On the material properties and constitutive equations of piezoelectric poly vinylidene fluoride (PVDF)

The complex elastic and piezoelectric material properties of uniaxially oriented PVDF were measured over a temperature range of 20°C to 80°C and a frequency range of 0.01 Hz to 100 Hz using specially developed equipment. A WLF Time-Temperature Superposition (TTS) expansion of the resulting data confirmed previously reported thermorheologically simple (TRS) behavior for the elastic properties and established that the piezoelectric behavior is also TRS. The form of the piezoelectric TTS expansion was identical to that of the elastic expansion, implying that the mechanisms responsible for viscoelastic behavior are also responsible for visco-piezoelectric behavior. A modified Arrhenius equation was developed to allow a broader TTS expansion. Empirical equations describing both viscoelastic and piezoelectric properties over temperature and frequency were constructed using these expansions and compared to measured data.; The dielectric properties of PVDF were measured over the range of −60°C to 80°C and from 20 Hz to 1MHz. Cole-Cole and Vogel-Fulcher equations were combined and the resulting dielectric equations were confirmed by comparison to measured data.; All material property relationships were assembled into a constitutive framework for piezoelectric materials in the frequency domain. A novel technique was employed to test the ability of the elastic, piezoelectric, and dielectric property equations to predict behavior outside of the measured temperature/frequency range with excellent results.