Characterization of the effects of multiple cure cycles on a carbon fiber epoxy composite

Abstract

The effects of a secondary cure cycle on the mechanical and physical properties of a carbon fiber epoxy composite were evaluated. The secondary cure cycle represents one of several possible scenarios such as secondary bonding operation, repairs using a higher temperature adhesive or any other elevated temperature exposure. The subject material was Cytec's HMF7740/T650-35-3K-PW-195-HM. This material consisted of HMF7740 epoxy impregnated into plain weave T-650 carbon fiber. Two sets of test laminates were prepared using a 250°F cure cycle. The first set was cured using the designated cure cycle. The second set was also cured using the same cure cycle but was then exposed to the same cure cycle again. Using the AGATE-based methodology contained in report DOT/FAA/AR-03/19 [1], mechanical and physical test data was generated for comparison. Tests were conducted to evaluate the effects on 90° Tensile, 90° Compressive, In-Plane Shear, Interlaminar Shear, Open-Hole Compression, Resin, Fiber and Void Contents and the Glass Transition Temperature. While slight differences were detected in some of the tests results, overall, there was minimal difference between the two sets of laminates.