High field behaviour of piezoelectric fibre composites

This paper analyses strain and polarisation responses of 1-3 composites, which are related to the fibre and matrix properties. The validity of equations that predict the strain and polarisation of fibres from composite responses, and associated errors at high electric driving fields, are discussed. Surface profile measurements of single PZT rods in a polymer matrix, subjected to a static voltage, were made to investigate the effect of fibre aspect (diameter to length) ratio. Surface profiles, which show the active PZT rod extending from the passive polymer matrix, agree well with predictions made using finite element analysis. The results show that for a 1-3 composite to be treated as a homogeneous medium the fibre aspect ratio needs to be low. Commercially available PZT-5A composition fibres fabricated using four production methods were incorporated into 1-3 composites with fibre volume fractions ranging from 0.02 to 0.72, and with various aspect ratios, were evaluated. Strain-field and polarisation-field curves for the composites were obtained by testing the composites under electrical field cycles of +/-2 kVmm(-1). From these curves the strain and polarisation response of the fibres have been extracted using appropriate analytical equations. The saturation strain, saturation polarisation and coercive field values are reported for the four fibre types. The Viscous Plastic Process (VPP) and Viscous Suspension Spun (VSSP) fibres develop strains of approximately 4000 ppm. Reduced piezoelectric activity is seen in extruded fibres, which develop strains of 3000 ppm.