Piezoelectric Response of Polyvinylidene Fluoride to Combined Compression and Shear.
Technical rept. 1 Jul 84-31 Dec 85,
SRI INTERNATIONAL MENLO PARK CA
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In this project we performed inclined-impact wave propagation experiments to assess the shear-stress sensitivity of the piezoelectric polyvinylidene fluoride PVDF sensing element of the National Bureau of Standards NBS soil stress gage. No sensitivity to shear stress was expected. However, because of deficiencies in the general understanding of the piezoelectric response of PVDF, especially under large stresses and strains, direct measurements were necessary to confirm this expectation. In a set of four plate-impact experiments, we investigated one combination of stress wave amplitudes a 4.5-kbar 450 MPa compressive stress and a 0.22-kbar 22 MPa shear stress. The results are ambiguous and inconclusive. However, we could detect no piezoelectric sensitivity of the PVDF to in-plane shear stress. From this observation, we make a tentative estimate that the piezoelectric sensitivity of the NBS PVDF sensing element to in-plane shear stress is less than 0.27 times its sensitivity to hydrostatic compression. We discuss the uncertainties in the experiments and review the outstanding questions concerning the piezoelectric response of PVDF. We suggest two experimental methods that could usefully augment the observations that can be made from inclined-impact experiments.
- Test Facilities, Equipment and Methods
- Electricity and Magnetism