Flash X-ray (FXR) is a well known diagnostic technique for many applications. But special tasks give new requirements on the arrangements. Two examples to this are presented here. One task was to measure the asymmetric fragment velocity distribution in the radial directions of "Velocity Enhanced Warheads". This was possible with one flash X-ray, where the X-ray tube was arranged along the charge axis. To find out, what the the true dagonal distances are, the impacts of the radially dispersed fragments on witness plates were used. With the help of the in this way so defined elevation angles the velocities could be well calculated by the displacement distances on the x-ray films. The special test arrangement with the analysis procedure will be presented.
Another task was to measure the momentum distribution of anti-tak mines, lying on the ground or levelled to the ground or 100 mm buried with the help of a double flash X-ray equipment. The transferred momenta could be very well measured. These data are important calibration inputs for numerical models of these very fast events. Test set-ups with achieved results will be presented, too.
The observation of the radial and axial breakthroughs on cylindrical acceptor charges, symmetrically loaded by a shaped charge jet in the axis at one end surface, allows to measure the build up distance from the side and by the radius of the axial breakthroughs. The selected test set up for the observations in the two planes -- parallel to the acceptor charge axis and prependicular to the charge axis on the end surface and the results, achieved with this diagnostic methods, will be described.
Maximum penetration is the goal for good shaped charge designs. To achieve this from the jet, built by the liner collapse process, the jet should have the maximum possible tip velocity for the used liner material and should be extremely straight so that the residual jet portions can arrive at the crater bottom, to achieve a low so-called cut-off velocity. For this purpose the use of the flash X-ray techniques is well known. Great deviations can be easily seen. But the angle deviations should be resolved in minutes in the two axes. For this purpose the author developed the synchro streak technique. The jet is observed in one or two or three different distances with one or two streak cameras, applying the profile streak technique in orthogonal views, so that a two dimensional analysis can be made as a function of time with very high space resolutions. Besides the wanted very accurate measurements of the jet angle deviations, also their surface structure can be observed by strong front illuminations with powerful argon flash bombs. Such synchro streak records have shown smooth jet surfaces in the tip regions, but rougher surfaces in the middle and the rear sections of the jets. The radial crater growing process as a function of time, caused by such extremely fast impactors, can be described with analytical equations. By the optical observation of the radial growth process of the jet at different penetration velocities this analytical theory was proven and confirmed. It is astonishing, that shaped charge research groups and developers are not really knowing and using the possible and relatively easily available optical diagonstic techniques, to find out the limits of the shaped charge jet performances of their designs with the manufacturing tolerances. This paper gives the optical diagnostic potentials and advanced techniques.
In details a test method is described which gives the delay times and buildup distances of the initiation of squeeze cast or plastic bonded high explosive charges. A special test setup arrangement is used to observe the incoming detonation wave of a high explosive train as the donor or initiating charge, then the breakthrough of the detonation wave at the acceptor charge in the axial direction and in the 90° direction. This allows to define the shift of the detonation breakthrough in the longitudinal direction, and the corner turning distance in the transverse direction and the build-up distances in both observed directions.
Flash-X-ray is mostly used in terminal Ballistic studies. The diagnostics of the reaction and detonation behavior of high explosives are the domain of ultra high speed frame and streak cameras. With tricky arrangements of foils, rods, spheres etc. in and around the charge the detonation front or reaction strength can be also very well observed and analyzed with flash-X-rays. Examples of test setups for the diagnostics with FXRs of high explosive charges to measure the time jitter of detonators alone or with explosive trains in multi initiation systems, the change of the detonation velocity of mild detonation cords by different arrangements or by mechanical treatment, the initiability of boosters with mild detonation cords, the internal reaction behavior of high explosive charges at corner turning test, the flow of reaction products, enhanced by embedded foils, reaction strength around a charge in a corner turning arrangement and the reaction behavior in gap test investigations will be shown and highlighted.
