Direct 3D Printing of Strain Sensors onto 3D Woven Orthogonal Composite Structures: Evaluating Two Distinct Approaches for Sensor Performance

In industries relying on the structural integrity of composites, such as aerospace, integration of Carbon Nanotube (CNT) sensors within Structural Health Monitoring (SHM) systems emerges as a pivotal strategy for real-time damage detection and assessment. The versatility of the CNTs extends to various surfaces, including textiles and plastics, through different manufacturing techniques. This study introduces a novel sensor system for SHM applications, using conductive patterns of CNT-reinforced high-performance polymers integrated into 3D orthogonal woven fabrics (3D-ORT). The 3D-ORT fabrics woven with E-glass fibers served as a substrate for the sensors. Two distinct approaches for sensor integration were explored: direct 3D printing onto 3D-ORT composites and printing onto 3D-ORT fabric, followed by composite production through vacuum infusion process. The former approach faced challenges in interfacial bonding, while the latter showed robust adhesion and integration. Piezoresistive behavior analysis revealed a correlation between CNT concentration and strain-induced changes in electrical resistance. In addition, the study investigated the impact of sensor length on electrical resistance, highlighting a direct relationship between length and resistance sensitivity. The potential of this approach lies in its ability to create a piezoresistive self-sensing system with effective stress transfer for sensitive strain and pressure measurement, particularly in SHM applications.