Abstract
The effect of annealing (at temperatures below Tg and Tm) on crystal struc ture, crystallinity, and properties of quenched (prepreg) and slow cooled (laminate) J1 (AS4/J1) neat resin (composite) was investigated using various techniques. Because of a complex set of processing dependent crystal structures, WAXD is the most appropriate technique for measuring crystallinity. The effects of annealing on the thermal behavior and on the crystal structure was also studied using DCS and X-ray. The mechanical properties of J1 neat resin and unidirectional graphite fiber AS4/J1 laminates, with and without an nealing at 240°C for 8 hours, have been examined in tension, compression, and three point bend tests. The processing history dependent differences in structure lead to signifi cant differences in mechanical properties in both neat resin and composite. For example, annealing of quenched J1 leads to crystallization and a decrease in elongation whereas an nealing a slow cooled sample at 240°C results in an increase in elongation and toughness. SEM shows different surface morphologies for these samples fractured in tension and three point bend tests. In compression tests, only an in-plane shear flow deformation was seen on the fracture surface of [90]24 AS4/J1 laminate.