Laminate processing effect on microvoids and hydraulic fluid absorption of Quartz/BMI laminates

Hurdelbrink K. R., Guloglu G. E., Anderson J. P., Siddique Z., Cengiz Altan M.

20th International Conference on Composite Materials, ICCM 2015, Copenhagen, Denmark, 19 - 24 July 2015, vol.2015-July identifier

  • Publication Type: Conference Paper / Full Text
  • Volume: 2015-July
  • City: Copenhagen
  • Country: Denmark
  • Keywords: Absorption, BMI, Hydraulic fluid, Microvoids, Processing effects
  • Middle East Technical University Affiliated: No


© 2015 International Committee on Composite Materials. All rights reserved.Use of composite materials in complex and robust systems, such as aircraft fuselage and load-bearing structures, is becoming more prevalent as analysis and manufacturing techniques improve. Bismaleimide (BMI) resin with Quartz (AQ581) fiber reinforcement is one such composite material used in products requiring a high glass transition temperature and/or favorable electrical properties such as a low dielectric constant. Laminate fabrication conditions, such as applied cure pressure, can have a significant effect on the liquid absorption characteristics and microvoid formation throughout composite laminates. Long-term composite degradation due to environmental effects, such as absorption of water and other liquid contaminants, must be considered as products with longer service-life become increasingly desirable. Unlike water absorption, the long-term hydraulic fluid absorption by fiber-reinforced laminates has not been studied extensively. Various composite components used in aircrafts are often exposed to different types of hydraulic fluids, which may lead to anomalous absorption behavior over the service life of the composite. Accurate predictive absorption models are important in scheduling necessary repair or replacement during the service life of composites. In this paper, hydraulic fluid absorption characteristics of Quartz/BMI laminates manufactured at different cure pressures are presented. The composite samples are immersed into hydraulic fluid at room temperature, and were not subjected to any prior degradation. To generate process-induced microvoids, all prepregs were conditioned in an environmental chamber at 99% relative humidity at room temperature for a period of 24 hours prior to laminate fabrication. The laminates were then manufactured at cure pressures of 10, 30, 50, and 70 psi via a hot-press. The laminates are shown to have different levels of microvoids ranging from 7.9% to 13.9%, which are also observed to affect the absorption dynamics considerably. The laminates also exhibited clear non-Fickian absorption behavior. A one-dimensional hindered diffusion model (HDM) was successful in predicting the hydraulic fluid absorption behavior. A nearly 50% decrease in maximum mass gain and 8% increase in hindrance coefficient as fabrication pressure increased was observed.