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  • 11
    Electronic Resource
    Electronic Resource
    Shear strength measurements in a tungsten alloy during shock loading (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 6707-6709 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Lateral stress measurements in a tungsten alloy, in combination with known Hugoniot data, have been used to find the shear strength of this material, and its variation with longitudinal shock stress, up to 14 GPa. Results show that the shear strength increases significantly with increasing stress. Prior to this work, there has been disagreement in the literature on the effect of shock stress on the shear strength of tungsten and its alloys. The present work agrees with the data obtained by Zhou and Clifton [J. Appl. Mech. 64, 487 (1997)] who used pressure shear. However, the range of stresses studied has been greatly extended. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371748
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  • 12
    Electronic Resource
    Electronic Resource
    The effects of target compliance on liquid drop impact (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 533-540 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: When a liquid drop impacts a solid surface, the contact periphery at first expands more quickly than the compression wavefronts in either liquid or solid. The liquid behind the shock envelope is compressed and high pressures of order ρCV result, where ρ is the density of the liquid at ambient pressure, C the shock velocity in the liquid, and V the impact velocity. At a later stage, the shock envelope overtakes the contact periphery and a jetting motion, which releases the high pressures, commences. The magnitude and duration of the high pressures are critical in explaining the damage mechanisms and erosion processes caused by liquid impact. The experiments described in this paper use the two-dimensional gel and photographic techniques developed for visualizing the shocks, recording the onset of jetting, and measuring jet velocities. This particular study is primarily concerned with the effect of target compliance on the early stages of impact. It is shown that the greater the target compliance, the longer the delay before jetting commences. Two critical conditions are shown to be useful in discussing jetting. The first defines when the shock envelope overtakes the contact periphery and liquid can "spall'' into the air gap. The second defines when this spalled liquid appears ahead of the contact periphery as an observable jet. Both these conditions are investigated and the implications of the results for erosion damage are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.343136
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  • 13
    Electronic Resource
    Electronic Resource
    Thermal, fracture, and laser-induced decomposition of pentaerythritol tetranitrate (1986)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 59 (1986), S. 3945-3952 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This paper describes a study of the decomposition of pentaerythritol tetranitrate (PETN) using a high-resolution time-of-flight mass spectrometer. The decomposition was induced by fracturing single crystals and by laser irradiation. In the fracture experiments, the energy input was varied from the lowest level necessary to produce smooth cleavage surfaces to high-energy loading which produced rough conchoidal fracture surfaces. In the laser experiments, a ruby laser was used in both normal and Q-switched modes, and again the energy input was varied. For all the various experiments, the reaction products were analyzed and reaction schemes are proposed. It is shown that low-energy fracture causes decomposition which follows the same reaction pathway as that induced thermally, with initial failure at the RO-NO2 bond. However, high-energy fracture results in the breaking of the C-C bonds. Two reaction pathways were observed with the laser irradiation. The first is the normal thermal process, but evidence was also found for failure at the R-ONO2 bond. The reaction continued for several milliseconds after the end of the laser pulse, suggesting a "partial'' ignition of the explosive. In other experiments, the conditions for laser initiation of PETN in vacuum were investigated. Explosion occurred when Q-switched pulses of 1 J energy were applied to a molten layer of PETN.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.336743
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  • 14
    Electronic Resource
    Electronic Resource
    Anomalous detonation velocities following type II deflagration-to-detonation transitions in pentaerythritol tetranitrate (2002)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 4995-5001 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The detonation velocity following type II deflagration-to-detonation transitions (DDT) has been observed to be markedly different to that which would be expected were the charges directly initiated. In charges of pentaerythritol tetranitrate (PETN) velocities as high as 5.6 mm μs−1 have been observed compared to 3.7 mm μs−1 which is both predicted and measured for the charge were it to be directly initiated. Experiments have also been carried out that attempt to measure the temperature within columns of PETN prior to a type II DDT event. Other experiments and hydrocode simulations have been carried out that attempt to isolate the possible causes of the anomalous detonation velocity and as a result determine what the critical factors that determine the velocity are. These studies have led to a greater understanding not only of the reasons behind the change in detonation velocity, but also of the stages that occur in the build up to type II DDT. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1462415
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  • 15
    Electronic Resource
    Electronic Resource
    The initiation of fine grain pentaerythritol tetranitrate by laser-driven flyer plates (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 65-69 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Charges of pentaerythritol tetranitrate (PETN) were impacted by laser-driven flyer plates launched from substrate backed aluminum films. The flyers were produced by single pulses from a Q-switched Nd:YAG laser. The aluminum flyers were between 3 and 5 μm thick, had diameters of 1 mm, and achieved velocities up to 8 km s−1. The stresses were intense but of only nanosecond duration. This falls into an interesting regime since the shock thickness of a few microns is of the order of typical hot-spot sizes and less than the grain size of conventional explosive powders. Ultrafine PETN (∼1 μm grain size) was readily initiated, whereas conventional, 135 sieve PETN with a grain size of 106 μm was not, although limited reaction was observed in some cases. Environmental scanning electron microscopy was carried out to help elucidate the differences in behavior. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.373625
