Characterization of the Flammability and Thermal Decomposition Properties of Aircraft Skin Composite Materials and Combustible Surrogates

 Currently, the aircraft industry is shifting toward the use of new aircraft skin materials. In place of aluminum, aircraft are now being constructed from composite materials, which typically include combustible components. The objective of this test series was to quantify the small-scale burn characteristics of two new aircraft skin composite materials and a candidate wood surrogate. If testing was successful, a wood surrogate could be used as a readily available, cost-effective in future large-scale flammability and suppression tests. A series of small-scale fire tests and analytical test methods were conducted to characterize the flammability and thermal decomposition properties of the materials. These tests were designed to develop a data set that could be used to validate intermediate scale tests and as input in the development of flame spread and thermal decomposition models for these materials. The composite materials evaluated were a carbon fiber-reinforced polymer (CFRP) and a glass laminate aluminum reinforced epoxy (GLARE), and the wood surrogate evaluated was an oriented strand board (OSB). The small-scale fire tests conducted in this research included cone calorimetry testing, lateral ignition and flame spread testing, and thermal decomposition testing. The analytical work conducted included thermogravimetric analysis, differential scanning calorimetry, and pyrolysis gas chromatograph/mass spectroscopy. The materials’ flammability and thermal decomposition properties were derived from these tests. Tests suggest the average heat capacity during decomposition and the average thermal conductivities of the two materials is similar. This indicates the OSB is a reasonable surrogate for the CFRP over the course of the decomposition process when the heat capacity and thermal conductivity parameters strongly influence the results. The overall average apparent heat capacity is comparable, which is consistent with the heat capacity results of the thermal decomposition apparatus. This suggests the OSB is a reasonable overall surrogate material for the CFRP when the heat capacity is a significant parameter, but there may be significant differences in thermal absorption rates on smaller time scales.

DOT/FAA/TC-14/1

Authors: Christopher Mealy, Haavard Boehmer, Joseph L. Scheffey, and Gerard G. Back