Search

A laboratory gun that uses compressed gas as its propellant was designed and tested for the study of small projectiles traveling in soils with initial velocities ranging from 50 to 200 m/s. The gun employed the use of air or helium with an electrically triggered, pneumatically piloted, solenoid valve. The triggering system was designed to provide remote activation. A photo gate speedometer was utilized to measure the exit velocity of each projectile. Details of the electro-pneumatic control system are presented in this paper along with the design of the gun assembly and its subsystems. The effects of different design parameters, including muzzle length, projectile mass, propellant type, and volume of compressed gas utilized, on projectile velocity were investigated. Statistical analysis of the gun performance is presented. The gun is currently being used to visualize the fundamental physics of rapid earth penetration in soils, using transparent soils.

With more than 1 trillion artificial objects smaller than 1 μm in low and geostationary Earth orbit, space assets are subject to the constant threat of space debris impact. These collisions occur at hypervelocity or speeds greater than 3 km/s. In order to characterize material behavior under this extreme event as well as study next-generation materials for space exploration, this paper presents a unique two-stage light-gas gun capable of replicating hypervelocity impacts. While a limited number of these types of facilities exist, they typically are extremely large and can be costly and dangerous to operate. The design presented in this paper is novel in two distinct ways. First, it does not use a form of combustion in the first stage. The projectile is accelerated from a pressure differential using air and inert gases (or purely inert gases), firing a projectile in a nominal range of 1–4 km/s. Second, the design is modular in that the first stage sits on a track sled and can be pulled back and used in itself to study lower speed impacts without any further modifications, with the first stage piston as the impactor. The modularity of the instrument allows the ability to investigate three orders of magnitude of impact velocities or between 101 and 103 m/s in a single, relatively small, cost effective instrument.

This study evaluates the energy absorption, perforation and damage evolution created by cylindrical projectile of different nose geometries in woven roving mat/epoxy laminates with 0.45� orientation. A series of ballistic impact tests have been carried out on the laminate with projectile nose geometries representing hemispherical, conical, and conical with round nose and truncated tip. A gas gun projectile launcher set-up was employed to impact the target at different speeds. The damage pattern, perforation mechanism and ballistic limit for each type of projectiles have been studied. Truncated-nose projectile shows the highest ballistic limit while sharp-nose shows the lowest. A quasi-static punch test was carried out on targets with projectiles of above-mentioned nose geometries to assess the damage evolution at a constant strain rate. The maximum load required to cause perforation during punch test was noted for hemispherical-nose projectile. An in-depth layerwise analysis was carried out to analyse the damage in each layer. Copyright � 2008 Taylor & Francis.

A research program was funded by the European space agency (ESA) to improve and optimize the shields used to protect the manned elements of the international space station (ISS) against impacts of micro-meteoroids and orbital debris. After a review of existing shielding systems and after a series of light gas gun (LGG) experiments to screen interesting new materials and configurations, the research focused on shields with a metallic outer bumper, an intermediate stuffing and an inner metallic wall (representing the pressure shell of a manned spacecraft). Additional LGG experiments were performed on several configurations, with bumpers containing aluminum foam or made from titanium and aluminum super-alloys and with several combinations of stuffing materials. The comparison of the test results showed that ceramic cloth (Nextel) plus aramid fabric (both 2D and 2.5D Kevlar weaving) used as intermediate bumper gave a good protection compared to the overall area density requested. Configurations with by-layered aluminum foam bumpers (sandwich panels with asymmetric Al face sheets and a core made from Al foam) and Kevlar stuffing showed excellent resistance to normal impacts at about 6.5 km/s. However, the influence of material properties varying from batch to batch and threshold phenomena made ranking among the tested options rather difficult. The test campaign showed that it was rather difficult to improve over the already good ballistic performances of the debris shields developed by Alenia Spazio for the ISS manned elements. The by-layered Al-foam bumper and Kevlar stuffing configuration was selected for additional tests, including low velocity and oblique impacts, to develop ballistic limit curves.

