Resin injection of bisphenol E cyanate ester, a low viscosity resin that cures into a high temperature thermoset polymer, is investigated as a reliable repair method to restore strength and stiffness in delaminated carbon fiber/bismaleimide composites used in aircraft panels. The influence of temperature on the viscosity of the uncured resin was measured to optimize the injection conditions for high resin infiltration into the delaminations. The repair efficiency of the resin was evaluated by varying the panel thickness and the method by which the delamination damage was created in the composite specimens. Ultrasonic scanning (C-scan), flash thermography images, and cross-section analysis of repaired panels revealed excellent resin infiltration into the damaged region. Evaluation of mechanical repair efficiency using both bending stiffness and in-plain compressive strength of the composite panels as the repair metrics showed values exceeding 100%.
Cyanate esters are a group of resins with exceptional thermal and mechanical properties and are often blended with lower cost epoxy resins. These blends are often brittle, and a toughening method, such as the addition of soft segments, is necessary. Poly(ethylene glycol) diglycidyl ether, or PEGDE, was added to bisphenol E cyanate ester as a toughening agent. PEGDE was added at loadings of 0-30 wt %, and rheological and mechanical properties were analyzed after curing. As PEGDE loading was increased, the gel point increased accordingly while the activation energy of gelation decreased, indicating PEGDE accelerated the gelation process. Dynamic mechanical analysis results indicated a decrease in glass transition temperature as the PEGDE loading increased. Three-point bending tests yielded similar toughness to the neat BECy at low PEGDE loadings, with a dramatic increase at loadings of 25 and 30 wt % PEGDE.
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