Caliber Gun Research Articles

Development of Technologies to Apply Refractory Metals to Large Caliber Gun Bores

To increase the service life of large caliber naval guns, several technologies were evaluated by the Office of Naval Research for their ability to apply a refractory metal bore surface that would survive the severe thermal, chemical and mechanical environment. These technologies were evaluated using gun firing tests designed to produce a bore surface condition that replicated the intended application. Tests were conducted in 45 mm, 76 mm and 155 mm scale with rapid fire conditions evaluated at both 76 mm and 155 mm scale. Where possible the results have been compared to a chrome plated sample subjected to the same firing conditions.

M2 Machine Gun Barrel Wear with SLAP Ammunition

The M2 machine gun has a Stellite-lined barrel. When Saboted-Light-Armor-Penetrator (SLAP) ammunition is fired in M2 barrels, the bore often constricts below the minimum diameter in less than 2,500 rounds. The requirement is 10,000 rounds. When fired with ball ammunition, the M2 barrel exceeds that requirement. Although SLAP ammunition is not widely used, solving the wear issue with SLAP may improve the barrel life with ball ammunition. The following work is presented: a literature search, an analysis of the wear phenomenon and manufacturing process, as well as recommendations to improve M2 barrel life. Brief mention will be made of prototype small caliber gun barrels being fabricated and tested. Previous work and testing conducted herein find that the bore constriction is most likely caused by inadequate shrink fit during the barrel assembly process. That is, test results find some correlation between barrels with low round count and non-conforming barrel assembly.

Impact of Intensity of Residual Stress Field Upon Reyielding and Re-Autofrettage of an Autofrettaged Thick Cylinder

Re-autofrettage has been identified as a significant, cost-effective method to achieve higher reyield pressure (RYP) and/or weight reduction in large caliber gun tubes. For a given overstrain, residual stress profiles for hydraulic and swage autofrettage may differ significantly in their intensity. The simplest representation of this “intensity” effect is the magnitude of the bending moment “locked in” via the residual hoop stress. Hill’s analytical, plane strain, Von Mises analysis predicts a larger “locked-in” moment than does the equivalent open-end condition. By assuming a range of stress-field intensities (f) scaling from 1.0 to 1.4 times that were produced by open-end hydraulic autofrettage, it was possible to assess reyield behavior following initial autofrettage via a generic numerical study. In cases where Bauschinger effect is absent, reyield initiates at the original elastic–plastic interface. This includes the ideal Hill distribution. When Bauschinger effect is present, reyield for f≤1.1 initiates at the bore and after further pressurization at the original elastic–plastic interface within two zones. For f≥1.2, the reverse is the case, with initial yield at the original elastic–plastic interface and subsequently at the bore. RYP increases with increasing f up to f = 1.175 and then decreases significantly. This loss of RYP may be mitigated by hydraulic re-autofrettage. At f = 1.0 re-autofrettage increases RYP by 4%. At f = 1.4, RYP is increased by 19%. There are modest increases in safe maximum pressure (SMP) as a result of re-autofrettage. RYP closely approaching re-autofrettage pressure is achievable for f≥1.3. Within this range, re-autofrettage offers a significant benefit. Re-autofrettage also produces beneficial effects via increased bore hoop compressive stress, this increase varying from 20% for f = 1% to 0% for f = 1.4. Such increased compression will benefit fatigue lifetime for fatigue cracks initiating at the bore. Conversely, tensile outside diameter (OD) hoop stress increases, with increasing f, by a maximum of 6%.

My Addiction: The Artificial Kidney, The Rise and Fall of Dialysis

My Addiction: The Artificial Kidney, The Rise and Fall of Dialysis

Characterizations of gun barrel vibrations of during firing based on shock response analysis and short-time Fourier transform

The behavior of shock vibration for a medium caliber gun barrel was experimentally investigated and then, numerical modal analysis, a signal processing technique as well shock response analysis were carried out en route to the detailed analyses. This approach was initiated by identifying mode frequencies from the numerical model and thus the frequencies were clarified using the periodogram together with the spectrogram based on the time frequency analysis. A shock response analysis was employed to draw more physical interpretations regarding the barrel behaviors due to firing shock. In this paper, therefore, the overall process of shock vibration analysis was demonstrated for analyzing the shock behavior of the gun barrel.

