ELECTRICAL SELF-SENSING OF PULSED LASER ABLATION IN NANOFILLER-MODIFIED COMPOSITES Rajan Jain Hashim Hassan Weinong Chen Tyler N. Tallman School of Aeronautics and Astronautics Purdue University West Lafayette, Indiana 47907 Nesredin Kedir School of Materials Engineering Purdue University West Lafayette, Indiana 47907 ABSTRACT Laser-to-composite interactions are becoming increasingly common in diverse applications such as diagnostics, fabrication and machining, and weapons systems. Despite a lack of physi- cal contact, lasers can induce seemingly imperceptible structural damage to materials. In safety-critical venues like aerospace, automotive, and civil infrastructure where composites are play- ing an increasingly prominent role, it is desirable to have means of sensing laser exposure on a composite material. Self-sensing materials may be a powerful method of addressing this need. Herein, we present an initial exploratory study on the potential of using changes in electrical measurements as a way of detect- ing laser exposure to a carbon nanofiber (CNF)-modified glass fiber/epoxy laminate. CNFs were dispersed in liquid epoxy resin prior to laminate fabrication via hand layup. The dispersed CNFs form a three-dimensional conductive network which al- lows for electrical measurements to be taken from the tradition- ally insulating glass fiber/epoxy material system. It is expected that damage to the network will disrupt the electrical pathways, thereby causing the material to exhibit slightly higher resistance. To test laser sensing capabilities, a resistance baseline of the CNF-modified glass fiber/epoxy was first established before laser exposure. The specimens were then exposed to an infra-red laser operating at 1064 nm, 35 kHz, and pulse duration of 8.2 ns. The specimens were irradiated for a total of 20 seconds (4 exposures each at 5 seconds). The resistances of the specimens were then measured again post-ablation. It was found that the average re- sistance increased by about 18 percent. This established that the laser was indeed causing damage to the specimen sufficient to evoke a change in electrical properties. To expand on this result, electrical impedance tomography (EIT) was employed for local- ization of 1, 3, and 5-second laser exposure on a larger speci- men. EIT was not only successful in detecting damage that was virtually imperceptible to the human-eye, but it also accurately localized the exposure sites. The post-ablation conductivity of the exposure sites decreased in a manner that was comparable to the resistance increases obtained during prior resistance change testing. Based on this preliminary study, this research could lead to the development of a real-time exposure detection and tracking system for the measurement, fabrication, and defense industries. Keywords: nanofiller-modified composites, laser exposure, pulsed laser ablation, electrical impedance tomography, self- sensing material NOMENCLATURE t τ thermal relaxation time f rep repetition rate T l pulse duration σ domain conductivity φ domain voltage z l contact impedance between the l th electrode and domain n outward pointing normal vector V l voltage on the l th electrode Proceedings of the ASME 2021 Conference on Smart Materials, Adaptive Structures and Intelligent Systems SMASIS2021 September 14-15, 2021, Virtual, Online SMASIS2021-67779 Copyright © 2021 by ASME V001T08A005-1 Downloaded from http://asmedigitalcollection.asme.org/SMASIS/proceedings-pdf/SMASIS2021/85499/V001T08A005/6776583/v001t08a005-smasis2021-67779.pdf by Purdue University at West Lafayette user on 26 October 2021