The shaped charge jet diagnostic with the so-called synchro- streak-technique (SST) is well described in a number of earlier publications. New insights in the particularized jet behavior have been found with the observation of the jet with 'two' cameras in synchro streak technique in medium and larger distances. The test set-ups with the used two cameras, the gained streak records and their analysis will be described in detail. Some time has to be invested to get a good comparison of the discrete particles recorded at shorter distances or earlier times to the same particles observed at larger distances or later times, a comparison which can be also quickly and well understood by non specialists. These streak records with the corresponding analysis explain the high cut- off velocities of the jets in larger stand-offs and give clear indications on what has to be improved to obtain better qualities.
In so-called cavity charges superfast jets with tip velocities in the range of 25 km/sec are found. Such fast jets are strongly eroding by the perforation of the ambient air. The ablated jet material forms a tube around the jet and is optically protecting the core of the jet itself. With tests, where the jet is elongating in vacuum, this problem does not exist or is drastically reduced. To get enough space resolution, the profile streak technique (PST) was used to obtain the diameter of the stretching jet as a function of the passing time or with respect to its velocity gradient. With this special diagnostic technique the radius of these superfast jets was measured the first time. The used test method with typical results together with the applied evaluation technique will be described.
The detonic people know that the detonation waves need some minimum radius to turn the detonation direction for 90 degrees and much more to come from a forward detonation in a rearward detonation or retonation. Most of the corresponding tests can distinguish between the build-up distance and the necessary minimum radius. The retonation behavior is generally tested with tubular charges where the minimum wall thickness is determined at which a forward detonation converts also into a retonation. A new method with the help of multiple flash gap technique was tried in which the corner turning distance and the retonation behavior or the necessary minimum explosive layer thickness should be defined with 'one' test only.
Precursor air shocks (PAS), which have velocities in excess to the detonation velocities, are generated in slits of high explosive (HE) charges arranged parallel or under an angle of less than 60 degrees to the detonation wave. They are arriving earlier on the end surface of the high explosive charges because the gases expand fastly in radial directions and therefore optically cover the HE surface. Therefore the later arriving detonation front can be observed no longer. But by directly covering the end surface of the HE charge with a transparent medium -- plexiglass -- with slits corresponding to the explosive charge slits, the radial expansion of the PAS's can be delayed so long that the detonation wave profile can be observed on the HE surface. With this 'trick' interesting detonation behavior aspects were found in connection with slits oriented parallel or with small angles to the detonation direction. The used test setups will be described in detail with typical test results and their analyses.
The Corner Turning Distance (CTD) can be measured with different optical diagnostic methods or also with FXR. The CTD's are important values of the detonability of high explosive (HE) charges or indicate at what distance or radius they are able to change a forward detonation in a radial detonation direction. The less sensitive HE's have an increasing problem with this phenomenon. It will be presented an overview of the different, especially the optical diagnostic methods. Their advantages and disadvantages will be illustrated on a number of typical examples. Simple tests which give only the CTD's, and more scientific arrangements allow also to define the so-called dark or dead zones. The CTD values given also good indication for insufficient initiation strength. With this method explosive trains can be also checked very well in their initiation limitations.
Crater growing process in water caused by the penetrating shaped charge jet is recorded simultaneously by frames and profile streak technique. The radial crater growing process in water is recorded the first time with high time and space resolution.
With an appropriate test set up, the Hadland Photonics Ballistic Range Camera (SVR), designed primarily for exterior and terminal ballistics, can also be used very well for studying initiation events and analyzing a variety of detonation phenomena. This paper explains in detail the test set up of one interesting detonic experiment, observed with the Ballistic Range Camera, and the analysis of the results. The ability of the camera to superimpose up to 16 exposures on a single image allowed particularly detailed examination of the detonation propagation, the detonation velocities, the corner turning distance and the nonreacting radial zones.
For the design of barriers for detonation wave shapers in shaped charges, the shock wave attenuation characteristics of different materials or composite arrangements had to be tested. This paper will explain a test configuration for the diagnostic of the shock wave attenuation of homogeneous and sandwiched inert materials, which measures the delay time between the detonation of a doner and an acceptor charge. Applying the double-flash-gap technique, the analyzed pressure levels render possible conclusions about the existence of divergent or convergent detonation waves.
