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SUMMARY The influence of the orientation of carbon fibres on the reaction‐to‐fire characteristics of a layered composite has been investigated in detail. 8552/IM7 prepregs were laid up to give unidirectional and quasi‐isotropic laminates. Specimen thickness (0.25 to 8.0 mm) and heat flux (15 to 80 kW/m2) were varied for irradiation. Fundamental reaction‐to‐fire properties of this composite are interpreted on the basis of the matrix components: epoxy resin and polyethersulfone. Cone calorimetry and temperature distributions through the laminate showed that the velocity and degree of combustion are dominated by fibre orientation for a given resin. In general, a quasi‐isotropic fibre orientation leads to faster ignition, because of preferred delaminations, but retards combustion processes more effectively than a unidirectional lay‐up. Migration velocities of the pyrolysis zone were measured. Copyright © 2011 John Wiley & Sons, Ltd.

A method based on micro attenuated total reflection (ATR) Fourier transform infrared spectroscopy (FTIR) is described to quantify inhomogeneity of plastic components in carbon fiber reinforced plastic material (CFRP). The investigated CFRPs contain an epoxy resin and a thermoplastic. Measurements on ground specimens at an inclined plane through the material allow the determination of the polymer distribution with a resolution of one micron regarding the depth. Three commercially available CFRPs (M18-1/G939, 8552/IM7, RTM 6) are characterized providing information on mechanical and thermal properties.

Summary Fundamental aspects for the thermal decomposition and formation of respirable fragments of carbon fibers are investigated to assess the health hazard of carbon fiber reinforced plastic material after a fire. The influence of temperature (600°C‐900°C)/heat flux (30‐80 kW/m2), time of thermal load (up to 20 minutes), and oxygen exposure is analyzed by means of mass loss and fiber diameter of intermediate modulus and high tenacity fibers with initial diameters of 5 to 7 μm. Various types and concentrations of flame retardants were tested with respect to fiber protection. Epoxy‐based composite specimens (RTM6/G0939) additionally containing aluminum or magnesium hydroxide and/or zinc borate (1‐25 wt% per resin) were analyzed by cone calorimetry. Carbon fiber decomposition increases with combustion/irradiation time and temperature/heat flux, after a threshold temperature (ca 600°C) is exceeded. Critical fiber diameters below 3 μm are reached within minutes and are predominantly observed close to the panel surface in contact with air. Effective fiber protection is achieved by flame retardants acting beyond 600°C, forming thermally resistant layers such as zinc borate. A new field of research is opened identifying flame retardants, which protect carbon fibers in carbon fiber reinforced plastic.

This study investigates one-sided thermal damage of carbon fiber reinforced polymers (CFRP) by means of depth resolved infrared spectroscopy, tomography and mechanical testing. All CFRP samples are thermally irradiated at one side with a heat flux of 50 kW/m2 over various time intervals. ATR-FTIR spectroscopy along a ground incline plane through the sample allows a chemical characterization of the thermal degradation of the polymer matrix into depth. Developing delaminations are observed with a depth-resolved gray-value-analysis of microfocused computed X-ray tomographic (µCT) data. Mechanical behavior is determined by tensile, compressive, and interlaminar shear strength (ILSS) testing of specimens taken from different depths of the irradiated samples. The depth profiles show how pronounced damage phenomena like matrix degradation and the development of delaminations are after one-sided thermal loading and how they influence strength in different ways. Compressive strength and ILSS is found to be more sensitive towards thermal damage than tensile strength, as they are most influenced by formed delaminations at higher thermal loads.