The changes in flexural properties and microstructures of carbon fiber bismaleimide composite after exposure to a high temperature

Recent increase in the use of carbon fiber reinforced polymer composites, especially for high temperature applications, has created new challenges to predict their service life. This paper examines the changes in weight loss and flexural properties along with the changes in microstructures of unidirectional carbon fiber reinforced bismaleimide with [0(16)] and [90(16)] specimens, after exposure to 260 degrees C for 3000 h in air. The percentage of fiber end area exposed to air in a specimen end section significantly influences the extent of these changes. The [90(16)] specimens have an order of magnitude higher fiber open ends than the [0(16)] specimens, and their weight loss rate and loss in flexural modulus and strength are significantly higher than that of the [0(16)] specimens. In three point bending, interlaminar shear leads to delamination preceding the final failure in compressive mode. A viscoelastic cohesive layer model has been implemented to simulate interlaminar delamination. Viscoelastic regularization of the constitutive equations of the cohesive layer used in this model not only mitigates numerical instability, but also predicts load-deflection behavior beyond peak failure load. The model is in a good agreement with experimental results and has been able to simulate the delamination failure successfully. (C) 2013 Elsevier Ltd. All rights reserved.