마찰스프링의 주퇴복좌장치 적용성 연구

The conventional medium and large caliber gun, in general, utilize the hydro-pneumatic recoil mechanism to control the firing impulse and to return to the battery position. However, this kind of mechanism may cause the problems like the leakages and the property changes in oil and gas due to the temperature variations between low and high temperatures. Accordingly, the friction spring mechanism has recently been researched as an alternative system. The friction spring mechanism consists of a set of closed inner and outer rings with the concentric tapered contact surfaces assembled in the columnar form, and can only be used under the compression load. When the spring column is axially loaded, the tapered surfaces become overlapped, causing the outer rings to expand while the inner rings are being contracted in diameter allowing an axial displacement. Because of friction between tapered contact surfaces, much higher spring stiffness is obtained on the stroke at the increase in load than the stroke at the decrease. In this paper, the dynamic equations regarding the friction spring system and the design approach have been investigated. It is also tried for a dynamic model representing the recoil motion and the friction spring forces. And the model has been proved from firing test using a gun system with friction springs. All the results show that the recoil mechanism using friction springs can substitute for the classic hydro-pneumatic recoil system.

Experiments on the Combustion Characteristics of Deterrent-Coated Propellants and Their Application in Traveling Charge Propulsion

The combustion characteristics of deterrent-coated propellants and their application in a 105 mm caliber gun are investigated experimentally. The mixture of deterrent-coated and conventional single base propellant particles are fired in a 100 ml closed bomb with loading densities of 0.1 g/cm3 and 0.2 g/cm3, respectively. The measured pressure time profiles indicate that the deterrent can retard the combustion of coated propellants, and the delays are related to the pressure and the thickness of the deterrent. The optimized deterrent-coated propellants are attached to the tailfin of a 105 mm caliber armor piercing projectile (APP) as traveling charge, and fired in a 105 mm caliber gun. The firing results indicate that the traveling charge of deterrent-coated propellants can improve the muzzle velocity of projectiles by 2.8% and 4.2% under maximum pressure of 330 Mpa and 400 Mpa, respectively. The pressure time curves measured in the chamber indicate that pressure plateau effects can be expected by the combustion delay of deterrent-coated propellants.

Artileria cetăţii Timişoara la 1716 / The Guns Of The Fortress Of Timişoara (Temesvar) in 1716

On October 13, 1716, the ottoman garrison of Timişoara (Temesvar) surrendered after a 43 days lasting siege to fi eldmarshall prince Eugene of Savoy, commander in chief of the Habsburg army. According to the terms of capitulation, Mustafa pasha, the last governor (beylerbey) of Timişoara, was forced to hand over all the guns, shells and gunpowder located in the fortress. Until October 26, prince Eugene’s offi cers have made a full inventory-list (kept today in Vienna, at the Kriegsarchiv, and published by us) of the captured Ottoman artillery material. On this basis, we are now in position to rebuild the image of the Ottoman artillery at Timişoara in the eve of the siege from September-October 1716, as well as the losses suff ered during the 43 days of the battle.On August 31, being surrounded, the ottoman fortress of Timişoara – the largest in the region after the fortress of Belgrade – was defended by 156 guns: 123 bronze fi eldguns (with calibers ranging from a quarter pound to 48 pounds/weight of the shells), 16 iron fi eldguns (with calibers ranging from half a pound to 70 pounds), 9 bronze morters (with calibers ranging from 60 to l00 pounds) end 8 howitzers (with calibers ranging from one pound to 48 pounds). During the siege, 62 guns (41%) were completely destroyed, while 92 pieces (59%) survived, being used by the Imperials to defend Timi şoara. 120 guns (76,9% from the originally 156 were small caliber pieces (from a quarter pound to 12 pounds), 23 (14,8%) were medium caliber guns (from 15 to 36 pounds) and the remaining 13 were heavy caliber pieces (from 48 to 100 pounds). 84 guns of Timişoara (53,8%) were made in Ottoman gunneries, while the remaining 72 (46,2%) were German, Austrian and Transylvanian pieces from the 16th–17th centuries, seized by the Ottoman army during the battles with the Habsburgic troops. While 41 ottoman guns (48,9%) were completely des troyed during the siege, the remaining 43 (51,1%) have been kept by the Imperials to defend Timişoara. As for the occidental guns, only 5 pieces were prior to 1552, when the fortress of Timişoara was taken after an Ottoman siege. Other 8 guns were from the second half of the 16th century, among them 2 Transylvanian pieces, most probably seized by the Ottomans during the unsuccesful siege of Timişoara by prince Sigismund Bathory in 1597. Several pieces are marked with the name of the German, Austrian or Italian gunmaster (e.g. from Nürnberg, Augsburg, Pressburg, Salzburg, Cremona or Milan) and the date of their manufacture. & e 35 German and Austrian guns from the 17th century – most of them from the last two decades – landed in Timişoara as a result of the military clashes between the Habsburgs and the Ottomanic Porte, especially during the long war from 1683 to 1699. At the same time, we have to point out, that the Ottoman fortress of Timişoara was very well provided with shells and gunpowder. After its surrender, the imperial army captures here 13.022 diff erent shells, 2.823 centennials (about 158 metric tons) of gunpowder and about 2.000 centennials (about 112 metric tons) of leadplates.

