Thermal and mechanical response of PBX 9501 under contact excitation

Mechanical action can produce dramatic physical and mechanochemical effects when the energy is spatially or temporally concentrated. An important example of such phenomena in solids is the mechanical initiation of explosions, which has long been speculated to result from 'hot spot' generation at localized microstructures in the energetic material. Direct experimental evidence of such hot spots, however, is exceptionally limited; mechanisms for their generation are poorly understood and methods to control their locations remain elusive. Here we report the generation of intense, localized microscale hot spots in solid composites during mild ultrasonic irradiation, directly visualized by a thermal imaging microscope. These ultrasonic hot spots, with heating rates reaching B22,000 K s À 1 , nucleate exclusively at interfacial delamination sites in composite solids. Introducing specific delamination sites by surface modification of embedded components provides precise and reliable control of hot spot locations and permits microcontrol of the initiation of reactions in energetic materials including fuel/oxidizer explosives.

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“…7e,f). Recent work has examined ultrasonic heating of EMs (mostly with small temperature rises) and analysed its frequency dependence 32,33 .…”

Section: Resultsmentioning

confidence: 99%

Ultrasonic hammer produces hot spots in solids

et al. 2015

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“…The authors also observed that heat generation exceeded the predicted viscoelastic heating responses at high solids loading, suggesting a secondary mechanism attributed to particle interactions. Mares et al 13 have shown evidence of heat generation within an energetic composite material, PBX 9501, excited at frequencies from 50 kHz to 40 MHz. Heating was attributed to both viscoelastic heating of the bulk material, as well as frictional heating due to the motion of the energetic particles within the binder system.…”

Section: Introductionmentioning

confidence: 99%

Heat generation in an elastic binder system with embedded discrete energetic particles due to high-frequency, periodic mechanical excitation

Mares

Miller

Gunduz

et al. 2014

Journal of Applied Physics

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High-frequency mechanical excitation can induce heating within energetic materials and may lead to advances in explosives detection and defeat. In order to examine the nature of this mechanically induced heating, samples of an elastic binder (Sylgard 184) were embedded with inert and energetic particles placed in a fixed spatial pattern and were subsequently excited with an ultrasonic transducer at discrete frequencies from 100 kHz to 20 MHz. The temperature and velocity responses of the sample surfaces suggest that heating due to frictional effects occurred near the particles at excitation frequencies near the transducer resonance of 215 kHz. An analytical solution involving a heat point source was used to estimate heating rates and temperatures at the particle locations in this frequency region. Heating located near the sample surface at frequencies near and above 1 MHz was attributed to viscoelastic effects related to the surface motion of the samples. At elevated excitation parameters near the transducer resonance frequency, embedded particles of ammonium perchlorate and cyclotetramethylene-tetranitramine were driven to chemical decomposition. V C 2014 AIP Publishing LLC. [http://dx

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“…Dimarogonas and Syrimbeis [12], for example, considered the heat generated in vibrating rectangular plates due to bulk material damping. The related self-heating effect was documented in polymeric materials in the seminal studies by Ratner and Korobov [4,5] and in more recent experiments [13][14][15][16], amongst other places. In the area of polymeric composites, Katunin and Fidali [13,14] conducted experiments using glass fiber-reinforced laminate plates and proposed models of the selfheating effect.…”

Section: Introductionmentioning

confidence: 92%

On the Thermomechanical Response of HTPB Composite Beams Under Near-Resonant Base Excitation

Woods

Miller

Rhoads

2014

Volume 8: 26th Conference on Mechanical Vibration and Noise

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Currently, there is a pressing need to detect and identify explosive materials in both military and civilian settings. While these energetic materials vary widely in both form and composition, many traditional explosives consist of a polymeric binder material with embedded energetic crystals. Interestingly, many polymers exhibit considerable self-heating when subjected to harmonic loading, and the vapor pressures of many explosives exhibit a strong dependence on temperature. In light of these facts, thermomechanics represent an intriguing pathway for the stand-off detection of explosives, as the thermal signatures attributable to motion-induced heating may allow target energetic materials to be distinguished from their more innocuous counterparts. In the present work, the mechanical response of a polymeric particulate composite beam subjected to near-resonant base excitation is modeled using Euler-Bernoulli beam theory. Significant sources of heat generation are identified and used with distributed thermal models to characterize the system’s thermomechanical response. In addition, the results of experiments conducted using a hydroxyl-terminated polybutadiene (HTPB) beam with embedded ammonium chloride (NH4Cl) crystals are presented. The thermal and mechanical responses of the sample are recorded using infrared thermography and scanning laser Doppler vibrometry, and subsequently compared to the work’s analytical findings. By adopting the combined research approach utilized herein, the authors seek to build upon recent work and bridge the considerable gap that exists between theory and experiments in this specific field. To this end, the authors hope that this work will represent an integral step in enhancing the ability to successfully detect explosive materials.

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Thermal and mechanical response of PBX 9501 under contact excitation

Cited by 36 publications

References 17 publications

Ultrasonic hammer produces hot spots in solids

Ultrasonic hammer produces hot spots in solids

Heat generation in an elastic binder system with embedded discrete energetic particles due to high-frequency, periodic mechanical excitation

On the Thermomechanical Response of HTPB Composite Beams Under Near-Resonant Base Excitation

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