There has long been a need to understand the impact response of explosive materials, and continual improvements result from the design of careful, well-instrumented experiments. This article summarizes details of the design and construction of a laboratory facility capable of launching projectiles at explosive targets at velocities up to 1500 m s−1. There are two types of experiment that are required. In the first, a gun launches a plate of great planarity at an equally flat target. This geometry is known as plate impact and a target loaded in this manner experiences a state of one-dimensional strain. This loading is accomplished by launching plane impactors onto targets aligned to micron tolerances, normal to the impact axis to less than 0.5 mrad of tilt. In the second, it is required to attain the ability to recover impacted explosive targets that have been loaded in one-dimensional strain for subsequent microstructural assessment. The development of this capability will be described in a subsequent pub...

An improved procedure for modeling the operation of a light-gas gun is proposed. The motion of working bodies in both the firing chamber and the light-gas chamber is studied within the framework of the mechanics of heterogeneous media. The problem of barrel heating taking into account its melting and removal of thermal ablation products into the medium inside the bore is solved in a coupled formulation. Heat and mass transfer and friction on the barrel surface are calculated using empirical dependences. The deformable piston is considered compressible and elastoviscoplastic. Allowance is made for the presence of a clearance between the lateral surface of the piston and the barrel bore walls and the associated gas flow between the firing and the light-gas chamber. Calculation results are given.

A new gas gun technique has been developed in which a small mass fragment is impacted in a precise orientation by a thin metal disk and then recovered. The metal disk is placed inside a hollow sabot that also contains a miniature soft-recovery chamber. After impact, the sabot with the fragment inside is recovered in rags. The fragment will be found either in front of the impactor disk or behind it in the soft-recovery chamber, depending upon whether the disk was perforated. This technique can be used to determine accurate ballistic-limit velocity measurements for fragments with masses less than 0.6 gm. Thirty-six experiments have been performed using this technique for masses in the 0.2–0.6 gm range. Results are presented for several experiments.

Research into the high velocity impact of materials has necessitated the setting up of a new facility at the Royal Military College of Science. A light-gas gun and flash x-ray system were acquired to meet the research objectives. In this article, the light-gas gun and auxiliary equipment are described. Modifications were made to the facility to ensure the safety of personnel during a gas gun and flash x-ray firing. An analysis was carried out to select operating parameters within the maximum safe loading condition of the gas gun. The work met the safety and operational objectives, and suggestions for future work are made.

In recent years, great strides have been made regarding the identification of the dominant loads that cause beam type vibrations of cannons during ballistic operation. These motions infringe upon shot accuracy because at projectile disengagement, the muzzle's kinematic state may compromise the projectile's intended flight path. This is particularly relevant to coil gun loading, which, unlike gas launch, applies the recoil load to the muzzle end of the barrel instead of the breech. This effectively places the barrel in a state of columnar compression during the launch cycle that may exacerbate structural vibrations known as gun "whip".

The dual objective of developing the present ballistic model is to predict an accurate force-time history in a monolithic thick plate due to penetration by a projectile, and to analytically describe the physical phenomena that occur during a penetration experiment in conjunction with measuring the physical parameters. The analytical model developed considers the evaluation, and prediction of the following quantities: (a) shape and size of the cavity, (b) residual strength of the target, (c) depth of penetration in the target, (d) residual length of the projectile, (e) pressure distribution along the cavity wall and (f) force-time history for the penetration event.

The Sandia Hypervelocity Launcher (HVL) uses impact techniques on a two-stage light-gas gun to launch flier plates to velocities in excess of 10 km/s. An important problem in designing successful third stage techniques for impact launching fliers to such velocities is detailed understanding of the interior ballistic performance of the third stage. This is crucial for preventing melt and fracture of the flier plates during the extraordinary accelerations that they undergo (accelerations on the order of 10{sup 9} g are typical on the HVL). We seek to optimize HVL launch conditions in order to achieve two major goals: first, to maximize the potential launch velocity for a given flier, and second, to allow different flier configurations. One tool that we can apply in studying HVL performance is the use of multi-dimensional wave propagation codes. We have used such codes, particularly the Sandia Eulerian code CTH, to study a variety of interior ballistics issues related to gun performance and launcher development for almost ten years. Recently this work has culminated in a major contribution to HVL design, namely the capability to launch ``chunk`` fliers. `Me initial phases of design development were solely devoted to CTH computations that studied potential designs, identifiedmore » problems, and posed possible solutions for launching chunk fliers on the HVL. Our computations sufficiently narrowed the design space to the point that systematic experimental progress was possible. Our first experiment resulted in the successful launch of an intact 0.33 gram titanium alloy chunk flier to a velocity of 10.2 km/s. The thickness to diameter ratio of this flier was approximately 0.5.« less

