Cure temperature variation and hygrothermal effects on an out-of-autoclave polymer composite

Abstract

The effects of cure temperature variation and hygrothermal conditioning on thermal, physical, and mechanical properties of an out-of-autoclave prepreg were investigated and correlated. To study the effects of cure temperature variation, intermediate-cure temperature, second ramp rate, and post-cure temperature were varied from a recommended two-stage cure cycle. The effects of adverse environmental conditions on the cure temperature variation were studied by conditioning the samples in boiling water and a conditioning chamber. The material’s cure state was monitored using a Different Scanning Calorimeter (DSC), Encapsulated Sample Rheometer (ESR), and Dynamic Mechanical Analyzer (DMA). An ultrasonic C-scan and void content tests were performed to map the void distribution in the cured laminates. The mechanical properties were obtained using Short-Beam Shear (SBS) and Combined Loading Compression (CLC) test methods. A further investigation on failure modes was also done on mechanical tested coupons using the photoanalysis method. The results from the ESR and DSC showed that complex viscosity and degree of cure were changed during cure while the final degree of cure, glass transition temperature, and SBS strength did not show significant difference for intermediate-cure temperature ranging from 99oC to 110oC and second-ramp up rate variation ranging from 1.1oC/min to 2.2oC/min. For post-cure temperature variation from 99oC to 143oC, good correlations were obtained between the material’s cure temperatures, state of cure, and mechanical properties for dry room temperature and hot/wet conditions. The study showed that material’s cure state should be used to define and monitor the cure quality rather than using a time-temperature specification.