Scalable Process for Embedding Strain Gauge Sensors in Epoxy-Fiberglass Composites: Toward Next-Generation Smart Fiber-Reinforced Polymers

Structural health monitoring (SHM) is a rapidly advancing field that focuses on the detection and analysis of defects in engineering structures. To meet the demand for lightweight and high-performance materials, composites are increasingly used in place of metals or plastics. This study introduces a manufacturing process based on transfer printing to embed strain gauge sensors into epoxy-fiberglass composites. The process ensures minimal intrusiveness (<15 μm), low-cost processing, and high scalability. The transfer printing technique enables gentle integration of thin-film sensors directly onto fiber preforms, prior to composite infusion. The sensor architecture ranges from a single layer to multilayer configurations, including silver electrodes and a carbon-based sensing layer with a gauge factor of ∼30 under tensile and compressive strains between −1.5 and 1.5%. Electrical tests reveal excellent linearity (R2 > 0.995), mechanical stability over more than 700 cycles, and negligible drift during curing, confirming the robustness of the embedded devices. This approach demonstrates the feasibility of integrating functional electronics into fiber-reinforced composites, paving the way for next-generation intelligent structures in SHM applications.