Damage detection and finite element modelling using a thermoformed electret as a polymeric piezoelectric sensor

Driven by the demand for efficiency, structural designs increasingly employ composite materials due to their superior stiffness and strength-to-weight ratios compared to metallic counterparts. In the automotive, aerospace, and space industries, composites have enhanced performance, reduced emissions, and lowered environmental impact. In commercial aviation, they reduce fuel consumption and operational costs while enabling the integration of embedded sensors and actuators, paving the way for smart structures capable of self-monitoring, adaptive control, and energy harvesting. Piezoelectric ceramics, such as lead zirconate titanate (PZT), are widely used as sensors and actuators owing to their high electromechanical coupling. However, their stiffness and brittleness limit their use in lightweight or flexible structures. To address these drawbacks, polymer-based piezoelectric materials have gained attention for their flexibility and toughness. This study investigates the application of a thermoformed electret as a piezoelectric sensor embedded in a laminated thermoplastic carbon fibre composite beam. Experimental modal analyses were performed under free and forced vibration using an impact hammer and a modal exciter. A Macro Fibre Composite (MFC) sensor and accelerometers were employed to obtain frequency response functions (FRFs). A concentrated mass was attached to the specimen to simulate damage by altering its dynamic behaviour. A finite element model was developed in Abaqus/Implicit to perform modal and harmonic analyses incorporating the electret sensor. Predicted FRFs agreed with experimental data, showing consistent frequency shifts and amplitude variations with increasing mass. The resulting damage indices rose proportionally with the simulated damage level, demonstrating the potential of thermoformed electrets as lightweight, flexible, and robust sensors for structural health monitoring in composite materials.