Publications

Cure cycle development and qualification for thick-section composites

Warnock, Corinne M.; Briggs, Timothy B.

The kinetics of thermoset resin cure are multifaceted, with flow and wet-out being dependent on viscosity, devolatilization being a function of partial pressures, and crosslinking being dependent on temperature. A unique cure recipe must be developed to address and control each factor simultaneously. In the case of thick-section composites, an uncontrolled exotherm could cause the panel to cure from the inside out, causing severe process-induced residual stresses. To identify and control the peak heat generation from the exothermic crosslinking reaction, differential scanning calorimetry (DSC) was conducted for different candidate cure schedules. Resin rheology data and dynamic mechanical analysis (DMA) results were used to confirm a viable resin viscosity profile for each cure schedule. These experiments showed which isothermal holds and ramp rates best served to decrease the exothermic peak as well as when to apply pressure and vent the applied vacuum. From these data, a cure cycle was developed and applied to the material system. During cure, embedded thermocouples were used to monitor heat generation and drive cure temperature ramps and dwells. Ultrasonic testing and visual inspection by microscopy revealed good compaction and < 1 % porosity for two different composite panels with the same resin system. DSC of post-cured samples of each panel indicated a high degree of cure throughout the thickness of the panels, further qualifying the proven-in process.