Void content in carbon/epoxy composites and its effects on flexural properties

A quantitative relationship between void content and flexural properties has been determined for a carbon/epoxy composite material. Differences in void content were achieved using different pressures during the autoclave curing cycle following standard procedures. Areas of different porosity were identified after an ultrasonic double-through-transmission technique. Specimens were then selected and prepared for void content measurement and for three-point flexure test. The testing results were correlated to void volume fraction and ultrasonic absorption coefficient. The study indicates that, in the range from zero to 4 %, each 1 % increase in porosity decreases flexural strength by 7.2% and flexural modulus by 5.5% in this carbon/epoxy composite laminates.