Abstract
Flexoelectric effects hold promising applications in sensing, actuating, and energy capturing, and thus it is demanded to measure the flexoelectric coefficient tensors of dielectric materials accurately. In this work, an approach to measuring the effective flexoelectric coefficient tensor component μ2312 of polymeric materials is developed by imposing a torque load upon a half cylindrical specimen. It is proven that μ2312 can be calculated by assessing the electric charge on the axial plane and the strain gradient along the radial direction, both induced by the torque. To overcome the difficulty in experimental measurements, the relationship between the strain gradient and torque is deduced theoretically and further verified with finite element analysis. This approach is applied to testing bars machined from bulk polyvinylidene fluoride (PVDF). Potential errors from the piezoelectric effects and the non-uniform strain gradient are discussed to verify the validity of the measurement. The experimental results show good reproducibility and agreement with other measured effective flexoelectric tensor components of PVDF. This work indicates a potential application of PVDF-based mechanical sensors and provides a method to investigate the effective flexoelectric coefficient component of polymers.
Highlights
Flexoelectric effects hold promising applications in sensing, actuating, and energy capturing, and it is demanded to measure the flexoelectric coefficient tensors of dielectric materials accurately
An experimental process to measure the 2312 component of the flexoelectric coefficient is proposed and applied to investigate the flexoelectricity of un-polarized polymer polyvinylidene fluoride (PVDF). It is verified in the cylindrical coordinate system that μ2312 can be obtained by measuring the electric charge in the axial plane of a half-cylinder shaped bar induced by pure torque
The relationship between the shear strain gradient along the radial direction and the torsional moment is presented through a simple method of elastic mechanics deduction based on the plain stress assumption due to the application conditions
Summary
Flexoelectric effects hold promising applications in sensing, actuating, and energy capturing, and it is demanded to measure the flexoelectric coefficient tensors of dielectric materials accurately. To overcome the difficulty in experimental measurements, the relationship between the strain gradient and torque is deduced theoretically and further verified with finite element analysis This approach is applied to testing bars machined from bulk polyvinylidene fluoride (PVDF). These perovskite ceramics are measured to be four or five orders of magnitude higher than the simplified model, and flexoelectricity based sensing devices are proposed and demonstrated[14,15,16,17,18,19,20,21]. Experimental approaches have been developed to assessing the flexoelectric coefficient components μ1211 and μ3121 of polymers As an example, these methods were applied to PVDF, and μ1211 and μ3121 were measured in the magnitude of 10−10 C/m and 10−8 C/m, respectively[28,29,30]. Unlike inorganic crystals in which elastic and plastic strains can be clearly defined, the deformation mechanism in polymers, as stated previously, is more complicated, and the measured strain εij is not directly related to the chemical bonding configurations
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