| 초록 |
Fiber-reinforced polymer composites (FRPC) have been taken into consideration as a promising material in cryogenic applications due to their exceptional mechanical properties even under extreme low-temperature conditions. One of critical factors to be considered for the usage in the severe environment is the discrepancy of the thermal contraction between reinforcing fibers and matrix resins. The difference of the contractions which directly correspond to the coefficient of thermal expansion (CTE) can lead to the interfacial failure resulting in deterioration of mechanical properties of the composites, in particular, reinforced with continuous fibers. Another important point is the improvement of low temperature strength or toughness of the matrix resins itself. In this work, dimethylpolysiloxane liquid was blended with diglycidyl ether of bisphenol-A epoxy resin including anhydride curing agent to improve the tensile strength of the epoxy resin at 77K without any increase in its coefficient of thermal expansion (CTE). A bifunctional polymer, silicone-modified epoxy resin (SME), was also added to the mixture as a compatibilizer. The results of UV transmittance for the blend resin showed that the incorporation of the SME could stabilize effectively spherical domains of the siloxane liquid which was immiscible with the epoxy matrix. The tensile strengths of the blend resins at both room temperature and 77K were measured and SEM analysis for the fractured cross sections was carried out to verify the toughening behavior of the liquid droplets. The results indicated that even small amount of addition of the siloxane liquid (0.05 phr) coupled with SME (20 phr) could enhance the tensile strength at 77K by 77.6% compared to that of the neat epoxy resin. This improvement is attributed to the fact that the solid and stable droplets can disperse the localized stress and interrupt the crack propagation by cavitation mechanism followed by multiple generation of numerous micro-deformation. From the CTE measurement, the siloxane liquid has no influence on the thermal contraction behavior of the blend resin. |
