Title: Mode II Delamination Detection in Laminated Composite Materials Using Carbon Nanotube Yarn: State-of-the-Art and Challenges
composites

Authors:
J. L. Abot, K. Wynter, M.-D. Lamos,
Department of Mechanical Engineering, The Catholic University of America, Washington, DC 20064, USA

K. Belay,
Department of Physics, Florida A&M University, Tallahassee, FL 32307, USA

G. Seidel, B. Vondrasek
Aerospace & Ocean Engineering Department, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA

ABSTRACT
The use of piezoresistive carbon nanotube thread sensors that can be integrated and highly distributed in large structures may offer a robust structural health monitoring method for polymeric and composite materials. Carbon nanotube forests can be spun into a yarn that is tough and electrically conductive. This carbon nanotube yarn was integrated into polymeric and composite materials and used for the first time as a sensor to monitor strains and detect damage including delamination through resistance measurements. Carbon nanotube yarns have a piezoimpedance property that depends on the exact construction of the material including the nanotube geometry, degree of tension and twist of the yarn, and resistance characteristics of the yarn. Furthermore, they maintain the integrity of the host materials without adding weight or altering its integrity due to their micron-size dimensions. The sensor yarn was embedded throughout composite material samples creating self-sensing composites. Any damage located near the CNT thread yarn causes its resistance to change and thus could be detected. The authors had previously demonstrated that the sensor yarn detected mode I and mode II interlaminar delamination in self-sensing composites of different fiber architectures and materials. This paper includes results of sensor yarns that are integrated in glass fabric polymeric composite material samples. This correlation information is used to determine the required density and spacing of the sensor threads to guarantee the detection of delamination of a specific size and at a specific location. Experimental data is presented for glass/epoxy laminated composites including the mechanical load versus deflection curves, the electrical resistance data of the sensor threads. This information is also used to create a “delamination map” of the actual sample and could be adapted to that of any composite structure. These self-sensing composites are very sensitive to delamination and may help to revolutionize the maintenance of composite structures that could now be based on their condition and not their amount of use.