Experimental investigations of the internal friction of optical and technical glasses with a flexure pendulum equipment

Abstract

A special flexure pendulum equipment for investigation of the mechanical relaxation behaviour (internal friction) of glasses, glassceramics and other materials is presented. With the help of this apparatus it is possible to investigate the internal friction in the temperature ränge from room temperature until beyond Tg with a frequency of about 1 Hz. For analyzing the experimental results the shear behaviour of the investigated material is described in terms of a Maxwell body characterized by the rheological parameters Young's modulus and relaxation time. From the theoretical treatment of the bending problem for the experimental equipment calculation, formulae are obtained which connect the rheological parameters with the measured quantities period of oscillation and logarithmic decrement. Investigations of the internal friction of optical and technical glasses show weak effects in the ränge from room temperature until Tg and very strong damping peaks with different peak widths and maxima temperatures in the ränge beyond Tg. The syntheses and glass transformation ranges of the investigated glasses are very different. The activation energies of the hightemperature relaxation processes are obtained from the measured temperature dependences of relaxation times. These activation energies of the high-temperature relaxation process beyond Tg are smaller than the activation energies of viscosity determined by means of a bar elongation method.