Direct-write piezoelectric ultrasonic transducers for impact damage detection in composite plates

Internal damage in carbon-fibre reinforced polymer (CFRP) plates, induced by low velocity impact, becomes important to be detected and repaired before catastrophic failure happens. In this context, structural health monitoring (SHM) techniques have been developed that could monitor a structure over time by using a network of sensors. Discrete ultrasonic transducers made of piezoelectric lead zirconate titanate (PZT) ceramic, as currently widely used for SHM purpose, can generate and sense guided ultrasonic waves traveling in the structure. These waves are particularly affected by damage and discontinuities, but also by the anisotropy and complex structure of CFRP. Direct-write (DW) piezoelectric ultrasonic transducers have been developed on metallic structure for SHM to reduce transducers weight and profile for potential aircraft applications, to improve system reliability and to reduce the cost of introducing a large number of transducers, while they are directly produced during manufacturing process of the structure to monitor. The aim of this study is to develop the DW transducers and demonstrate their applications on a CFRP plate. DW piezoelectric transducers have been fabricated by spraying of silver electrode and layer of poly(vinylidene fluoride-trifluoroethylene) P(VDF-TrFE). It is shown that these new transducers achieved good piezoelectric response, suitable for Lamb waves generation.