Papers by Author: J.H. Kim

Abstract: Outgassing, the evolution of gas from the material in a vacuum, is not only a source of micro contamination in a semiconductor or the flat display panel production process, but it also a limitation factor in the ultra clean process of nano-technology. The outgassing from the materials of satellites and spacecrafts must be controlled for increased safety and function because space is also a vacuum environment. Several methods are used in outgassing measurement in general, but there is no one method suitable for obtaining all outgassing data. The most suitable method for a particular application must be chosen by the experimenter or user. Three types of outgassing measurement systems were fabricated and characterized, ‘Throughput method,’ ‘Rate of Rise method’ and ‘Mass Loss Measurement method’. The outgassing rates of many kinds of materials were measured and characterized using these systems.

Abstract: The optimal stacking sequence and wall thickness of the composite strut tubes were determined to minimize thermal strains during orbital operation using generic algorithms and finite element analyses. From the results of previous thermal analyses of composite struts with various stacking sequences, the axial deformation is a matter of prime importance. For this reason, the optimization focuses to minimize the axial strains. The balanced and symmetric stacking sequences are used to minimize the radial and the twisting deformations. The genetic algorithm is known to be very effective for the discrete optimization such as stacking sequences of composite materials. As a result, the thermal deformations of the strut with an optimal stacking sequence are almost zero. The optimal strut tube consists of 6 plies and the weight of a composite strut is 22.4% that of aluminum strut. Finite element analyses showed that the optimal design of composite strut tubes withstood combined launch loads without buckling and failure. To validate the analyses, four composite struts were fabricated and their thermal strains were measured under the temperature increase of 100°C. The thermal and vibration experiments showed excellent correlations with analytical results.