Statistical kinetics of micro-failure of heterogeneous materials

Abstract

The AE method permits conducting a differentiated study of the kinetics of crack formation in loaded composite materials. The generation of microcracks is like a statistical process. The study of the time intervals Δt between the successive acts of microfailure revealed two types: individual and collective breaks. For the individual microcracks, the distribution of Δt is exponential with a coefficient of variation of v1=1. The average value of Δt1 at the beginning of loading (with a constant rate of deformation) is not dependent on the time, but decreases with an increase in t before failure of the sample. In collective rupture of a group of elements in the material (revealed by the anomalously small ratio of the amplitude of the acoustic signal to its duration), the exponential distribution is invalid and the coefficient of variation is vc>1. Before failure of the sample, the coefficient of variation of the intervals between individual breaks vi increases sharply and attains (or exceeds) the corresponding value of vc for collective breaks. This is caused by the transition from delocalized accumulation to the stage of the formation and increase in the focus of failure during crack formation.