Search

An original setup is presented to measure the Newtonian Constant of Gravitation G. It is based on the same principle as used in ballistic absolute gravimeters. The differential acceleration of three simultaneously freely falling test masses is measured in order to determine G. In this paper, a description of the experimental setup is presented. A detailed uncertainty budget estimates the relative uncertainty to be of the order of 5.3 x 10-4, however with some improvements a relative uncertainty in G of one part in 104 could be feasible. [ABSTRACT FROM AUTHOR]

The design of optical fiber based heads offering high accuracy and bandwidth for use in VISAR (velocity interferometer system for any reflector) experiments measuring ballistic velocities is described. A new, expanded, model for predicting the distance-dependent collection efficiency of the heads is presented. The model is shown to agree very well with experimental results, both within and outside the 'depth of field'. Various optical heads are demonstrated, to suit different experimental setups and conditions. Designs offering options for high bandwidths, accurate prealignment, and large stand-off distances are discussed. Results from a typical VISAR experiment are presented, verifying that our designs yield high-quality data. [ABSTRACT FROM AUTHOR]

The hydrodynamic operation of the “Forest Flyer” type of explosive launching system for shock physics projectiles was investigated in detail using one and two dimensional continuum dynamics simulations. The simulations were numerically converged and insensitive to uncertainties in the material properties; they reproduced the speed of the projectile and the shape of its rear surface. The most commonly used variant, with an Al alloy case, was predicted to produce a slightly curved projectile, subjected to some shock heating and likely exhibiting some porosity from tensile damage. The curvature is caused by a shock reflected from the case; tensile damage is caused by the interaction of the Taylor wave pressure profile from the detonation wave with the free surface of the projectile. The simulations gave only an indication of tensile damage in the projectile, as damage is not understood well enough for predictions in this loading regime. The flatness can be improved by using a case of lower shock impedance, such as polymethyl methacrylate. High-impedance cases, including Al alloys but with denser materials improving the launching efficiency, can be used if designed according to the physics of oblique shock reflection, which indicates an appropriate case taper for any combination of explosive and case material. The tensile stress induced in the projectile depends on the relative thickness of the explosive, expansion gap, and projectile. The thinner the projectile with respect to the explosive, the smaller the tensile stress. Thus if the explosive is initiated with a plane wave lens, the tensile stress is lower than that for initiation with multiple detonators over a plane. The previous plane wave lens designs did, however, induce a tensile stress close to the spall strength of the projectile. The tensile stress can be reduced by changes in the component thicknesses. Experiments verifying the operation of explosively launched projectiles should attempt to measure porosity induced in the projectile: arrival time measurements are likely to be insensitive to porous regions caused by damaged or recollected material. [ABSTRACT FROM AUTHOR]

A simple and high performance sabot separation technique which is useful even in about 10-m-long supersonic ballistic ranges has been developed. The normal in-flight sabot separation distance is vastly reduced by adding an addition tube with no diaphragm that may cause damage to the projectile. The launch tube of the ballistic range is subdivided to the acceleration, ventilation, and sabot separation sections. In the ventilation section, both the precursor shock wave driven by the sabot when coasting through the acceleration section and the driver gas is vented out to the dump chamber. In the sabot separation section, only the sabot experiences a great dragging pressure imbalance whereas the drag to the projectile is kept negligible. Initially, the whole system except for the driver gas chamber is connected without any diaphragm; the range operation is not accompanied by any high-speed impact among the sabot, diaphragm, and other related solid parts. The experimental environment can be kept clean. The influence of the muzzle blast is eliminated within a reasonably short distance from the muzzle because it delays owing to the ventilation section. Calibration experiments and the demonstration of flow visualization and boom measurement of supersonic flight were conducted using a 25 mm bore, Mach-2 ballistic range. [ABSTRACT FROM AUTHOR]

The design and construction of a 75 mm bore laboratory gas gun capable of velocities up to 500 m s[sup -1] is described. The performance of the gun is compared with the analytical interior ballistics model of Pidduck and Kent [A. E. Seigel, Report No. AGARDograph 91 (1965)]. The gun is constructed for two idealized loading geometries. One is plate impact, in which the loading is in one-dimensional strain, accomplished by impacting plane impactors onto targets aligned to micron tolerances, precisely normal to the impact axis. Another is pressure-shear in which the target and impacting plate are angled, but still aligned to the same tolerances. The system requires flexibility for addressing the problem of reactive targets when design must allow complete detonation of the target (up to 250 g). This has been accomplished and the system approved for use by the appropriate authorities. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]