Cure path dependency of damage resistance in interlayer toughened composite laminates subjected to quasi-static indentation and low-velocity impact

Cure cycle optimization reduces exotherms, defects and cycle times for thermoset composites, but may change the interlayer microstructure of toughened systems. The question remains, however, how the cure-dependent interlayer microstructure affects laminate mechanical properties. This work studies the effects of cure cycle heating rates on interlayer microstructure and damage resistance of interlayer toughened T800SC/3900-2 laminates, subjected to quasi-static indentation (QSI) and low-velocity impact (LVI). Results show that QSI damage resistance is affected by heating rate and interlaminar microstructure due to the cure-dependent delamination migration. Specifically, a lower heating rate causes separated particles, a thicker interlayer, and more fibre migration into the interlayer, which promotes delamination migration from toughened interlayer to brittle intralayer and consequently weakens the toughening effect. Less delamination migration retains the toughening effect for higher heating rates. In contrast, LVI damage resistance is independent of the cure cycle because delaminations remain in the toughened interlayer for all interlaminar microstructures.