The Use of Low Profile Piezoelectric Sensors for Impact and Acoustic Emission (AE) Detection in CFRC Structures

Abstract

This paper describes some of the issues that have been investigated as part of a programme called “DECODA” to develop low profile sensors for impact and Acoustic Emission (AE) detection in composite materials. Under the programme a number of sensing techniques are being investigated based upon piezoelectric, optical and Micro-machined Electro-Mechanical Sensor (MEMS) technologies. This paper concentrates on sensors based upon piezoelectric materials. As a comparison of the types of piezoelectric sensors available this study has looked at three types. The first two were based upon a 200 mm thick Lead-Zirconia-Titanate (PZT) ceramic and a 500 mm Calcium modified Lead-Titanate (PTCa-1)(qf)/epikote piezoelectric composite respectively, fabricated into what will be described as low profile sensors. As a comparison the third sensor was a commercially available broad band PZT transducer with an integrated amplifier built in (WDI-PAC ltd.). The results indicate that whilst the broad band sensors can be over 10 times as sensitive as the low profile sensors, the signals generated are potentially large enough to detect AE in composites. AE detection in Carbon Fibre Reinforced Composites (CFRC) is complicated in comparison with metallic structures due to the complex nature of AE propagation in anisotropic materials. A brief study of the complexities of AE propagation has shown that while these issues are a problem, AE detection and source location is still possible using real time algorithms. The biggest challenge is to be able to identify the key information from the AE source and separate out this information from signal shaping by the structure, sensor and processing hardware. It is desirable to be able to identify and size damage modes but as yet there does not appear to be enough understanding of composite AE for this to be possible in the near future.