Herein, we study the technique of improving the gun performance by installing a diaphragm in the pump tube of the gun. A CFD study is carried out for the 0.28 in. gun in the Hypervelocity Free Flight Radiation (HFF RAD) range at the NASA Ames Research Center. The normal, full-length pump tube is studied as well as two pump tubes of reduced length (approximately 75% and approximately 33% of the normal length). Significant improvements in performance are calculated to be gained for the reduced length pump tubes upon the addition of the diaphragm. These improvements are identified as reductions in maximum pressures in the pump tube and at the projectile base of approximately 20%, while maintaining the projectile muzzle velocity or as increases in muzzle velocity of approximately 0.5 km/sec while not increasing the maximum pressures in the gun. Also, it is found that both guns with reduced pump tube length (with diaphragms) could maintain the performance of gun with the full length pump tube without diaphragms, whereas the guns with reduced pump tube lengths without diaphragms could not. A five-shot experimental investigation of the pump tube diaphragm technique is carried out for the gun with a pump tube length of 75% normal. The CFD predictions of increased muzzle velocity are borne out by the experimental data. Modest, but useful muzzle velocity increases (2.5 - 6%) are obtained upon the installation of a diaphragm, compared to a benchmark shot without a diaphragm.

We developed a compact two-stage light-gas gun and optimized several operating parameters for aiming at velocities higher than 9 km/s. A firing test achieved a velocity of 6.2 km/s using helium as driver gas with a projectile weighing 0.6 g and a piston weighing 430 g. In the case of firing tests using hydrogen, a velocity of 8.1 km/s was obtained under the same condition. Moreover, it was found that higher velocities could be achieved by using a lighter piston to increase piston velocities, and that the efficiency of acceleration strongly depended on the initial gas pressure for each piston. Finally, a projectile velocity of 8.9 km/s was achieved using a piston weighing 290 g.

Hypervelocity impact experiments that reproduce on-orbit collisions between micrometeoroids or orbital debris and space structures are commonly performed by means of propellant-driven two-stage light-gas guns. Such devices accelerate projectiles using the thrust of a light propellant gas that is compressed to high pressure and temperature by a piston running in a pump tube. Though these guns have the unique capability of accelerating particles up to 9 km/s, many components of the gun must be checked and/or substituted after each shot making test sessions long and expensive. In order to have a lot of and many different types of hypervelocity impact data, the Center of Studies and activities for Space CISAS “G. Colombo” of Padua University developed a high-shot-frequency two-stage light-gas gun that can increase the shot repetition rate of standard facilities by a factor of 5 or more and at the same time reduce the shot cost by a factor of 2 or more. This is made possible through the use of special mechanical and diagnostic solutions that were designed to operate the gun for more than 50 shots in sequence without having to carry out maintenance operations. This article presents the design and operation of the CISAS two-stage light-gas gun damping system, which is one of the subsystems that makes it possible to achieve high-shot frequency. The damping system is in charge of controlling the piston oscillations in the pump tube, making it possible for the piston to withstand more than 100 shots without any damage. In particular, the damping system avoids piston strikes onto the gun head at the end of each compression stroke and allows the piston to be positioned at the base of the pump tube after each shot. The sensitivity of the piston oscillations to the damping operations and main subsystem design parameters were identified using numerical simulations, carried out according to a model that describes every working phase of the gun. Moreover, in this paper, the technical solutions for the damping system implementation are presented and the numerical predictions are compared with experimental results. For the CISAS high-shot-frequency gas gun, an efficient damping system proved to be a fundamental requirement to reliably accelerate 100 mg projectiles above 5 km/s and 70 mg projectiles at 5.5 km/s with a shot frequency of 10 shots per day at least, including the time needed for replacing the target and pumping down the target vacuum chamber.

