Interlayer Strain Monitoring of Hybrid Composites With Carbon Nanofiber Paper Using Fiber Bragg Grating Sensors

Graphite/epoxy prepregs are typically used to manufacture aerospace composite structures through autoclave processing. However, the vacuum-assisted resin transfer molding (VARTM) process has recently received increasing attention as a low-cost method to fabricate quality aerospace structures. In this study, carbon nanofiber paper was integrated into composite laminates using the VARTM process. The carbon nanofiber paper has a porous structure with highly entangled carbon nanofibers. The carbon nanofiber paper can be employed as an inter-layer and surface layer to enhance the damping properties of the nanocomposites. To study the integration performance of nanocomposites with nanofiber paper layer, Fiber Bragg Grating (FBG) sensors were embedded into interlayers of the composite. Two kinds of nanocomposite specimens with FBG sensors were designed and fabricated to study the strain distribution characteristics among different layers. The interlayer strains in under static loads were measured simultaneously to test whether nanofiber paper can be successfully integrated into glass fiber composite. The test results show the two different layers of nanofiber paper and glassfiber are fully integrated to the composite. In addition, a novel tensile test of carbon nanofiber paper-enabled nanocomposites using FBG sensors was conducted to demonstrate the bonding strength between the nanofiber paper layer and the glassfiber layer. The scanning electron microscopy (SEM) technique was conducted to investigate the impregnation of carbon nanofiber paper and FBG sensors by the resin during the VARTM process. The study shows that a complete penetration of the resin through carbon nanofiber paper and FBG sensors was achieved.