Investigation on GNP layer as protection against high thermal fluxes in CFRP composites
Topic(s) : Material and Structural Behavior - Simulation & Testing
Co-authors :
Fabrizia CILENTO (ITALY), Barbara Palmieri (ITALY), Leone CLAUDIO , Genna SILVIO , Michele GIORDANO (ITALY), Alfonso MARTONE (ITALY)Abstract :
The demand for lightweight multifunctional materials as coatings of composites is increasing in the automotive and aerospace industries. Polymer-based composite materials exhibit poor performance when exposed to high temperatures, mainly due to the decomposition of the organic matrix, which impairs the material’s mechanical performance. In this work, graphene nanoplatelet (GNP)/epoxy nanolayered films are evaluated as barrier coatings to radiative thermal fluxes (TBCs) to mitigate the thermal degradation of Carbon Fibres Reinforced Plastic (CFRP) [1].
The GNP protective film was bonded on the surface of the CFRP laminate with a compression moulding process using a platen press and cured for 1 hour at 120°C with a pressure of 3 bar. Samples protected with #1 GNP layer (60 µm thickness) and #2 GNP layers (120 µm thickness) have been fabricated and tested. The performance of CFRP composite to high-power radiative heat flux has been investigated by laser spot heating tests of a duration of 15 min and magnitudes ranging from 25 to 150 kW/m2 and the post-heat mechanical response has been assessed through flexural elastic modulus and post-heat interlaminar shear strength (ILSS).
A significant reduction of the maximum temperatures on the heated surface and the damaged area is observed in the protected samples when exposed to heat fluxes compared to the unprotected CFRP. This effect improves with increasing level of protection from #1 to #2 GNP-layers (Figure 1). Mechanical tests on burned samples at 100 kW/m2 showed a significant increase of the post-heat flexural elastic modulus and post-heat ILSS in the case of the sample with one GNP-layer protection of +260% and +90% respectively compared to the unprotected sample [2].
The effectiveness of the coating protection from radiative thermal fluxes is due to its dual function of shielding and diffusing heat. The low emissivity of the GNP layer only allows a partial absorption, about 45%, of the incident radiant energy. The absorbed energy is then distributed over the surface of the GNP film, rather than the CFRP sample, thanks to the high anisotropy between the in-plane and cross-plane thermal conductivities. Therefore, the two mechanisms concurrently contribute to significantly reduce the thermal degradation of the material.
The GNP protective film was bonded on the surface of the CFRP laminate with a compression moulding process using a platen press and cured for 1 hour at 120°C with a pressure of 3 bar. Samples protected with #1 GNP layer (60 µm thickness) and #2 GNP layers (120 µm thickness) have been fabricated and tested. The performance of CFRP composite to high-power radiative heat flux has been investigated by laser spot heating tests of a duration of 15 min and magnitudes ranging from 25 to 150 kW/m2 and the post-heat mechanical response has been assessed through flexural elastic modulus and post-heat interlaminar shear strength (ILSS).
A significant reduction of the maximum temperatures on the heated surface and the damaged area is observed in the protected samples when exposed to heat fluxes compared to the unprotected CFRP. This effect improves with increasing level of protection from #1 to #2 GNP-layers (Figure 1). Mechanical tests on burned samples at 100 kW/m2 showed a significant increase of the post-heat flexural elastic modulus and post-heat ILSS in the case of the sample with one GNP-layer protection of +260% and +90% respectively compared to the unprotected sample [2].
The effectiveness of the coating protection from radiative thermal fluxes is due to its dual function of shielding and diffusing heat. The low emissivity of the GNP layer only allows a partial absorption, about 45%, of the incident radiant energy. The absorbed energy is then distributed over the surface of the GNP film, rather than the CFRP sample, thanks to the high anisotropy between the in-plane and cross-plane thermal conductivities. Therefore, the two mechanisms concurrently contribute to significantly reduce the thermal degradation of the material.