Experimental investigation on porosity of carbon fiber-reinforced composite using ultrasonic attenuation coefficient

The present work experimentally investigates the correlations between ultrasonic attenuation coefficient and void content with the porosity 0.03%-4.96% of the carbon fiber-reinforced composite (CFRC) samples. The ultrasonic echo immersion bottom reflection technique with 5MHz flat probe is adopted to determine the attenuation coefficient and the metallographic microscope is used to measure the porosity destructively. A linear and a parabolic curve are found to be suitable to fit the data with the porosity 0.03%-0.5% and 0.5%-4.96%, respectively. It is observed that ultrasonic predictions accord with the microscopic results. The present data have been compared with the known testing models and empirical formulas. The power law between the attenuation coefficient and the porosity, the critical porosity phenomenon, and the effects of void morphology on ultrasonic attenuation have been discussed. This work not only provides experimental evidence in making clear the ultrasonic attenuation mechanism of pores, but also further proves that the attenuation coefficient could be used to nondestructively characterize the void content in composites.