Study of brittle fracture by acoustic emission from indentation cracks

Abstract

This paper describes a novel approach for investigating the fracture of brittle solids by combining a theory of acoustic emission (AE) with the Dugdale–Barenblatt model. An example is provided with indentation-produced, half-penny-shaped cracks that were generated by pressing a Vickers indenter onto the surface of a glass plate and that produced AE signals. These were detected using four capacitive displacement transducers, one at epicenter and the other three at off-epicentral positions. Assuming that a mode I type of crack was generated and using indentation fracture mechanics, a mode I stress intensity factor KIc=7.44×105 N/m3/2 was obtained. Both dipole strength and source-time function associated with crack formation were determined from the AE theory. Assuming that an effective gauge length can be interpreted equal to a dipole linkage distance and using the Dugdale–Barenblatt model for the fracture of brittle solids, it is shown that all the other important parameters on crack formation can be determined. Included are the critical rupture stress σc=8.94 GPa, the crack tip opening displacement of 1.62 nm, the effective microstructural gauge length equal to 13.2 nm, and the time-dependent crack velocity as a function of a crack front radius.