Experimental procedures for the observance of shear band formation during low velocity impacts

Woody, Diana L.

doi:10.1063/1.1143161

Cited by 4 publications

(2 citation statements)

References 12 publications

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“…1 The MWIR camera was specified by the manufacturer to produce single snapshots with a time gate of 0.48 μs, but in practical use 3 μs appeared to be needed to provide the full signal-capture capability. Thus, this MWIR camera could obtain an image, in single-image capture mode, as in the Woody studies, 13,14 with 3 μs time resolution, given proper synchronization and provided the hot spot was hot enough to produce significant thermal emission during that time window. We estimate, based on the results obtained here, that such highspeed single-image capture requires a minimum temperature of ∼460 K.…”

Section: A Ir Microscopy Apparatusmentioning

confidence: 99%

“…6,7 As a benchmark, it has been shown by calorimetry that RDX decomposes with a strong exotherm when heated to 530 K. 8 Almost all previous observations of hot spots in EM relied on visible emission techniques such as high-speed photography. 1,2,[9][10][11][12] Notable exceptions were two 1992 studies by Woody, 13,14 who used a fast IR detector array to obtain single time-gated images of shear bands created in salt crystals subjected to low-velocity impacts, and more recent works by Dickson and co-workers 15 and Perry and co-workers, 16 who studied impacted EM with a combination of visible and IR imaging.…”

Section: Introductionmentioning

confidence: 99%

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Hot spots in energetic materials generated by infrared and ultrasound, detected by thermal imaging microscopy

Chen

You

Suslick

et al. 2014

Review of Scientific Instruments

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We have observed and characterized hot spot formation and hot-spot ignition of energetic materials (EM), where hot spots were created by ultrasonic or long-wavelength infrared (LWIR) exposure, and were detected by high-speed thermal microscopy. The microscope had 15-20 μm spatial resolution and 8.3 ms temporal resolution. LWIR was generated by a CO2 laser (tunable near 10.6 μm or 28.3 THz) and ultrasound by a 20 kHz acoustic horn. Both methods of energy input created spatially homogeneous energy fields, allowing hot spots to develop spontaneously due to the microstructure of the sample materials. We observed formation of hot spots which grew and caused the EM to ignite. The EM studied here consisted of composite solids with 1,3,5-trinitroperhydro-1,3,5-triazine crystals and polymer binders. EM simulants based on sucrose crystals in binders were also examined. The mechanisms of hot spot generation were different with LWIR and ultrasound. With LWIR, hot spots were most efficiently generated within the EM crystals at LWIR wavelengths having longer absorption depths of ∼25 μm, suggesting that hot spot generation mechanisms involved localized absorbing defects within the crystals, LWIR focusing in the crystals or LWIR interference in the crystals. With ultrasound, hot spots were primarily generated in regions of the polymer binder immediately adjacent to crystal surfaces, rather than inside the EM crystals.

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Section: A Ir Microscopy Apparatusmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Hot spots in energetic materials generated by infrared and ultrasound, detected by thermal imaging microscopy

Chen

You

Suslick

et al. 2014

Review of Scientific Instruments

View full text Add to dashboard Cite

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Two dimensional infrared resolution of shear bands formed during low velocity impacts of NaCl crystals using fast infrared detectors

Woody

1992

Journal of Applied Physics

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NaCl crystals were subjected to low velocity impacts provided by a drop weight impact machine. The shear bands were imaged with the use of arrays of fast responding infrared detectors. The detectors monitored the amount of energy given off as infrared photons by the impacted crystalline solid. The main emphasis of this study was the real time observance of the shear band formation during the impact. The signal was recorded over the duration of the impact, heating I of the solid during its crushing, and the relaxation of the crystal. These crushing processes occurred over a 40-100 ,us timescale. Rapid infrared photons corresponding to shear banding were recorded on a 30-90 ns timescale.

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Drop hammer with high-speed thermal imaging

Men

Bassett

Suslick

et al. 2018

Review of Scientific Instruments

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The drop hammer test is the easiest way to assess the sensitivity of explosive materials, but drop hammer results for low-velocity impacts have not been able to explain how explosives will react to other kinds of initiating stimuli. In order to do that, we have to understand the fundamental mechanisms of drop hammer initiation and how they differ from other initiation methods. For this reason, there is interest in instrumented drop hammers that help reveal what the drop hammer does at a fundamental level. We have developed a drop hammer that combines two types of mid-wavelength infrared (MWIR) imagers that, when operated simultaneously, can detect both the rapid explosion and slower combustion from impact-initiated polymer-bonded explosives with high time (1 μs) and space (15 μm) resolution. Results are presented that show how to vibration isolate the drop hammer to minimize MWIR image shaking during impact and to quantify the noise floor for MWIR temperature determinations via optical pyrometry. Experiments were performed on polymer-encased crystals of RDX ([CH2–NNO2]3) and HMX ([CH2–NNO2]4). Our experiments showed that drop-hammer initiated explosions occur in two phases with roughly 100 μs between explosions. Drop-hammer initiation is compared to an ultrasonic hammer, which initiates explosions by rapid frictional rubbing of the explosive surfaces against the surrounding polymer. The explosion rise time is faster with the drop hammer because the drop hammer inputs energy throughout the explosive volume, whereas the ultrasonic hammer produces localized heating and much more heat at the explosive surface.

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Experimental procedures for the observance of shear band formation during low velocity impacts

Cited by 4 publications

References 12 publications

Hot spots in energetic materials generated by infrared and ultrasound, detected by thermal imaging microscopy

Hot spots in energetic materials generated by infrared and ultrasound, detected by thermal imaging microscopy

Two dimensional infrared resolution of shear bands formed during low velocity impacts of NaCl crystals using fast infrared detectors

Drop hammer with high-speed thermal imaging

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