Investigation of thermal ageing of advanced CFRP tooling laminate by gas permeability

Exposure of carbon fiber reinforced plastic (CFRP) laminates to elevated temperatures affects the matrix and therefore the composite. A CFRP tool for example, which is usually operated at elevated temperatures, looses its vacuum integrity due ageing effects. Within this work the relation of tooling composite porosity and thermal ageing with subject to the ageing temperature, the laminate thickness and the application of binder within the laminate was observed. The laminate investigated consisted of a quasi isotropic layup and an epoxy matrix with a T_g of 222°C (dynamic mechanical analysis - DMA). Manufactured specimens were loaded by thermal cycles between room temperature and 120°C or 180°C. Methods to investigate the matrix degradation were the determination of the T_g by DMA and of the apparent interlaminar shear strength (ILSS). The results were compared to gas permeability measurements of the aged specimens. Two methods were used to determine the gas permeability of the laminate. First, the pressure drop through the laminate was measured and second the leakage rate was determined by a helium leakage detector. The mechanical test results match with the gas permeability results. Specimen aged at 120°C did not show ageing effects whereas 180°C specimen showed significant degradation.