Application of PVDF Film to Stress Measurement of Structural Member

In this paper a method to measure stress distribution using PVDF film and electrostatic voltmeter of non-contact type is developed. PVDF film is well suited to strain sensing applications for its excellent sensitivity and other good properties. The stress and strain distributions are determined from the measured potentials taking into account the piezoelectric constitutive law of film materials. First, in this paper the relationship between the electric potential and stresses is deduced in detail. Then, parameters used in the electric potential-stress relationship are estimated by an experiment applying the PVDF films to a smooth plate specimen. Next, a method to make isotropic piezoelectric material and a method too amplify the electric potential of the PVDF film by laminating two or more PVDF films together are also introduced and validated by experiment. Last, in order to check the accuracy of PVDF film as a stress measurement sensor, an experiment to measure the stress distribution of a plate specimen with an inclined crack is performed. The experimental results are in good agreement with those obtained from numerical calculation.