Failure waves in glass under dynamic compression

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Abstract
Plate impact (I-d strain) and bar impact (I-d stress) experiments were performed on soda lime glass and pyrex glass. Embedded manganin gauges were used to monitor stress-time profiles in both types of experiments. In the plate impact experiments we found that glass not only fails through inelastic (or densification) deformation, but also through a unique failure process which gives rise to a failure wave first observed by Kanel et al. in the Soviet Union in 1990. In the present work three independent observations were made that support the existence of failure wave in glass: (i) the spall strength below and above the HEL is zero behind the failure wave, (ii) a small recompression is present in the longitudinal gauge (embedded between glass and PMMA) profile due to the reflections of release waves from the advancing failure wave, and (iii) transverse stress (measured by transverse gauge) increases on the arrival of the failure wave. The transverse stress increases because the glass loses its shear strength as a result of the arrival of the failure wave. The speed of the failure wave is about 1.5–2mm/μs. In the experiments on pyrex bars we used high speed Imacon framing camera to monitor the speed of the failure front. We found that pyrex bars fail through a failure front propagating across the cross section of the bar. The speed of the failure front is a function of the impactor (pyrex bar or steel plate) velocity. The speed increases from 2.3 mm/μs, corresponding to impact velocity of 125 m/s, to 5.2mm/μs for impact velocity of 330 m/s.

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