PROPAGATION MECHANISM OF ULTRASONIC-WAVES IN POROUS CERAMICS

In this paper, we present a probabilistic theory of propagation of ult rasonic waves in porous ceramics, and propose a new method of ultrason ic inspection for nondestructive pore characterization. The idea is ba sed upon the arrival probability of ultrasonic rays. When incident ray s impinge on a pore, they travel around the pore surface and increase the propagation time. We studied this process probabilistically, and f ound that the propagated waveforms can be expressed as Gaussian functi ons. The Gaussian waveform is determined by the porosity, pore size an d pore shape. This new finding led to the following important laws. (1 ) The delay time of an ultrasonic wave passing through porous ceramics is proportional to the porosity. (2) The pulse width of the wave incr eases with increasing mean pore size. (3) The amplitude of the wave de creases with mean pore size. (4) The delay time and pulse width of the wave increase as the mean pore perimeter increases. Formulae for thes e relationships between ultrasonic and pore characteristics were deriv ed, and an ultrasonic method for evaluating porosity and pore size was proposed.