Title: Regularities of acoustic emission under shock loading of glass with a crack

Abstract

The acoustic emission (AE) method is widely used to control pressure vessels, pipelines, units and parts of critical structures, machines and mechanisms. Compared with other methods of non-destructive testing, it allows you to selectively detect the developing defects in the entire test object with fixedly installed sensors. For brittle destructible materials, the loading of which can lead to uncontrolled destruction, AE testing is of limited use. The aim of this work is a technique for detecting brittle developing defects in glass under impact using the method of AE and strain measurement. The experiments were carried out on a 2 mm thick sheet glass placed on a damping cardboard backing. An initial crack up to 5 to 15 mm in length was artificially created in glass samples. The impact was carried out by steel balls weighing 9 g. Glass deformations were recorded by a strain gauge system with a sampling rate of 64 kHz and 0.5 ppm relative strain units. AE signals were measured with a sampling frequency of 2 MHz and a detection threshold of 5 μV in the frequency range from 100 to 700 kHz. It has been experimentally established that in the process of impact action, the transverse shear of the cracks edges can reach 30 μm. Oscillations in the first 30 ms after the impact significantly exceed the level of AE signals. During the time from 100 to 600 s after the impact, relaxation of deformations to an equilibrium state by a logarithmic function of time is observed, associated with delayed fracture of the crack edges. A technique has been developed for detecting cracks in sheet glass under shock loading, based on the registration of AE signals of delayed fracture of the crack edges at the stage of stress relaxation.