Electro-thermal damage of carbon fiber/epoxy composite laminate

The present work concentrates on the electro-thermal damage mechanism of carbon fiber/epoxy composites subjected to ampere-level Direct Current (DC) currents. A new fully automated electro-thermal tester that enable one to inject currents through the composites and measure the surface temperature in real time has been developed. The DC electrical conductivity and dielectric properties of electrified composites have been investigated, in order to develop a nondestructive testing method for electro-thermal damage. Additionally, Fourier Transform Infrared Spectroscopy (FT-IR), Dynamic Mechanical Analysis (DMA), flexural properties, surface morphology analysis, and Scanning Electron Microscope (SEM) were conducted to exploit in-depth the damage mechanism of electrified composites. Results show that the electrical conductivity is decreased with increasing currents, resulting from the modification of the fiber-to-fiber conduction paths. With higher currents the dielectric properties are apparently enhanced, and this case can be explained by interfacial polarization that arises from the microcracking induced by the residual thermal stress. The dielectric loss tangent can be regard as a characteristic parameter of electro-thermal damage. Furthermore, the deterioration of flexural performances is attributed to the microcracking, which is proved to be the major damage mechanism. High-intensity currents application has an effect of post-curing and physical aging, which significantly increases the glass transition temperature and suppresses the further formation of micro damage.