Search

A series of plate impact experiments was performed using the single stage light gas gun facility at the Cavendish Laboratory, Cambridge University to determine the dynamic tensile, or spall strength of a hypabyssal kimberlite and a siltstone. Two distinct impact configurations were employed, over a range of impact velocities up to 185 m/s. VISAR and manganin gauges were used to monitor the spalling of the material. Thicker targets were found to be less suited for spall measurements as the signal appeared to be degraded by the increased amount of material traversed before reaching the measuring plane. A comparison with a theoretical scheme relating the spall strength to the Hugoniot elastic limit is performed, and while the agreement is not perfect it is of the same order of magnitude. [ABSTRACT FROM AUTHOR]

A series of plate impact experiments was performed using the single stage light gas gun facility at the Cavendish Laboratory, Cambridge University to determine the principal Hugoniot curves of a hypabyssal kimberlite and a siltstone. A reverse impact configuration was employed, over a range of impact velocities 244–927 m/s. VISAR was the main diagnostic and sample geometry allowed for release characteristics to be studied. The release measurements show a significant deviation from the Hugoniot at higher initial shock pressures, though this does not correspond specifically to the HEL. Combined with other data previously reported the resulting Hugoniots are compared to various static data and a good correlation is shown with elastic impedance. [ABSTRACT FROM AUTHOR]

A series of plate impact experiments was performed to determine the principal Hugoniot curves of geological materials. The experiments were carried out using the plate impact facility at the Cavendish Laboratory, Cambridge University. By means of conventional impacts, over a range of impact velocities 217–1038 m/s, the Hugoniot of a quartz feldspathic gneiss and an amphibolite have been obtained. Manganin stress gauges were used as the main diagnostic tool. The Hugoniots show that the materials are either behaving elastically in the range of interest, or that the elastic limit of the materials are not visible due to there being no significant change in slope at the HEL. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Plate impact experiments have been performed on the igneous diamond-bearing matrix kimberlite. Longitudinal and lateral stresses were measured in the uniaxial strain regime using manganin stress gauges. The shock Hugoniot of the kimberlite has been characterized at axial stresses between 1 and 9 GPa. The kimberlite has a low impedance response when compared with similar data for other geological materials. The data indicate that the rock behaves inelastically above shock stresses of 1 GPa. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

The sensitivity of energetic materials can be tested under various stimuli, such as low velocity impact in a drop-weight, static electric discharge or friction. Gap testing uses an explosive loading as the stimulus. The shock pulse is moderated by a layer placed between the loading charge and a column of the energetic material of interest. This study shows how, with careful attention to the production of the column, the test can be made sensitive to very small changes in the gap thickness of <0.04 mm of polymethylmethacrylate (PMMA). In these tests there is little crossover. This is highlighted by a series of experiments on the secondary explosive PETN with 180 μm grain size compared to samples with sub-micron grain size. A parallel series of experiments using polyvinylidenedifluoride (PVDF) gauges directly measures the level of stimulus experienced by the energetic material. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

An extensive study has been carried out into the relationships between the particle size of a charge, the density to which it is packed, the presence of inert additives and the sensitivity of the charge to different initiating shocks. The critical parameters for two different shock regimes have been found. The long duration shocks are provided by a commercial detonator and the short duration shocks are imparted using laser-driven flyer plates. It has been shown that the order of sensitivity of charges to different shock regimes varies. In particular, ultrafine materials have been shown to be relatively insensitive to long duration low pressure shocks and sensitive to short duration high pressure shocks. The materials that have been studied include HNS, RDX and PETN. [ABSTRACT FROM AUTHOR]

An investigation into the shock sensitivity of hexanitrostilbene (HNS) has been carried out. A Q-switched Nd:YAG laser was used to launch miniature flyer plates from substrate-backed aluminium films. The impact produces a shock with duration of the order of 1 ns and pressure of the order of 10 GPa. The explosive samples were pressed into PMMA cylinders to 65-78 % theoretical maximum density. The threshold laser pulse energy required to produce a flyer with sufficient velocity to cause detonation was found. A high-speed camera was used to record the entire event. Initial curvature of the streak record, for impacts just below the detonation threshold, showed that reaction started inside the column. This feature was not seen in a previous study. It was found that conventional HNS, with a mean particle size of approximately 25 µm, could not be detonated while fine grained HNS (sub-micron particle size) would detonate. [ABSTRACT FROM AUTHOR]

A series of plate impact experiments on cement paste (grout) has been performed to assess the dynamic strength of this material. Lateral stresses have been directly measured by means of embedded manganin stress gauges. In combination with longitudinal stresses, measured previously [1], these results have been used to obtain shear strength under shock loading. Results indicate that the material is behaving in an inelastic manner with the shear strength increasing with increasing pressure. [ABSTRACT FROM AUTHOR]

In-material longitudinal and lateral stress histories in three dense, silica-based glasses were directly measured by embedded manganin stress gauges during plate impact experiments. Lateral stress profiles in all of the materials show evidence of failure fronts that behave in a similar manner to those observed in open-structured glasses. The measured stress histories were used to calculate the deviatoric responses and results indicate that ahead of the failure front the shear stress increases linearly along the estimated elastic response. Behind the failure front, however, the shear stress appears to first decrease and then increase as the pressure increases, contrary to a previous interpretation [1]. [ABSTRACT FROM AUTHOR]

A series of plate impact experiments has been performed to determine the shock loading behaviour of cement paste (grout) with water to cement ratio of 0.35 by weight and no aggregates. Hugoniot stress data were collected by means of embedded manganin gauges up to 5 GPa. Results are then compared to those obtained in previous studies on concrete varied on aggregate size using a plate reverberation technique and velocity interferometry. Results indicate that the average loading of cement and concrete are comparable. In addition, the in-material gauge technique has the advantage of estimating the cement Hugoniot directly and provides a measurement of the rise times, which were found to be inversely related to impact stresses. [ABSTRACT FROM AUTHOR]