Source characterization of acoustic emission during indentation fracture of soda-lime glass

Abstract

Acoustic emission during Vickers indentation of soda-lime glass has been investigated and compared with the indentation fracture patterns. Acoustic emission waveforms measured by the conical piezoelectric transducer was shown to have the similar feature with the displacement waveform and to be useful for the characterization of source events using the short-term waveform. The final patterns of the indentation fracture, the shallow surface crack, the semi-circular median and the subsurface lateral cracks, did not vary with the peak indenter load. The crack arrest markings on the median crack surface showed a transient shape from circular to semi-circular at the peak indenter load higher than 2 kg, but below this load the circular crack arrest markings were not observed. The process of indentation fracture could be well represented by the in-situ acoustic emission. Accumulated acoustic emission increased with the peak indenter load and the indenter speed. Total ring-down counts, N, total event counts, $_Ne$, and total energy, ε, of the acoustic emission were found to be dependent on the characteristic crack dimension, c, as $N=αc^2.5$, $N_e=βc^1.9$, and $ε=γc^4.0$, where α, β, γ were the proportionality constants. A simple analysis was given to interpret this observation. The acoustic emission waveforms associated with the median and the lateral crack showed no distinctive feature, which could be concluded as the mode I microcracks. The waveforms associated with the radial crack showed the normal and inversed polarity, which was attributed the shear process of radial crack activation.