Mechanical properties evolution during cure for out-of-autoclave carbon-epoxy prepregs
Extent of cure and rheological properties were obtained for out-of autoclave materials, Cycom 5320-8HS and Cycom 5320-PW, for the manufacturer recommended cure cycle using Differential Scanning Calorimeter (DSC) and Encapsulated Sample Rheometer (ESR), respectively. Rheological properties from ESR were further used in designing the cure cycles to study the evolution of mechanical properties. Five panels were cured at different cure stages using the designed cure cycles and coupons were tested for short beam shear and combined loading compression properties at different cure stages. To correlate the mechanical properties with its respective glass transition temperature, Dynamic Mechanical Analyzer (DMA) was used to obtain the glass transition temperature for the coupons obtained from the respective panels. Statistical results showed significant difference in short beam shear and combined loading compression properties up to vitrification, however, no significant difference was observed on these mechanical properties after vitrification. The observed linear trend between degree of cure (DOC) and glass transition temperature (Tg) was validated using Dibenedetto relation. Linearly increasing trend between degree of cure (DOC) and glass transition temperature (Tg) for different cure states suggests that both DOC and Tg can be used interchangeably to define the state of material. A good correlation was observed between material cure state and the mechanical properties. A mathematical model was also proposed to determine the short beam shear and combined loading compression properties based on material cure state.