ROLE OF INTERFACIAL GASEOUS HEAT-TRANSFER IN THE TRANSVERSE THERMAL-CONDUCTIVITY OF A UNIAXIAL CARBON-FIBER-REINFORCED ALUMINOBOROSILICATE GLASS

The transverse thermal conductivity of an aluminoborosilicate glass un iaxially reinforced with carbon fibers was found to be lower under nea r-vacuum than in nitrogen, whereas no such difference was found for th e longitudinal thermal conductivity. This effect was attributed to the existence of an interfacial gap resulting from the thermal expansion mismatch between the matrix and fibers. The presence of this gap permi ts the gaseous environment access to the fiber-matrix interface and th ereby contributes to the interfacial heat transfer. Its presence does not affect the longitudinal thermal conductivity, however, because the gap is aligned parallel to the fibers and, therefore, the direction o f heat flow. Analysis of the experimental data indicates that, in nitr ogen at atmospheric pressure, the gaseous conductance constitutes abou t one-third of the total interfacial conductance.