Stress distribution and thermal environmental monitoring of structure by the use of piezoelectric and pyroelectric tape sensor

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Piezoelectric element PVDF film is polarized by the fluctuating strain when it is adhered on the surface of the structural member. Strain measurement is possible taking the piezoelectric constitutive law into account. Also, the PVDF film is applicable to the measurement of thermal environment by the pyroelectric property it possesses.In this research, a stress distribution measurement tape which can be used to measure the stress distribution along a specified line on the surface of structural member is mainly developed. The stress distribution measurement tape is an insulating adhesive tape on which rectangular PVDF films (5.0×2.5 mm) are repeatedly pasted with three inclination angles of 0, 45 and 90 degree to the direction of the tape length. Due to the property of piezoelectric material, each PVDF film will generates surface potential proportional to the applied strain after the tape is adhered onto a structural member. The surface potential can be measured by an electrostatic voltmeter of non-contact type. A tack-like electrode, a tack-pin electrode attached to the probe of the electrostatic voltmeter, is employed to measure the strain on the PVDF film within a small region. It plays a role to transfer the electric potential on the polarized surface of the piezoelectric element to the probe by electrostatic induction. Since there are no wiring works for each PVDF film, multi-point stress measurement can be achieved easily and conveniently. The applicability of such stress distribution measurement tape is verified through experiments on a notched specimen and a cracked specimen under constant cyclic loads. The measured distributions of σ_x, σ_y and τ_<xy> are compared with those calculated by FE analysis.