Innovative autonomous lead-free hybrid piezo-pyroelectric sensor for real-time wear assessment of disc brake pads

Abstract

This article investigates the capability of a autonomious sensor that uses piezoelectric and pyroelectric effects to detect wear on a pad. Analysis of the pressure exerted on the pad and the thermal power generated by friction describes variations in mechanical and thermal stresses at the surface of smart materials, influenced by velocity (v₀), deceleration (a₀) and pad thickness (e${}_{pad}$). Energy conversion material is bismuth titanate (BiT). A numerical model based on finite element analysis (FEA) correlates thermomechanical stresses with piezoelectric and pyroelectric conversions. The results demonstrate that a pressure down to -8 MPa with a deceleration of -10 m/s² induces a piezoelectric response of 9.5 V. BiT's electrical response varies according to pressure, enabling its estimation and control of the thermal effect. An increase in initial velocity amplifies BiT's electrical response, while a pyroelectric potential of 40 V is reached with a velocity of 50 m/s and a deceleration of -10 m/s². By varying the pad thickness from 3 to 15 mm, the pyroelectric response gradually decreases. Energy harvesting comprises a portion dissipated by the acquisition system and a portion stored to power the data-processing system, thus guaranteeing the sensor's autonomy.