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

压电元件PVDF薄膜附着在结构构件表面时，会受到波动应变的极化作用。考虑到压电本构关系，应变测量是可能的。同时，由于PVDF薄膜所具有的热释电特性，它还适用于热环境的测量。在本研究中，主要开发了一种可用于测量结构构件表面沿指定直线的应力分布的应力分布测量带。应力分布测量带是一种绝缘胶带，在其上重复粘贴长方形PVDF薄膜(5.0×2.5 mm)，沿胶带长度方向有0、45和90度三个倾角。由于压电材料的特性，将胶带粘贴到结构构件上后，每个PVDF薄膜都会产生与施加的应变成正比的表面电势。表面电势可用非接触式静电伏特计测量。在静电电压计的探头上安装了一个针状电极，用来测量PVDF薄膜在小范围内的应变。它的作用是通过静电感应将压电体极化表面上的电势传递给探头。由于不需要对每个PVDF薄膜进行布线，因此可以方便地实现多点应力测量。通过在恒定循环载荷作用下的缺口试件和裂纹试件的试验，验证了这种应力分布测量带的适用性。将σ_x、σ_y和τ_&lt；xy&gt；的测量分布与有限元计算结果进行了比较。

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.