Study and development of self-sensing composite materials

The aerospace sector is increasingly replacing metals with carbon fiber reinforced polymers (CFRPs) to reduce weight and emissions. However, CFRPs are vulnerable to barely visible impact damage, especially internal delamination, which can compromise structural integrity. Structural Health Monitoring (SHM) enables real-time damage assessment, but conventional embedded or surface-mounted sensors may degrade laminate strength by creating resin pockets or stress concentrations, particularly with brittle PZT materials. This research investigates minimally intrusive SHM solutions based on electrospun nanofibrous interleaves integrated within CFRP laminates. These nanofiber layers are designed to enhance interlaminar fracture toughness while enabling distributed sensing for impact and damage detection. By exploiting the intrinsic electrical conductivity of carbon fibers as built-in electrodes, the approach reduces the need for metallic components and other extraneous additions, preserving laminate performance. The work comprises six synergistic studies. First, the effect of rubbery nanofiber-mat thickness on mode I/II interlaminar fracture was assessed via mechanical testing supported by Acoustic Emission and fractography, clarifying how tailored interleaves enhance toughness and shape failure mechanisms. Second and third, model-based approaches were developed for piezoelectric sensing: multifunctional laminates with piezoelectric nanofiber interleaves were analyzed through lumped-circuit modelling to relate stacking parameters to electromechanical response. In parallel, a soft piezoelectric sensor for wearable/e-skin applications was fabricated, experimentally validated, and modelled to optimize acquisition settings over human-motion frequency ranges. Fourth, autonomous impact sensing in structural CFRP laminates was demonstrated through nanofiber interleaving without added insulation or conductive layers, while also improving impact resistance by mitigating delamination. Fifth, fully integrated midplane sensing layers enabled impact detection and localization using only laminate intrinsic components, offering slightly lower accuracy than PZT sensors but improved structural integrity and scalability. Finally, the ferroelectric behavior of self-sensing composites with piezoelectric-active nanofiber interleaves was investigated by varying poling parameters, and piezoelectric performance was quantified under compressive cyclic loading.