A dynamic flexural rigidity apparatus with electrostatic excitation

An apparatus is described for measuring the dynamic flexural rigidity, and elastic and loss moduli, of thin materials through the method of resonance vibration, excited by electrostatic forces. An earthed specimen is placed between two electrodes, to which a balance alternating potential up to 4 kv with a positive bias of 500 v is applied from an oscillator via a push-pull amplifier. Provision is made for fine control of the electrode spacing and for accurate positioning of the specimen in any direction. The apparatus has been found suitable for various materials of rigidities up to 10⁷ dyn cm². For specimens more than 0.08 mm thick vibrating at over 80 c/s, air damping produces little shift in the resonant frequency. The bandwidth, however, is markedly affected by air, which must be evacuated in the determination of loss modulus.