauma counsellors. A comparison between organisational responses across multiple organisations model will be made to explore the effects of the various responses. Furthermore, the study will investigate the influences of organisational responses on compassion fatigue and burnout considering the influences individual differences of the trauma counsellors may have. The need to establish the organisational responses towards compassion fatigue and burnout in any given organisation may assist researchers, employees and organisations alike to proactively intervene in such incidence. Not only is it ethical to intervene but potential problems concerning employees may also become legality. The Occupational Health and Safety Act is a legal guide provided for employees and employers alike. Concerning the research design, a quantitative approach was employed to reach the research objectives. The target population for this study included counsellors working with trauma survivors. No volunteer counsellors were used for the reason that different responses are associated with volunteer counsellors beyond the scope of this study. The sample comprised of 25 (n) trauma counsellors in total. The total sample of 25 counsellors participating in the study, 19 were female and five (5)were male, with one response missing. The method of data collection was by means of structured questionnaires, more specifically, compassion fatigue and burnout was measured through the Professional Quality of Life: Compassion Satisfaction and Fatigue Subscales – Revision III (ProQol – RIII) and the Organisational questionnaire which was constructed by the researcher. The reliability scores of the ProQol – RIII obtained by the researcher indicated the first subscale, compassion satisfaction .92, the burnout subscale with an alpha of .62 and lastly compassion fatigue subscale with an alpha of .66. All statistical analysis was obtained with the assistance of the SAS Programme (SAS Institute, 2000). Descriptive statistics were used to analyse the data of the different organisations (Kerlinger & Lee, 2000). Content analysis was used to describe each organisation and organisational responses to compassion fatigue and burnout. Profiles for each organisation were developed ant in that the relationship between organisational responses and possible compassion fatigue was examined. The most prominent results were the following: Unanimous responses to no provision of primary interventions such as change of line of authority (70%), restructuring of organisational units in order to prevent monotony (76%), establishment of reward systems (81%), and information regarding issues concerning the Occupational Health and Safety Act (81%). Agreement among respondents that organisations do not providing time management training (86%), conflict management training (86%), focus groups or support groups (80), and health promotional activities such as weight-watchers (75%) were reached. Unanimous agreement was also observed regarding organisations not providing in-house counselling or referrals were. All organisations have average to low compassion satisfaction scores and all organisations tend to have average to high compassion fatigue with burnout being lower for all organisations except Organisation 1 with a tendency of higher burnout. Due to not finding phenomenal significant relationship between the organisation profiles when addressing the predictive power of organisational responses, the predictive power when individual differences are accounted for, became irrelevant. Janik (1995), stipulates that employees in every domain are at risk of developing compassion fatigue. These include correctional officers, counsellors, psychologists, social workers, emergency response personnel, and medical staff. We as employees and employers must unite to assist each other in combating these phenomena.

A survey has been made of the developments of welding processes and the literature concerned with the fatigue resistance of butt welded joints. Evident from the literature survey was the fact that a mass of experimental data was available on the fatigue properties of welds yet many fatigue failures were still being reported. It appears essential therefore that the design data derived from experimental results should be presented in a meaningful way to aid the safe design of welded connections. Fatigue tests were conducted on specimens cut from 1/2 in. thick plate of medium carbon steel, over a range of alternating and mean stress levels. The welds were produced using manual metal arc, gas metal arc and electron beam welding processes and manufactured in industry by accepted production methods. A non destructive examination together with static tests were carried out on both the parent material and the welded joints. The results obtained have enabled a comparison to be made between the data obtained from static, dynamic and non destructive tests. The analysis shows some evidence of correlation between the information derived from the static and non destructive tests with that of fatigue performance. A method of analysing fatigue data, based on the method of least squares, has been developed. This provides good fits to data when used in conjunction with modified versions by Goodman and Gerber of the basic Jefferson empirical fatigue equation. The fatigue curves generated by this method can be described by two equation constants which can subsequently be used to generate a family of fatigue curves over a range of mean loads. The method of analysis is also capable of calculating confidence limits on experimental data for both stress and fatigue life for the predicted fatigue curve.

"Residual stresses are a common and often undesired result of material processing, introduced through non-linear deformation and/or phase transformation of material under mechanical or thermo-mechanical loading. These macro stresses alter mechanical properties and the intrinsic fatigue crack growth characteristics of the material. Residual stress artifacts can introduce inconsistencies and significant errors when the true material behavior is needed for material development and optimization and for structural component design. The effects of quenching residual stresses on fatigue crack propagation behavior of various materials were investigated. In parallel, residual stresses similar in magnitude and distribution with the quenching residual stresses were generated using mechanical processes to decouple the effects of residual stresses from microstructural effects. Mechanical residual stress distributions predicted by 3D elastic-plastic finite element analysis showed good agreement with the stresses measured on fatigue crack growth testing specimens using fracture mechanics approaches. Crack propagation characteristics in fields with low and high residual stresses were studied using optical and scanning electron microscopy, and the effects of residual stress on crack path behavior were assessed. An original residual stress analytical correction to fatigue crack growth data was developed, compared to existing corrective methodologies, and validated using residual stress free data. Overall, the work provides tools to understand, control, and correct the effects of processing residual stresses on fatigue crack growth for accurate fatigue critical design and life predictions."

La nitruration gazeuse est un traitement thermochimique permettant une meilleure résistance à la fatigue grâce à l’apport de propriétés mécaniques importantes telles que l’augmentation de la dureté et les contraintes résiduelles de compressions. Cette étude est réalisée sur un acier 33CrMoV12-9 utilisé dans l’industrie aéronautique. Un modèle complet adapté à cette nuance permet de quantifier les profils de contraintes résiduelles et de dureté en fonction des paramètres de nitruration. La prise en compte de l’apport de ces propriétés mécaniques est possible grâce à l’utilisation de critère de fatigue de type Crossland. Ce type de critère est intégré dans une méthodologie, afin de calculer la limite en fatigue dans une couche nitrurée et prédire la résistance de la pièce, ainsi que la potentielle zone d’initiation de rupture en fonction d’un chargement, d’une durée de vie et d’une probabilité à rupture donnés. L’utilisation combinée du modèle de calcul des propriétés mécaniques (dureté et contraintes résiduelles) et de la prédiction de l’initiation de rupture dans un matériau nitruré, rend possible une méthode inverse permettant de calculer les paramètres de nitruration adaptés à un chargement subi. Cette approche se justifie dans le cas de nitruration gazeuse, car il a été démontré lors de cette étude, que ce traitement reste robuste face au chargement subi par la pièce. / Gaseous nitriding is a thermochemical treatment that improves fatigue strength by providing important mechanical properties such as increased hardness and residual compressive stresses. This study is carried out on a 33CrMoV12-9 steel used in the aeronautical industry. A complete model adapted to this grade allows to quantify the residual stress and hardness profiles as a function of the nitriding parameters. Taking into account the contribution of these mechanical properties is possible thanks to the use of fatigue criterion such as Crossland. This type of criterion is integrated in a methodology in order to calculate the fatigue limit in a nitrided layer and to predict the resistance of the workpiece, as well as the potential initiation zone of rupture according to a load, a lifetime And a given break probability. The combination of the model for the calculation of mechanical properties (hardness and residual stresses) and the prediction of the initiation of rupture in a nitrided material, makes possible an inverse method allowing to calculate the nitriding parameters adapted to a load suffered. This approach is justified in the case of gaseous nitriding because it has been demonstrated in this study that this treatment remains robust against the loading undergone by the workpiece.

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