Development of Non-contact NDE Method for Autoclave Cure Monitoring of Carbon-phenolic composites by On-line Gas Chromatography Technique

摘要

During re-entry phase of the long range missiles, they experience severe aerodynamic friction and high surface temperatures. In this context, carbon-epoxy shell is used as internal structural layer and carbon-phenolic shell is used as external layer for production of re-entry vehicle structure. Autoclave curing is used for production of external thermal shells of Re-entry vehicle structures of the missiles. Autoclave curing of phenolic composites involves a complex regime of time - temperature -pressure cycle where selection of pressure application point is the most important parameter, decides the quality of the component. Early pressure application with respect the gelation produces resin starved component, which degrade the thermal performance of the component whereas late pressure application produces more porosity in the component due to trapping of volatiles generated due to curing chemical reaction. Production of high resin content and minimum void distribution is most essential and which is achieved by analyzing the volatiles evolved during the process. During curing process, m-phenol and water are the one of the indicators and the concentrations are determined by suitable detectors as a function of temperature of the component. Based on the diminishing trend of the curves the gelation region for pressure application was determined. A new contact NDE method for cure monitoring of carbon-phenolic composites was developed right from development of concept, realization, development of proto type system for assessing the advancement of curing reaction and for determination of gelation region for pressure application. The system contains gas sample injection port, gas-chromatograph, detector unit, software for signal analysis. The equipment and experimental details were presented in the paper.