Influence of out-time on the properties of out-of-autoclave AFP prepregs

In this study, the effect of out-time on the volatile content in the CYCOM® 5320-1 unidirectional prepreg tape is investigated by exposing prepregs to an elevated temperature for periods of 2 hours to 24 hours. In addition, samples based on a [0/±45/90]S stacking sequence were prepared for three exposure durations, these being 2, 24 and 48 hours. The laminates were laid using an in-house fiber placement rig and cured in an oven according to the manufacturer's recommended cure cycle. The glass transition temperature Tg and percentage of cure of the laminates were determined using dynamic mechanical analyzer in a single cantilever mode a differential scanning calorimeter, respectively. The mechanical properties of the laminates were also evaluated following manufacture. The results highlight a linear relationship between volatile uptake and out-time, with a maximum value of 0.6% being associated with an out-time of 24 hours. The exposure duration had a negligible effect on the tensile properties of the manufactured laminates, displaying a variation of ±8% from the mean values. The measured Tg values for the laminates manufactured in this study were similar to those quoted in the manufacturer's data sheet, with there being little change in Tg with prepreg out-time, within the intra-sample variations. The extent of cure of all the laminates manufactured in this work displayed cure values greater than the OEM acceptance criteria of 95%. Micrographs of laminates manufactured from tapes following an out-time of 2 hours show resin-rich areas between the plies, an observation that reduces with increased out-time. The void content in the laminates increased by more than 100% when the out-time was increased from 12 to 24 hours.