The Lawrence Livermore National Laboratory (LLNL) Joint Actinide Shock Physics Experimental Research (JASPER) Facility is being developed at the Nevada Test Site (NTS) to conduct shock physics experiments on special nuclear material and other actinide materials. JASPER will use a two-stage, light-gas gun to shoot projectiles at actinide targets. Projectile velocities will range from 1 to 8 km/s, inducing pressures in the target material up to 6 Mbar. The JASPER gas gun has been designed to match the critical dimensions of the two-stage, light-gas gun in Building 341 of LLNL. The goal in copying the LLNL gun design is to take advantage of the extensive ballistics database that exists and to minimize the effort spent on gun characterization in the initial facility start-up. A siting study conducted by an inter-Laboratory team identified Able Site in Area 27 of the NTS as the best location for the JASPER gas gun. Able Site consists of three major buildings that had previously been used to support the nuclear test program. In April 1999, Able Site was decommissioned as a Nuclear Explosive Assembly Facility and turned back to the DOE for other uses. Construction and facility modifications at Able Site to support the JASPER project started in April 1999 and were completed in September 1999. The gas gun and the secondary confinement chamber (SCC) were installed in early 2000. During the year, all facility and operational systems were brought on line. Initial system integration demonstrations were completed in September 2000. The facility is anticipated to be operational by August 2001, and the expected life cycle for the facility is 10 years. LLNL Nevada Experiments and Operations (N) Program has established a Management Prestart Review (MPR) team to determine the readiness of the JASPER personnel and facilities to initiate surrogate-material experiments. The review coincides with the completion of authorization-basis documents and physical subsystems, which have undergone appropriate formal engineering design reviews. This MPR will affirm the quality of those reviews, their findings/resolutions, and will look most closely at systems integration requirements and demonstrations that will have undergone technical acceptance reviews before the formal MPR action. Closure of MPR findings will finalize requirements for a DOE/NV Real Estate/Operations Permit (REOP) for surrogate-material experiments. Upon completion of that experiment series and the establishment of capabilities for incorporating SNM into future experiments, the team will convene again as part of the process of authorizing those activities.

Non-invasive detection methods for tracking gun-launched projectiles are important not only for assessment of gun performance but are also essential for timing a variety of diagnostics, for example, to investigate plate-impact events for shock compression experiments. Measurement of the time of passage of a projectile moving inside of the gun barrel can be achieved by detection of the transient hoop strain induced in the barrel of a light-gas gun by the passage of the projectile using external, barrel surface-mounted optical fiber-Bragg grating strain gauges. Optical fiber-Bragg gratings have been implemented and their response characterized on single-stage and two-stage light gas guns routinely used for dynamic experimentation at Los Alamos National Laboratory. Two approaches, using either broadband or narrowband illumination, were used to monitor changes in the Bragg wavelength of the fiber-Bragg gratings. The second approach, using narrowband laser illumination, offered the highest sensitivity. The feasibility of using these techniques to generate early, pre-event signals useful for triggering high-latency diagnostics was demonstrated.

At projectile velocities exceeding 2000 m/s ablation phenomena due to the heating by air friction may influence flight and impact behavior. Direct in-bore temperature measurements during the flight could clearly improve the theoretical modeling of the heat transfer to hypervelocity projectiles, but the temperature signals must be transmitted from the projectile to the ground station. Since the projectiles are submitted to heavy accelerations, batteries cannot be used as power supply. Therefore, at EMI a low energy telemetry concept is under investigation according to the following principle. At the projectile base a radio frequency reflector with variable reflection coefficient is installed. The reflection coefficient is controlled by an on-board local oscillator, the frequency of which is modulated by the measured signal, e.g., of a temperature sensor. The projectile base is illuminated by an unmodulated fixed frequency ground based radio frequency transmitter, and the signal reflected at the projectile base is picked up by a ground based receiver. The received signal contains the measured signal, shifted by the Doppler frequency, and the Doppler frequency itself. Since controlling the reflection factor of the projectile base only consumes a very low energy, the on-board power supply during the flight phase can be realized by a simple previously charged capacitor. Several telemetry test projectiles of caliber 30 mm have been developed and fired at successively high velocities presently reaching 1850 m/s by the aid of a light gas gun. The actual state of the work and the first results are presented.

For continuous recording of projectile motion in a gas gun, a new method, “inline holographic velocimetry”, is proposed and demonstrated. The inline hologram pattern of a wire is recorded by a streak camera via a mirror, which ismovingbetween the wire and the recording plane. The mirror is glued onto the nose of an accelerating projectile. The projectile motion can be obtained precisely by analyzing the fringe spacings which gradually become narrower with increasing displacement. It was found that the projectile acceleration is almost constant except in the early stage.

