Effects of needle-punched felt structure on mechanicalproperties of carbon/carbon composites

摘要

Carbon fiber reinforced carbon matrix composites (carbon/carbon or C/Crncomposites) are widely used as structural materials in aeronautic and space industriesrndue to their high mechanical properties, higher thermal conductivity and lowerrnthermal expansion coefficient together with good frictional performance in inertrnatmosphere. Unlike other composites, mechanical properties of C/C composites dornnot decrease but even increase at elevated temperature. As a result, studies on theirrnmechanical properties have been carried out in a great deal. This paper deals with therneffects of needle-punched felt structure, including gravity ratio of non-woven cloth tornshort-cut fiber web, carbon fiber types of non-woven cloth and thickness of unit (onernlayer of non-woven cloth and short-cut web is named as a unit), on the C/Crncomposites from pressure gradient CVI. The results are compiled in table1. Resultsrnshow that (a) the compressive strength and modulus decreases but flexural propertiesrnand ILSS increase when gravity ratio of non-woven cloth to short-cut fiber webrnchanges from 7:3 to 6:4. (b) The types of non-woven cloth carbon fiber hardlyrninfluence the compressive properties, but strongly influence the flexural properties.rnThe strength of C/C composites is not linear to the strength of non-woven clothrncarbon fiber because of the important interface between carbon fiber and matrixrncarbon. ? The compressive strength of C/C composites decreases with unitrnthickness, I.e. increases with the unit number per centimeter and a proper thicknessrnrange of unit for higher flexural and interlayer shear strength exists in the presentrnstudy. It exhibits ductile obviously when increasing the unit number per cm of thernneedle-punched felts (fig.1).