The straightness of the jet is the most challenging problem in shaped charge technology. Hence, the deviation of the jet from the symmetry axis originating from the collapse zone and, additionally, the dispersion velocities generated during the particulation processes are of crucial interest. In order to measure these quantities, one must look perpendicularly to the jet in at least two distances from the jet origin. To achieve this in an expedient and economic way, the author has developed a new electrically driven streak camera. At a writing speed of 1 mm/microsecond(s) the recording time is about 100 microsecond(s) . Such a long continuous recording time is needed to observe the jet as it passes at longer standoffs, and to obtain a highly accurate measurement of the jet straightness in two dimensions. The camera can also be applied in analyzing the 'normal' jet characteristics such as jet velocity distribution, accumulated jet length, accumulated particulization time, discrete particulation times, discrete particulation distances, jet diameter, jet surface characterization etc. By using as many commercially available components as possible the costs can be kept relatively low. By using the coincidence of the slit/slit position a build-in-shutter of 1 ms minimum exposure time is integrated in the camera.
A relatively simple method is explained, which makes it possible to determine the detonation velocity of an infinitely large charge, using a very small size sample. However, this requires additional instrumentation and a simple trick in the design of the sample. A prerequisite for this is that the detonation velocity of a reference high explosive must be known accurately and that this velocity is larger than that of the high explosive to be examined. By observing the front face, the true detonation velocity can then be determined, even with a very small sample size. The theoretical background, test set-up, and execution of the experiments are described below. Beside this special application, sandwiched explosive charges are of general interest in connection with shaped charge design, and generally in the effort to increase the efficiency of explosive energy transmission.
With SST and with its variations in BiSST, OSST, or especially with BiOSST the characteristics of a shaped charge jet, such as tip velocity, length, particulation times and distances, diameters, transverse velocities, tumbling rates, and 3-D jet deviations, can be fully analyzed. All this can be done quantitatively with high accuracy. Observation of the jet surface under bright front illumination provides new insight into its structure under very high strain rates during extreme elongation.
With a bright front illumination of the shaped charge jet it is possible to observe its surface. This technique allows us to check and reassess the jet surface smoothness and provides new insight into the field of the desired material properties, leading to longer particulation times and therefore less disturbed jet particles.
Definitive conclusions about high and low order reactions can be
drawn from individual framing-mode pictures of a rotating mirror
camera record, when both the velocity of the axial propagation of the
reaction along the outer contour and the velocity of radial products
are analyzed at various distances from the plane of initiation. In
this, the intensity of the reaction can be assessed quantitatively
from the radial expansion velocities, even when, for example, a penetrating
shaped charge jet induces a bow wave in the test charge.
A detailed description is given of the test set-up and of the test
results obtained with charges exposed to the impact of a shaped charge
j et.
The simultaneous recording of an event with frames and streak records without parallax (using the same camera) allows streak records to be directly related to strictly spatial events. While the frames give spatial information of the overall event, they often exhibit motion blur due to the limited exposure possible in detonative processes. Nevertheless, they indicate whether the streak record was made in the symmetry plane and whether phase velocities were recorded in the streak records.
The complex pressure profiles or better the shocked volume of shock waves induced in specimens by detonating high explosive arrangements can be measured with a single test if the shock velocities are observed in a large plexiglas-block with both high time and especially also high space resolution. A " large" plexiglass block is necessary that the rarefaction wave from the surfaces is not able to influence the shock profile from the source. The time resolution is generally no problem if an adequate rotating mirror camera is used. High space resolution can also be obtained if a fine grid is used - in this case of 0. 1 mm strips spaced 0. 4 mm apart and glued in the center plan of the plexiglass block. This technique shows that the shock profile for a high explosive charge without any cover plate gives the highest peak pressure which decays quickly. The detonating high explosive charge which is covered with a two millimeter thick disc of copper shows a shock profile which is constant over a certain time. An airgap between the high explosive charge and the measuring plexiglass block always gives a weak shockwave in the beginning. In the case of an uncovered high explosive charge the expansion of the high explosive products gives a fairly smoothly increasing blast or shock wave and in the case of a covered high explosive charge a
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