The influence of temperature and moisture on the mode I fracture toughness and associated fracture morphology of a highly toughened aerospace CFRP

This paper addresses the characterisation of the mode I interlaminar fracture toughness of a carbon fibre/epoxy composite material, toughened with thermoplastic particles in the ply interlayers. The characterisation is undertaken at -55 degrees C, 19 degrees C, and 90 degrees C, on both dry and fully moisture saturated coupons. Fractographic observations of the delamination surfaces allows identification of the failure mechanisms. The mode I propagation fracture toughness tested at wet/90 degrees C exhibits a 176% increase compared to the dry/19 degrees C specimens, due to enhanced plastic deformation of the interlayers and more prominent fibre bridging. Moisture-saturated coupons tested at -55 degrees C suffered a 57% reduction of mode I fracture toughness compared to those under dry/19 degrees C conditions. This is due to the dis-bond and consequent plucking of the thermoplastic particles from the surrounding matrix. This observation points to the fact that wet/cold conditions may represent the worst-case scenario for the interlaminar fracture performance of composite systems toughened with thermoplastic interleaves.

Automated summary

The study found that the mode I propagation fracture toughness tested at wet/90 degrees C showed a 176% increase compared to the dry/19 degrees C specimens, due to enhanced plastic deformation of the interlayers and more prominent fibre bridging. However, moisture-saturated coupons tested at -55 degrees C suffered a 57% reduction of mode I fracture toughness compared to those under dry/19 degrees C conditions, which is attributed to the dis-bond and consequent plucking of the thermoplastic particles from the surrounding matrix. This suggests that wet/cold conditions may represent the worst-case scenario for the interlaminar fracture performance of composite systems toughened with thermoplastic interleaves.