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  • 16
    Electronic Resource
    Electronic Resource
    A new mechanism for deflagration-to-detonation in porous granular explosives (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 1749-1753 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An investigation has been carried out into the differences between the deflagration-to-detonation (DDT) process as it occurs in low density [∼30% theoretical maximum density (TMD)] columns of conventional grain size (∼180 μm) pentaerythritol tetranitrate (PETN) and in ultrafine PETN with a grain size ∼1 μm. The principle technique for observing the process utilized charges confined within a steel housing fitted with a polycarbonate slit window. This allowed direct recording of the transition using high speed streak photography. The explosive was thermally ignited using a pyrotechnic mixture with low gaseous emission to minimize any prepressurization of the charge. In addition to the photographic records of the events, the outputs of photodiodes along the length of the column were monitored in order to determine the rate at which the reaction proceeds. The results obtained show that the DDT process in the larger grain PETN at low density was similar in structure to the DDT process at higher densities. In contrast a different mechanism leads to detonation in columns composed of the smaller grain size PETN when packed to densities less than 50% TMD. After ignition hot gases propagate along the column both compacting and igniting material as they pass. After the gases have reached the downstream end of the column, the column continues to burn and the pressure and temperature increase. Some time later initiation takes place at a point along the burning column, and detonation waves propagate in both directions from this point. The detonation waves propagate from the initiation point at speeds that would normally be associated with material compacted to around 60% TMD. The process appears to be in effect a deflagration-to-localized thermal explosion detonation transition. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.370957
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  • 17
    Electronic Resource
    Electronic Resource
    The use of liquid jets to simulate angled drop impact (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 7111-7118 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The liquid jet impact technique has been used extensively for the quantitative study of rain impact. Most of this work has been for normal impact. Although some angled impact studies have been pursued using jets, these have been purely of a qualitative nature. This paper develops the theory of angled drop impact. This allows the establishment of a method of correlating between angled drop and jet impact and obtaining "equivalent drop'' curves for jet impact. The correlation is also applied to normal impact. For normal impact it is shown that the previously published equivalent drop curves need to be modified especially at low velocities. The results for both normal and angled impact are discussed with reference to the details of the jet profile, and it is shown that angled jets may be considered as having an average equivalent drop size. The theory of angled impact also explains the shape of damage marks produced by impact and why the amount of damage decreases so rapidly with increasing angle.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349793
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  • 18
    Electronic Resource
    Electronic Resource
    High-speed photography of surface geometry effects in liquid/solid impact (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 1015-1021 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Recent theoretical studies of liquid/solid impact, in particular the geometric wave theory of Lesser and Field, have emphasized the importance of the detailed geometry in the contact area. In parallel with the theoretical work, we have developed a two-dimensional technique using gels for impact and shock studies. A combination of high-speed photography and schlieren optics allows the shocks in the liquid and solid, if it is transparent, to be visualized, as well as important processes, such as jetting, to be recorded. This paper describes the gel technique and gives results for a range of surface geometries for collision velocities of a few hundred meters per second. The relevance to damage initiation in liquid/solid impact problems, such as rain erosion, steam turbine blade erosion, and cavitation, are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.340000
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  • 19
    Electronic Resource
    Electronic Resource
    Influence of oxygen pressure on laser ablation of YBa2Cu3O7−x (1990)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 57 (1990), S. 922-924 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The luminous ablation plume formed by laser irradiation of the superconductor YBa2Cu3O7−x has been investigated by high-speed framing photography. The pressure of the background oxygen gas was found to influence significantly the velocity distribution of ejected products. Pressures above 0.25 mbar resulted in the formation of shock waves and instabilities on the shock front.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.104268
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  • 20
    Electronic Resource
    Electronic Resource
    The spall strength of alumina ceramics (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 84 (1998), S. 734-738 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The response to plate impact loading of three aluminas with varying glass content and porosity has been investigated. Spall strengths have been shown to be dependent on the amplitude and duration of the compression pulse which precedes the tensile loading, but insensitive to the rate of release. Some tensile strength is measured in impacts where the Hugoniot elastic limit has been exceeded. The effect of the material microstructure on the dynamic tensile strength has also been studied. Low porosity aluminas with many microstructural irregularities were found to possess the lowest spall strengths. Experimental values compare well with those predicted by an energy balance theory developed by Grady [J. Mech. Phys. Solids 36, 353 (1988)]. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.368130
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