System for Logging Acoustic Emission Signals from FRP Reinforcing Rods that is Suitable for Field and Long Term Laboratory Testing

Abstract

Fibre reinforced polymer (FRP) rods have seen increasing use in civil infrastructure applications. FRP rods are corrosion resistant and are easier to handle than steel. They have been used in over 190 projects including many bridge decks and traffic barriers. However, at sufficiently high loads (more than ~25% of the ultimate load) FRP rods can become susceptible to creep failure. In addition, FRP rods have linear stress strain relationships up to failure and hence mechanical property changes to do provide a reliable indicator of failure. To study and monitor failure in FRP rods acoustic emission has been used as a diagnostic tool. Acoustic emission signals characteristics can be correlated with the level of stress within the FRP rod. For example, signal entropy has proven to be a good indicator of the stress level in glass and carbon FRP rods. However, due to the high sampling rates in AE signal acquisition, signal analysis has required post processing of signals. For longer term field and long-term laboratory studies, it is not practical to record and post process the data from the AE signals, which is produced at several megabytes per second. In this work we describe a system that uses triggered recording of the AE signals so that only the signal for a few milliseconds are logged in the vicinity of each AE event. The system is microcontroller based and allows for sampling at ~700k samples per second, with logging to SD cards. The system is suitable for deployment at a large number of nodes. Examples of the system being applied to AE monitoring of glass FRP rods will be shown. The system will be used for longterm laboratory studies of FRP rods at low load levels (less than 50% of ultimate).