EFFECT OF DELAMINATION ON THE TRANSVERSE THERMAL-CONDUCTIVITY OF A SIC-FIBER-REINFORCED SIC-MATRIX COMPOSITE

The effect of delamination on the transverse thermal conductivity of a biaxial multiweave SiC-fiber-reinforced chemical-vapor-infiltrated-ma trix composite was studied. The delamination process, induced by compr essive loading, consisted of enlarging and widening pre-existing inter ply cavities in the as-received composite. Ultrasonic scanning suggest ed that the delamination process resulted in mechanical debonding betw een the plies. At room temperature, the delamination reduced the trans verse thermal conductivity by a factor of similar to 5, As a result of gaseous conduction in the interply cavities and/or delamination, the thermal conductivity was higher in air/nitrogen at atmospheric pressur e than under vacuum, a difference that was especially pronounced in th e delaminated sample. The thermal conductivity of the as-received and delaminated samples exhibited a negative and positive temperature depe ndence, respectively, which resulted in almost-equal values at tempera tures >1000 degrees C, Data analysis showed that the thermal conductiv ity of the delaminated composite was almost independent of the thermal conductivity of the plies themselves; instead, the thermal conductivi ty of the composite was controlled primarily by conduction across the delaminations at areas of direct contact, conduction through the gaseo us phase within the delaminations, and radiation across the delaminati ons.