Effect of vacuum thermal cyclic exposures on the carbon/carbon composites

• The effect of vacuum thermal cycling on C/C composites was showed systematically.
• An abnormal phenomenon of thermal expansion of C/C composites under cryogenic temperature was discussed by Raman spectrum.
• The flexural strength showed a recovery tendency (28.84%) after 100 thermal cycles.
• An interfacial damage model based on microscopic observation was proposed.

The study aims to investigate the effects of vacuum thermal cycling on carbon/carbon (C/C) composites used in aerospace under simulated low earth orbit (LEO) environmental conditions. The C/C composites were tested at the temperature range from −120 °C to 120 °C for 100 cycles under the high-vacuum state of 1.3x10−3Pa, the composites were characterized through the assessment of the thermal physical and mechanical property changes. It follows from the experiment that the cyclic thermal stress derived from thermal cycling could influence the stability of C/C composites which result in an abnormal phenomenon of thermal expansion of C/C composites under cryogenic temperature. The flexural strength initially decreases from 105.51 MPa to 74.83 MPa with the thermal cycles increasing to 30, then increases to 96.41 MPa after 100 thermal cycles, showing a recovery tendency (28.84%) of flexural strength compared with 30 thermal cycles and maintains the initial flexural strength of 91.39%.The implications of these processes based on the relation between coefficients of C/C composites between vacuum thermal cycling were discussed and an interfacial damage model based on microscopic observation was proposed.