Monitoring of carbon fibre breakage in composites based on microwave emission

This paper presents a new method for fracture monitoring of carbon-fibre-reinforced polymer specimens based on the microwave emission from electrons accelerated between crack edges. The acceleration of the electrons was induced using a low voltage, which was applied to the fibre network of the specimen. A loss of network integrity occurs during crack formation in the fibres, and a potential difference appears between the crack edges. This potential difference causes an intensive field and fracto-emission from the surfaces of the broken carbon fibres and an acceleration of the emitted electrons in the crack. As a result, an intensive microwave emission from the accelerated electrons was detected over the frequency range from 8 to 12 GHz. The rise time of the detected microwave impulses is approximately a few nanoseconds. This time is in agreement with the crack formation time in a carbon fibre. The energy consumption minimum that is necessary to induce detectable microwave emission is approximately 1 mW/m2. This low energy consumption enables the use of the developed method for the health monitoring of large machinery components that are made from carbon-fibre-reinforced polymers.