Cure Optimization of 977-2A Carbon/epoxy Composites for Quickstep Processing

  • Laraib Khan

    Student thesis: Phd


    Quickstep is relatively a new technique for manufacturing composites. The cure schedule provided by a prepreg manufacturer is usually designed for autoclave or other traditional processing techniques and the thermosetting resin systems are usually formulated for low ramp rate curing (typically 2-3 K min-1). While in case of Quickstep, ramp rates of up to 15 K min-1 can be achieved, thus changing the chemorheology of the resin system. In this work, an experimental approach is adopted for the optimization of cure cycle for Quickstep of an aerospace grade material (Cycom 977-2A carbon/epoxy prepregs). A step by step account is provided, describing the introduction, balancing and combination of isothermal dwell periods and temperature ramps in order to control resin viscosity and degree of cure. Two important concepts were used to determine the optimum processing parameters for Quickstep processing i.e. proper fibre wetting when the resin was at minimum viscosity and suitable intermediate and upper curing temperature dwell times in order to allow the resin to flow, volatiles to escape and to achieve sufficient degree of cure. All the panels manufactured were quantitatively assessed using ultrasonic C-scan and then fibre content, void content, panel thickness, flexural strength and interlaminar shear strength (ILSS) were assessed. For the ease of comparison, all the properties were compared with those obtained from autoclave and oven cured laminates. It is observed that Quickstep panel properties (QS-60), produced from optimized cure cycle was superior to oven curing and were comparable to autoclave. Mode I and mode II delamination resistance of the QS-60 cured specimens also showed a comparable behaviour as compared to autoclave cured specimens. DSC, DMTA, TGA and FTIR was used to determine the cured characteristics of the QS-60 cured panel and then compared with those cured in autoclave and other Quickstep cure cycles (QSDirect and QSID). The degree and progress of cure was also assessed at different stages of all cure cycles using DSC and FTIR and were compared. It was observed that the reaction path followed by the QS-60 sample was slightly different from autoclave cured samples, however, the final network structure and degree of cure was similar to the autoclave cured samples and comparable to QSdirect and QSID cured sample. QS-60 samples also exhibited the higher Tg as compared to autoclave cured specimens which was attributed to the higher cross-link density achieved through QS-60 cure.Hygrothermal effects on the composite laminates manufactured in an autoclave and Quickstep at 70 ÂșC and 85% RH were also investigated. The results demonstrated that the moisture absorption caused the deleterious effect on the properties and despite of slightly higher moisture absorption, reduction in the flexural, interfacial and glass transition properties of Quickstep panels was comparable to autoclave panel. Thermal stability, reversible and irreversible effects of hygrothermal conditioning using TGA, DMTA and FTIR spectroscopy was also investigated and discussed. The total processing time for autoclave and QS-60 curing was 340 min and 248 min, respectively, thus without compromising panel quality, the overall cure cycle time was reduced by approximately 27% using QS-60 as compared to autoclave.
    Date of Award1 Aug 2010
    Original languageEnglish
    Awarding Institution
    • The University of Manchester
    SupervisorRichard Day (Supervisor)

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