The purpose of this study has been to make a biomechanical analysis of the dislocate as performed on the still rings. All testing was done in the gymnasium at the University of British Columbia with each of the five subjects taking three trials. Cable tension was monitored with strain gauges attached in series withthe ring cable. Each trial was filmed, and film and force records were synchronized with a flash gun which caused a timing mark to be placed on the chart recorder paper. When the subject felt he was ready the first of three trials was executed. There was a two minute rest between each trial to negate any effect of fatigue. After the completion of the third and final trial the subject was asked which trial he thought was the best of the three. The film record of the dislocate was later shown to a panel of experts who rated each dislocate. The rating by the panel of experts allowed each dislocate to be ranked in order of excellence. This rank order was the chosen criterion against which the biomechanical measurements were evaluated for the aim in coaching gymnastics is eventually to satisfy the subjective impression of the judges. The information recorded by the film was refined with the use of the Vanguard Motion Analyzer. Obtained were the following measures. a) position of the rings b) body position c) displacement of noted body landmarks The following conclusions were drawn from this study: 1. The patterns of force and body actions are similar for all subjects. Given these similarities it is difficult to identify measures which correlate highly with good performance. 2. The angular velocity of the movement of the legs at the second and third peaks of force is not well correlated with either experts' ranking (r = 0.18) or maximal force (r = 0.25). 3. The following are poor predictors of performance in the dislocate: a) Total range of angular displacement of the ring cable. b) Time (frames) between the second and third peaks of force. c) Angular displacement of the ring cable during the second and third peaks of force. d) Kipping angle. e) Amount of preparatory vertical drop of hips in the kipping phase. 4. Better performers are those who maximize the upward force during the kipping phase by accentuating the rise of the hips over that of the ankles. Consequently it is suggested that those teaching this activity concern themselves with methods of maximizing the upward thrust of the hips in the kipping phase. It is felt that this phase is the foundation block upon which the dislocate is built. / Education, Faculty of / Curriculum and Pedagogy (EDCP), Department of / Graduate

Work-hardened metals typically possess large numbers of dislocations in complex three-dimensional configurations about which little is known theoretically. Here these large numbers of dislocations are accounted for by means of a dislocation density tensor, which is obtained by applying an averaging process to families of discrete dislocations. Some simple continuous distributions are examined and an analogy is drawn with solenoids in electromagnetism before the question of the equilibrium of dislocation configurations is studied. It is then proved that the only finite, simply-connected distribution of dislocations in equilibrium in the absence of applied stresses are ones in which all components of stress vanish everywhere. Some examples of these zero stress everywhere (ZSE) distributions are then given, and the concept of 'plastic distortion' is used to facilitate their interpretation as rotations of the crystal lattice. Plastic distortion can also be understood as a distribution of infinitesimal dislocation loops ('Kroupa loops'), and this idea is used in Chapter 4 to investigate the dislocation distributions which correspond to elastic inclusions. The evolution, under an applied stress, of some simple ZSEs is analysed, and the idea of 'polarisation' is introduced, again in analogy with electromagnetism. Finally, a mechanism is conjectured for the onset of plastic flow.

An investigation as to the characteristics of flow and fracture for alpha-uranium were carried out over the temperature range -196°C to 270°C. The parameters relevant to grain size and strain rate were investigated. It was established that the flow stress and the fracture stress in the semi-brittle region vary linearly with the grain size parameter (1/D½). Evidence suggests that the sensitivity of flow stress to grain size is directly related to the importance of glide dislocation action as the deformation mode. Strain rate change irreversibility was found to exist at low strains for all temperatures investigated. This evidence, correlated with the effect of grain size, indicates that massive structural changes occur in the early stages of flow. This agrees with electron transmission microscopy results as established by other workers. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

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Thèse de doctorat : Mécanique des matérieaux : Metz : 2007. / Thèse soutenue sur ensemble de travaux. Bibliogr. f. 146-149.

Growing economical and ecological requirements have driven the automotive industry towards lowering fuel consumption by reducing vehicle weight and in the meantime maintaining safety standards. This pushes the development of advanced light weight alloys. As a promising candidate for automotive applications, the twinning induced plasticity (TWIP) steels have received tremendous attention due to their superior mechanical properties, which combines high ultimate tensile strength and ductility simultaneously. However, their plasticity mechanism and recovery behavior are still not completely understood. In the first part of this investigation, a modified physical-based model is developed based on the recent observations of strong influence of grain orientation and Bauschinger effect. The model describes well the serrated plastic flow of Fe-22Mn-0.6C TWIP steel under quasi-static tensile loading at ambient temperature. The discrete twinning is considered responsible for the serration phenomenon in Fe-22Mn-0.6C TWIP steel. The model also provides a new approach to estimate the volume fraction of deformation twins. In the second part of this investigation, the recovery of pre-strained Fe-22Mn-0.6C TWIP steel is studied. A model describes the evolution of yield stress during annealing is proposed, which indicates that the recovery treatment does not remove deformation twins induced by cold rolling but decreases dislocation density in matrix and removes the dislocations piled up against twin and grain boundaries. The recovery activation energy rec Q is derived from experimental results. The value Qrec = 1.73 eV = 167 kJ/mol implies that the diffusion from dislocations cores governs the recovery of investigated TWIP steel. / published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

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