Principle Investigator(s) (PIs): Matthew Priddy, Thomas Lacy, Jr.
Collaborators: Charles Pittman, Jr., Santanu Kundu, Aj Madabhushi, Hasnaa Ouidadi, Hajar Rigui, Aniket Mote, Dounia Boushab
Collaborating Universities: Mississippi State University
Funding Agencies: Federal Aviation Administration (FAA)
Program Monitor: Dave Stanley
Summary
Due to their high strength-to-weight and stiffness-to-weight ratios, excellent corrosion resistance, and ease of manufacture/repair, fiber-reinforced composite materials are increasingly used in a wide range of applications including aircraft structures. However, due to their extensive use, composite materials are exposed to extreme mechanical and/or thermal stresses which can severely degrade aircraft flight safety, damage tolerance, and structural integrity. For example, aircraft fires are the fourth highest contributor to commercial aviation fatalities. In-flight aircraft fires may result in severe degradations in composite material performance and reductions in overall flight safety. Fire effects on fiber-reinforced composite materials include matrix and organic fibers decomposition/pyrolysis, porosity formation due to volatile outgassing from matrix decomposition, delamination, matrix cracking, char formation, etc. In addition, post-crash fire can drastically degrade the mechanical properties of composite materials and alter the features and morphology of their failed surfaces in ways that mask relevant aspects of the structural damage morphology and other evidence necessary to identify the underlying failure mechanisms, leading to catastrophic structural failures. Therefore, the analysis of the response of fiber-reinforced composite materials to fire and the understanding of their fire resistance is considered a key technical challenge to ensure flight safety.
For this purpose, the Federal Aviation Administration (FAA) has funded our research group to perform a “Post-Crash Fire Forensic Analysis on Aerospace Composites.” As part of this project, a series of experimental tests will be performed to investigate the effect of fire on carbon/epoxy composite laminates failed in Mode I Mode II or mixed-mode failure. Fire tests on the failed specimens will be performed using both Bunsen burner and cone-calorimeter. Furthermore, an investigation of various physical and chemical techniques will be used as a tentative for char and other fire by-products removal to identify post-fire failure surface characteristics. Finally, multi-scale models will be developed to predict the progressive degradation of the thermal and mechanical properties of carbon/epoxy composites as a function of increasing temperature, heat flux, and exposure time.
Figure 1: SEM micrographs of the flat surface after 30s of fire exposure.
(SEM performed at Mississippi State University)
Figure 2: SEM micrographs of the edge surface after 30s of fire exposure.
(SEM performed at Mississippi State University)
Figure 3: SEM micrographs of the progressive thermal damage on a single carbon-fiber due to a controlled open-flame at a standoff distance of 0.5 in
(SEM performed at Mississippi State University)