Over the last ten years several observations have been made of compressive failure in glass by a so called fracture wave. A high-speed photographic study has been conducted in order to observe the propagation of fracture waves in glass. Streak and framing photography have been used to determine details of the wave speed and surface structure of fracture waves induced in glasses by planar impact. A 5 0 mm single stage gas gun was used to launch copper flyer plates at velocities of up to 1 km s-l. A computer controlled high-speed camera was used capable of exposure and interframe times from 5 0 ns upwards. Simultaneous measurements of the longitudinal stresses were made using manganin pressure gauges embedded in the samples. Results will be presented showing separation between the shock and fracture fronts suggesting that the failure mechanism is by compression rather than resulting from relief waves propagating from the free surfaces.1.
Commercial polyvinyliaene difluoride (PYDF) piezoe ectric I m was used to prodJce an inexpensive stress sensor wilh good spatial accLracy to measure the stress stale ben.nd a shock wave. The PUDF gauge was fOJnd IO respond within -100 ns lo fasl-rising pJlses. Since the gaige is p:ezoeleclr.c no power s,pply or amplifier was required lor the gauge. In order to measure last signals Ine gauge was foina to periorm besl :n the current mode in which the derivative of the stress was measired; tne s gnal %as tnen nLmerica1.y integrated. Signals were recorded on a fast (100 MS s-') storage oscil oscope. The gauges were calibrated against thin-foil manganin stress gauges to -2%. An app ical.on in rvhich the gauges were used to measure the response of an alumina lo shock loaaing is described.
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