Abstract not available

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No description available.

An understanding of the problems associated with a very large light weight structure orbiting in space is of utmost importance at present. A knowledge of how the structure behaves under the influence of external disturbances in space should be available for any design and deployment of a structure in space. The life, efficiency, and function of the space structure are dependent on this knowledge. A mathematical formulation has been developed for an axially flexible structure executing a planar motion in a general orbit in space in order to determine dynamic and thermal effects in the structure due to various disturbances in a space environment. The characteristic dimension of the structure is very large (of the order of a few kilometers). We have studied the influences of the differential gravitational forces, the radiation heating, and the radiation pressure forces. Effects of these factors have been studied on the structure's axial deformation, its attitude motion and its orbit simultaneously. Results are obtained for various initial conditions and physical parameter values. It is observed that the differential gravitational forces do not have any appreciable effects on the structure's axial length and its attitude motion. Thermal effects are significant in producing appreciable structural deformation, and they also affect the attitude motion of the structure considerably. The radiation pressure forces are very significant in changing attitude motion of the space structure, but it causes negligible effects in producing longitudinal deformation of the structure. All of the above factors have insignificant effects on the orbit of the structure chosen in this study. Of all the three external disturbances, the radiation pressure forces are found to be strongest in affecting the orbit of the structure.

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No description available.

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No description available.

As current aerospace materials are subjected in service to increasingly onerous conditions of stress and temperature, the hazard of fatigue failure becomes more acute. Engineers utilise the methodology of fracture mechanics to estimate fatigue crack growth rates but fatigue crack initiation, which involves the interplay of many microprocesses, is only investigated empirically. The aim of this study was to investigate the fatigue damage accumulation mechanisms in the titanium alloy IMI 834 in order to develop a fundamental understanding of the controlling physical processes and the micromechanisms which occur at the dislocation level. Load controlled four point bend test specimens of IMI 834 were cyclically fatigued to failure with an R ratio of 0.1 over a range of maximum stress levels and the fatigue and fracture surfaces were examined by optical and scanning electron microscopy. The examination of cross-sectional foils prepared from the fatigue surface enabled the fatigue damage to be examined in the T.E.N. as a function of orientation and depth below the specimen surface. The distribution, orientation and type of slip bands were identified in the primary-a and the transformed-fJ grains, and their interaction with secondary phases, precipitates and grain boundaries was determined. The results show that fatigue damage accumulation in INI 834 occurs primarily on basal slip bands in the primary-a phase and on basal and prismatic slip bands in the transformed-fJ phase. The segregation of a-stabilising elements to the primary-a phase during alloy processing allows the formation of an ordered phase which increases the propensity for planar slip on the basal plane. A mechanism for fatigue crack initiation along this plane is proposed. In addition, the occurrence and identification of an interface phase is discussed in the light of current theories regarding this phase.