November 8-12, 2015
Composite materials are increasingly being used in the design of aircraft, train, ship and buildings. They are very often structural parts and they must meet the difficult challenge of having adequate structural fire protection. In fire scenarios of particular relevance according to the targeted applications, suitable strategies to control fire hazards are needed for composite structures. There are three main methods available to design composite structures with improved fire resistance behavior: (i) use “normal” structural materials and add surface protection, (ii) use fire retarded versions of “normal” structural materials, and (iii) use structural materials with inherently good fire retardant properties. The first approach is of interest since it does not modify the intrinsic properties of the structural composites and does not lead to processing problems (e.g. incorporation of fillers in the material). It can be achieved with intumescent coatings: when heating beyond a critical temperature, the intumescent material begins to swell and then to expand forming an insulative coating limiting heat and mass transfers. Intumescence will be used in this work
On the other hand, the evaluation of fire resistance of intumescent coatings protecting structural composite requires large scale equipment. Due to the complexity of fire phenomenon, full-scale tests are still the main and the most credible tool for investigating fire-related issues but they are however very costly, and generally, the cost significantly increases with scale. For those reasons we have developed reliable, repeatable and fast small scale tests including: (i) a furnace delivering temperature/time curves such as ISO 834, UL-1709 and other curves depending on specific fire conditions (curves ‘on demand’), (ii) a jet fuel fire test (according to ISO 2685 or NextGen) devoted to evaluate the fire resistance of components, equipment and structure located in ‘fire zones’ in aircraft (e.g. compartments containing main engines and auxiliary power units) and (iii) a mini Steiner tunnel (according to ASTM E84). It then permits the ‘high throughput’ development of intumescent coatings protecting composites. Examples using the mini Steiner tunnel and the reduced jet fuel fire test will be presented in the talk.
The first example deals with the fire protection carbon fiber reinforced polymer (CFRP) in aircraft structure. Intumescent silicone based-coatings (low and high intumescing coatings) are evaluated on CFRP using a bench mimicking a jet fuel fire occurring at high heat flux (200 kW/m²) (Figure 1). It is shown the development of large intumescence (high intumescing coating) associated with appropriate thermal properties of the coating (heat conductivity measured as low as 0.3 W/m.K) provides efficient protection for the CFRP at the jet fire test. On the other hand, the formation of cohesive ceramic (low intumescing coating) with low heat conductivity (constant heat conductivity as a function of temperature of 0.35 W/m.K) also provides protection but its efficiency is lower than that of intumescent char. It is evidenced that intumescent silicone-based coatings are materials of choice for protecting CFRP in the case of jet fuel fire.
Figure 1 – Jet fuel fire at reduced scale on CFRP protected by an intumescent coating
In the second example, different intumescent coatings protecting polyethylene terephthalate (PET) rigid foams used in roofing structure are evaluated using the mini Steiner tunnel. Results show good correlation between the two scales and the approach developed at the small scale permits the fast screening of intumescent paints to predict their fire behavior at the large scale.
Finally, mechanistic aspects of intumescence based on our small scale tests will be investigated including the chemistry, the physic, the rheology and the modeling of the intumescence
Serge Bourbigot, Fabienne Samyn, and Sophie Duquesne, "Composites on fire at reduced scale: evaluation, characterization and modeling" in "Composites at Lake Louise (CALL 2015)", Dr. Jim Smay, Oklahoma State University, USA Eds, ECI Symposium Series, (2016). http://dc.engconfintl.org/composites_all/66