YunHo Kim

Ring burst test of filament wound composites for environmental resistance

The use of filament-wound composites can be advantageous, especially for designing parts of aircraft structures, because of superior mechanical properties of the composites. On the other hand, various experiments are necessary for studying the environmental resistance of composites rather than that of conventional metals. A hoop ring burst test would be a convenient and reliable method for the evaluation of the environmental resistance of a composite pressure vessel. In this research, a method with 24 split disks was developed for estimating the impact and thermal shock resistance of a carbon-fiber-reinforced composite pressure vessel using hoop ring burst specimens subjected to high-speed impact. Impact tests were conducted with a 12.7-mm diameter ceramic ball at a speed of approximately 40–110 m/s. After the impact test, three cycles of thermal shock were conducted on the half of the specimens. C-scan analysis was conducted to determine whether there was any internal damage after the tests. Finally, the hoop ring burst test using 24 split pressure disks was conducted for modified ring specimens. Through this procedure, the proposed method was successfully verified with a number of tests.

High Velocity Impact Characteristics of Shear Thickening Fluid Impregnated Kevlar Fabric

The development of high performance fabrics have advanced body armor technology and improved ballistic performance while maintaining flexibility. Utilization of the shear thickening phenomenon exhibited by Shear Thickening Fluids (STF) has allowed further enhancement without hindering flexibility of the fabric through a process of impregnation. The effect of STF impregnation on the ballistic performance of fabrics has been studied for impact velocities below 700 m/s. Studies of STF-impregnated fabrics for high velocity impacts, which would provide a transition to significantly higher velocity ranges, are lacking. This study aims to investigate the effect of STF impregnation on the high velocity impact characteristics of Kevlar fabric by effectively dispersing silica nanoparticles in a suspension, impregnating Kevlar fabrics, and performing high velocity impact experiments with projectile velocities in the range of 1 km/s to compare the post impact characteristics between neat Kevlar and impregnated Kevlar fabrics. 100 nm diameter silica nanoparticles were dispersed using a homogenizer and sonicator in a solution of polyethylene glycol (PEG) and diluted with methanol for effective impregnation to Kevlar fabric, and the methanol was evaporated in a heat oven. High velocity impact of STF-impregnated Kevlar fabric revealed differences in the post impact rear formation compared to neat Kevlar.