Micro-crack detection and assessment with embedded carbon nanotube thread in composite materials

Abstract

Carbon nanotube thread has shown strong promise to be built into or onto composite materials for strain and damage monitoring via the material’s piezoresistive property. It has been found that a distinguishing feature of sensing thread incorporated in these materials is the detection of micro-cracking. This study articulates how embedded carbon nanotube thread in unidirectional glass fiber composites can identify the onset of matrix cracking, track crack growth, and differentiate between crack breathing and closing states. This information is obtained by analyzing the resistance response of the thread with a low-speed data acquisition system and a simple Wheatstone bridge circuit. A digital optical microscope was utilized to verify that a micro-crack was indeed present in the structure at the location of the sensor thread. Additionally, to demonstrate the effectiveness of this crack detection approach compared to past crack detection approaches, a comparison against foil-type strain gauges and piezoelectric accelerometers was made. Finally, a simple crack model is presented for the sensor thread.