3D Structural damage visualisation in fiber composites via a smart 3D capacitive printed sensor network

The ever-increasing use of composite materials in high-end structural applications calls for reliable damage diagnostics. This study proposes an innovative approach to convert a conventional glass fibre laminate into a multifunctional self-monitoring material without the need for external sensing systems. To this end, a single-walled carbon nanotube (SWCNT)-based ink is employed to establish parallel conductive paths onto glass fibre substrates via a versatile spray-coating method. The glass fibre fabrics are laid up in an alternating perpendicular direction to form a functional grid within the laminate, therefore imparting sensing capabilities. To ensure enhanced electrical performance a ternary nanomodified epoxy resin, comprising multi-walled carbon nanotube (MWCNTs) and carbon black (CB) as additives, is used. Laminates are subjected to ballistic impact, while impedance spectroscopy is utilised to detect the induced damage. The herein suggested configuration allows for localised monitoring at the intersection points of the sensing grid, thereby facilitating damage within the matrix and imparting self-sensing capabilities to the composite. Through the systematic processing of complex impedance data and the subsequent visualisation of the signal, a topographical representation of the affected area is produced. To validate the proposed damage detection methodology and strengthen the findings X-ray microcomputed tomography and infrared thermography are also employed. The successful implementation of damage mapping by exploiting a purposely designed multifunctional composite with inherent sensing capabilities demonstrates its potential as a reliable and effective Structural Health Monitoring (SHM) technique.