A new microvelocity sensor unit was developed to measure the instantaneous velocity of a high velocity impactor during the penetration process. The concept of this device is based on the induced current generated in a coil due to the passage of a magnet. A special digital circuit was designed to yield a spatial resolution of better than 0.05 in. by eliminating the problem of signal overlap. The precise time delays obtained from these signals can be used to determine the slowing down or energy loss of a high‐velocity projectile. The details of this sensor unit will be described and its resolution will be demonstrated. A light gas gun was used to propel aluminum projectiles to velocities up to 320 m/s. Energy loss of these high‐velocity projectiles in composites reinforced with polyethylene, polyester, and graphite fabrics as well as pure Kevlar fabric was measured using this system. Results show that this microvelocity sensor is capable of identifying various energy‐loss processes during the impact of high‐velocity projectiles.

A program was initiated to design, build and evaluate the performance of a two-stage light gas gun, utilizing hydrogen gas, for use as an injector to an electromagnetic railgun. This effort is part of a project to develop a hypervelocity electromagnetic launcher for equation-of-state studies (HELEOS). The specific design features that enhance compatibility of the injector with the railgun, including a slip-joint between the injector launch tube and the coupling to the railgun, are described. The operational capabilites for using all major projectile velocity measuring techniques, such as in-bore pressure gauges, laser and CW (continuous wave) X-ray interrupt techniques, flash X-ray, and continuous in-bore velocity measurements using VISAR interferometry, are discussed. An internal ballistics code for optimizing gun performance has been utilized to interpret performance data of the gun. >

A theoretical and experimental study was made to determine where a fixed length, constant diameter tube should be divided so that when one portion of the tube was used as a gun barrel and the remaining portion was used as a driver, the maximum projectile muzzle velocity would be obtained for a particular driver gas and initial projectile acceleration. Studies were made of several gas gun configurations, of 4-in. (10-cm) inside diameter and 100-ft (30- m) length, for muzzle velocities greater than 500 ft/s (150 m/s). Calculations were made by using the Lagrange theory for very low Mach numbers; the constant diameter, infinite reservoir theory for very high initial accelerations; and the Pidduck-Kent theory for other regimes. Experimental results and theoretical predictions are compared for several gun divisions, helium and nitrogen drivers, and initial accelerations from 200 to 5000 g. For improved gun utilization, gun configurations are suggested to reduce exit gas pressure, to reduce the quantity of driver gas required, and to ease operation and improve (statistical) utilization of the gun without unduly affecting muzzle velocity. Although the results obtained are specific to the Harry Diamond Laboratories 4-in. gas gun, computer programs are included that may be applied to other gun geometries.

A new single-stage, high-pressure, stainless steel, light-gas gun 30 ft long with a 1 3/8-in. bore has been designed and built at DOFL. This gun has driven a 6-gm mass at velocities above 5000 fps. With alterations made to heat the driver section, it is expected to give velocities of over 8000 fps and make possible impact shock pressures of more than 1-megabar. A comparison of the measured and computed projectile velocities at room temperature as well as higher temperatures is included.

Variable-resistance strain gages were used to study the operating characteristics of a light-gas gun. Gages were cemented on the outer surface of the gun at several locations, in order to determine chamber pressure, piston velocity, and pressures in the central breech. The high-pressure transition section deformed plastically in most rounds, and a method is suggested for estimating maximum pressures from strain-time records. Results are given for various helium pressures and powder charges.

Techniques were developed to launch ultralightweight models (i.e., densities on the order of 1 lb/3 cu. ft.) from a two-stage light-gas gun. To date, spheres and cones have been launched with some success. The purpose of the development was to determine whether useful aerodynamic data (e.g., sphere drag) could be obtained in a short aeroballistic range at pressures on the order of 0.01 mm Hg. A number of spheres were launched in support of this effort, some at pressures as low as 0.03 mm Hg. There is good agreement between these measurements of sphere drag coefficient and those produced in low-density wind tunnels. The application of this technique to a longer range having a lower pressure capability, say, 0.001 mm Hg, would permit measurements to be made in the near-free-molecule flow regime.