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Carbon fibre (CF) and glass fibre (GF) reinforced polymers are used for diverse applications such as electronics/electrical engineering, transportation (railway vehicles, shipping, aviation) and construction. The fire behaviour of composites differs in comparison to polymers. Fibres behave often inert with respect to pyrolysis, but they change the melt flow and dripping behaviour, the heat absorption and transfer, the amount and properties of the fire residue and so on. Flame and fire retardancy concepts are needed not only suitable for the different fire protection goals typical for each application, but also tailored for composites. The field is illuminated by examples taken from different projects carried out in the group of the author in the recent years. The examples target on different applications through achieving V0 in UL 94 testing (reaction to small flame controlling the fire risks in the beginning of a fire), reducing heat release rate and fire load in the cone calorimeter (fire risks under forced flaming combusting controlling the contribution to developing fires) and investigating the fire stability when a severe flame is directly applied (key property in fully developed fires). Approaches to halogen-free flame retardancy in GF reinforced thermoplastics and CF reinforced thermosets are presented as well as building up a bench and intermediate scale testing of composites in fire applying mechanical load and direct flame exposure simultaneously.
The understanding of fire behaviour and flame retardancy mode of actions in composites is a promising basis for target-oriented development. The role of flame inhibition, charring and protective layer formation is discussed in composites. Successful concepts are presented for flame retardancy tailored for different application as well as general guidelines for future development. Different phosphorus flame retardants are proposed to achieve halogen-free flame retardancy in applications demanding limited fire risks with respect to ignition and developing fires. Different protective approaches are sketched for addressing the fire resistance of composite that is the most important fire risk for structural applications.
The application of lightweight materials for tanks for transportation appears promising. Besides saving weight and therefore transportation costs, new complex geometries that depart from common cylindrical shapes of steel tanks can be manufactured. For transportation of dangerous goods, fire and explosion safety must be maintained to prevent accidents with serious consequences. In this work the fire behavior of lightweight tanks made from glass fiber reinforced plastics (GFRP) with complex geometries is investigated. Pretests on intermediate scale GFRP plates are conducted to identify suitable fire protection systems and surface treatments for composite tanks. The fire resistance is shown to be improved by addition of fire protective coatings and integrated layers. Finally, a complex rectangular GFRP tank with a holding capacity of 1100 liters is fire protected with an intumescent fire coating. The tank is filled up to 80 % with water and burned under an engulfing fully developed fire. It was shown that the intumescent layer could expand before the decomposition of the resin occurred. Furthermore, the adhesion between tank surface and coating was maintained. The structure could withstand a fire for more than 20 min.
The fire resistance of load-bearing composite components, e.g. sandwich panels in transportation or stringer reinforced shells used for fuselages, differs in comparison to metal systems. Fibres behave rather inert with respect to pyrolysis reducing burn-through phenomena. The fire stability becomes the main task, because it already breaks down when reaching the softening temperature of the matrix. Fire protection concepts are needed based on efficient thermal insulation and tailored for composite structures.
The fire behaviour of fibre reinforced polymeric composites differs in comparison to polymers. Fibres behave often inert with respect to pyrolysis, they change dripping behaviour, the heat absorption and transfer, the amount and properties of the fire residue and so on. Their fire behaviour becomes somewhat singular. The fire resistance of load-bearing composite components, e.g. sandwich panels for transportation or stringer reinforced shells used for fuselages in aviation, differs in comparison to metal systems. Not burn-through, but the fire stability is typical critical mode of failure. The mechanical failure in fully developed fires can not be explained by the mechanical properties at room temperature, but are controlled by the decomposition and even more important by the softening of the matrix. Fire retardancy concepts are needed based on efficient thermal insulation and tailored for composites. This field is illuminated by examples taken from different projects carried out in the group of the presenting author in the recent years,[1-5] and still running unpublished activities as well. The fire stability is investigated for realistic compression loads, when a severe flame is directly applied (key property in fully developed fires). A bench scale specimen (specimen 150 mm x 150 mm, plates, sandwich, shells) and an intermediate scale (specimen 500 mm x 500 mm, plates, sandwich, shells) fire stability testing was performed. Indeed, e.g. we have investigated the fire stability of stringer reinforced shell components taken out from the fuselage of an aircraft. We applied mechanical load up to 233 kN and 1 MN in the bench-scale and intermediate-scale testing, respectively, and direct flame exposure using burners (180 kW/m2) simultaneously.
The understanding of the fire resistance and fire protection modes of action in composite and composite components is a promising basis for target-oriented development. The role of the fire residue, protective layer formation, and the design of the components is discussed. Successful concepts are presented for increasing the fire resistance of load-bearing composite components as well as general guidelines for future development.
Composites in Fire and Flame
(2022)
Overview over the research results of the BAM in the field fire retardancy of composites. In different applications the flame retardancy of composites targets on different fire protection goals in the fire scenarios ignition, developing fire, and fully developed fire. Efficient solutions are tailored to pass a distinct fire test and to fit to a specific material. Flame inhibition as main flame retardancy mode of action combined with a minor mode of action in the condensed phase is general very efficient approach for composites. Alternatively residue design is demanded to achieve good results with only condensed phase mechanisms. Improving the fire stability asks for protective fire residues.