Yuichi Nishiyama

Dismantlement behavior and strength of dismantlable adhesive including thermally expansive particles

This paper presents a quite new technique to realize dismantlable joints bonded with adhesive including thermally expansive particles. The thermally expansive particles are a kind of microcapsule consisting of plastic shells filled with liquid hydrocarbon which can expand by adding heat. The volume of the adhesive, including the particles, can also increase due to the expansion of the particles even though the resin of the adhesive has been fully cured, causing the fractures of joints bonded with the adhesive. Since the total expansion of the adhesive depended on the content of the particles, we measured the expansion changing the content of the particles and the temperature. Experiments on joints bonded with the adhesives, which had the different weight fractions of the particles, were carried out in order to immerse them in boiling water or to keep them in hot air. Cracks were generated and then propagated mainly on the interfaces between the adhesive and the adherends of the joints due to internal stress. The joints bonded with the adhesive which included 30 wt% of the particles showed fairly good bond strength and they could be dismantled perfectly in the experiments.

Analysis of gas leakage through C/C composites

Gas leakage through carbon-fiber-reinforced carbon matrix composites (C/Cs) was examined with respect to the application of C/Cs in heat exchangers in an engine system for a future space plane. Because C/Cs have many cracks and pores, gas readily leaks through them. To predict and prevent this gas flow through the C/Cs, leakage rates were measured as a function of pressure, and gas flow paths were identified by microscopic observations of C/Cs. Several analytical models were then used to clarify the principal mechanisms yielding gas-flow resistance. Laminar flow models in tubes and slits were found to give excellent leak-rate predictions compared with experimental results for unidirectionally and three-dimensionally reinforced C/Cs, respectively. A model based on adiabatic expansion and compression, which is used for gas leaks through labyrinth seals, resulted in reasonable agreement with the leak rates through a cross-ply laminated C/C.

Effect of rotational imbalance on fracture rotation speed of carbon-carbon ring

Spin burst tests of carbon-carbon (C/C) rings were carried out to confirm the fracture criterion under high speed rotation as a function of the inner/outer diameter ratio R. The C/C rings were made of a quasi-isotropic lamination type and were confirmed by static tensile tests to have isotropic strength. The burst rotation speeds of the C/C rings were found to be much lower than those expected from stress distributions. A detailed inspection of stress distributions in the C/C rings revealed that a rotational imbalance inherent in C/Cs caused a high average hoop stress and stress concentration around the inner radius. These effects were shown to lower fracture rotation speeds.