Integrated active fibre composites elements for structural health monitoring in glass fibre reinforced laminates

摘要

Active Fibre Composites (AFC) elements consist of piezoelectric ceramic fibres embedded between two interdigitated electrodes in a thermoset polymer matrix. A deformation of the piezoelectric AFC elements by external forces generates a voltage across the electrodes that can be recorded. Acoustic Emission (AE) analysis is a well established method for structural integrity monitoring of composite structures and elements. AFC elements can detect acoustic waves in structural elements analogous to conventional commercial AE sensors. Experimental results using AFC elements as AE sensors integrated into glass fibre reinforced epoxy (GFRP) laminates and polymethyl methacrylate (PMMA) plates are presented. Their AE sensor properties are compared for three coupling conditions: a) integrated into the test plates, b) permanently bonded on the surface of the test plates, and c) reversibly mounted on the plates. The performance of the AFC elements in case c) is also compared with that of reversibly mounted commercial AE sensors. The sensitivity of the AFC elements is higher along the direction of the piezoelectric fibres than normal to it and at least comparable or slightly higher than that of the reversibly mounted conventional AE sensors. A definite increase in sensitivity is achieved by bonding and integration. Further, the results show that integrated and/or bonded AFC elements fulfil the basic requirements for use in the structural health monitoring of composite structures.