Postcuring effects on impact behavior of glass/epoxy composite laminates

Studies had been undertaken on the effects of different postcure schedules on the impact resistance of RT-cured glass/epoxy laminates, subjected to repeated drop tests using an in-house built uninstrumented drop weight impact tester. The impact resistance was assessed in terms of two parameters, viz., the number of drops to failure (N-f) and the delamination area growth (dA). The specimens were postcured at different time-temperature combinations and the impact response was studied at three different incident energy levels (10.6, 12.6, and 14.8J). It was found that, the Nf and dA values increased to a maximum at an optimum postcure schedule of 85 degrees C/4 h. The extent of composite cure for the different postcure schedules was ascertained by measuring the glass transition temperatures (T-g), in order to obtain an appreciation for correlation between the impact resistance and the chemical cure status of the composite. Also, single drop impact studies were made at the 25-J energy level using an instrumented impact tester (DYNATUP 8250) and the aforesaid optimum postcure schedule was reconfirmed.