Transfer printed laser induced graphene strain gauges for embedded sensing in fiberglass composites

The continuous monitoring of strain in fiber-reinforced composites while in service typically requires bonding a network of sensors to the surface of the composite structure. To eliminate such needs, and to reduce bulk and limit additional weight, this work utilizes the transfer printing of laser induced graphene (LIG) strain gauges onto the surface of commercial fiberglass prepreg for the in situ self-sensing of strain. The resultant embedded strain sensor is entirely integrated within the final composite material, therefore reducing weight and eliminating limitations due to external bonding compared to current alternatives. Additionally, the simple printing process used here allows for the customization of the size and sensing requirements for various applications. The LIG strain sensor is shown to be capable of tracking monotonic cyclic strain as shown during tensile loading and unloading of the host composite, while also proving capable of tracking the dynamic motion of the composite which is characterized via frequency response and sinusoidal base excitation. The LIG strain gauge in this work can thus be used for tracking either quasi-static or dynamic variations in strain for the determination of the deformation experienced by the material, as well as the frequency content of the material for structural health monitoring purposes.