Sensing of Damage Mechanisms in Fiber‐Reinforced Composites under Cyclic Loading using Carbon Nanotubes

Abstract

The expanded use of advanced fiber‐reinforced composites in structural applications has brought attention to the need to monitor the health of these structures. It has been established that adding carbon nanotubes to fiber‐reinforced composites is a promising way to detect the formation of microscale damage. Because carbon nanotubes are three orders of magnitude smaller than traditional advanced fibers, it is possible for nanotubes to form an electrically conductive network in the polymer matrix surrounding the fibers. In this work, multi‐walled carbon nanotubes are dispersed into epoxy and infused into a glass‐fiber preform to form a network of in situ sensors. The resistance of the cross‐ply composite is measured in real‐time during incremental cyclic tensile loading tests to evaluate the damage evolution and failure mechanisms in the composite. Edge replication is conducted to evaluate the crack density after each cycle, and optical microscopy is utilized to study the crack mode and growth. The evolution of damage can be clearly identified through the damaged resistance parameter. Through analyzing the damaged resistance response curves with measurements of transverse crack density and strain, the transition between different failure modes can be identified. It is demonstrated that the integration of an electrically conducting network of carbon nanotubes in a glass fiber composite adds unique damage‐sensing functionality that can be utilized to track the nature and extent of microstructural damage in fiber composites.

Investigation of electro-mechanical behavior of carbon nanotube yarns during tensile loading

“…Most of the research efforts to date have either been directed towards: 1) CNT based elements/patches [6] for external sensing and; 2) CNT based polymer nanocomposites and CNT based composites having CNT networks distributed throughout the bulk of the material [7][8][9][10][11]. In addition to these two well established research areas, more recent studies have been conducted on CNT based yarns [12] and CNT based sheets [13] for strain sensing.…”

Glass Fibers with Carbon Nanotube Networks as Multifunctional Sensors

“…Thostenson and Chou processed GFRPs with embedded CNTs in an epoxy matrix to evaluate the onset and evaluation of damage. [1,2,22] They showed that tracking direct current (DC) resistance changes during mechanical deformation is remarkably sensitive to the initial stage of matrix microcracking and could be used to identify the nature and progress of damage.…”

In situ strain monitoring of fiber-reinforced polymers using embedded piezoresistive nanocomposites

“…In the case of numerous piezoresistive materials presently investigated for strain sensing and structural monitoring applications, most of them often demonstrate linear strain sensitivities with a few demonstrating a bilinear sensitivity in dynamic or monotonic load tests [33,34,42,[47][48][49][50][51][52][53][54]. In these studies, the researchers typically report the gage factor in these linear regions using a least-squares linear fit to identify the slope (thus the gage factor).…”