Study of the Control Platform of Robot Ammunition Loading System

Aimed at work characteristics and work environment of auto loading manipulator for large caliber gun, its control system based on double CPU is designed. Then the paper expounds the components of the entire control system and corresponding principle. The control system can test control algorithm and motion trajedy plan in order to develop new control strategy and short development time.

Research on a Novel Capacitive Pressure Sensor to Measure Chamber Pressures of Different Caliber Artilleries

The research and development on a novel capacitive pressure sensor with an elastic pressure-sensitive element are presented in this paper. As a coaxial cylinder capacitor converter, it uses a circuit cylinder as its stationary anode and the piezo gauge's shell as its moveable cathode with the electrode distance of 0.5 mm. The device's principle and structure are given, and its mechanical characteristics are theoretically simulated by using the finite element software ANSYS. The read-out circuitry was developed. Various physical properties were experimentally tested. Results show that its capacitance is approximately linear to the subjected pressure. Its sensitivity is 0.0099 pF/Mpa, pressure measuring rang is 0-600 Mpa, By using the sensor's shell as its elastic sensitive element, its volume is reduced and its applications are increased, thus it can be used to measure the chamber pressures of various different caliber guns. In addition, its lower cost is helpful to promoting its applications.

Abrasion Failure Lives Simulation and Prediction of Key Parts for Breech Mechanism Based on Virtual Prototype

Breech mechanism is the key and important device to improve reliability and maintenance for large caliber guns. It’s major fault mode is grain abrasion caused by dry sliding friction. There is no feasible and practical technologies to simulate and predict the abrasion failure life of key parts for breech mechanism. A new simulation and prediction method is firstly put forward in this paper. Based on Pro/E and ADAMS, the virtual prototype of breech mechanism of semiautomatic vertical sliding-wedge type is established. To validate its precision and effectivity, qualitative and quantitative verification method are adopted to check the virtual prototype of breech mechanism. Virtual prototype produces key parts’ load spectrums and failure theresholds. Dry sliding friction and abrasion experiment provides abrasion rules of typical materials. Finial simulation and prediction results are given as abrasion thresholds and operating items, which provide sufficient references for breech mechanism’s maintenance and safeguard.

Transient Thermal Analyses of Midwall Cooling and External Cooling Methods for a Gun Barrel

Liquid cooling methods are often used for thermal management of a large caliber gun barrel. In this work, transient thermal analyses of midwall-cooled and externally cooled gun barrels were performed. At first, a novel simulation scheme was developed for the computation of the gun barrel temperature history (temperature variation over time), and its experimental validation was performed. In the computational scheme an internal ballistics code, GUNTEMP8.EXE, was developed to simulate the total heat transfer per cycle for the given ammunition parameters. Subsequently, a finite element (FE) model of the barrel was developed in ANSYS 11.0. Heat transfer to the barrel was approximated by an exponentially decaying heat flux. The FE model was solved to compute for barrel temperature history. Simulations were performed for a burst of 9 cycles, and the results were found to agree with the experimental measurements. Subsequently, the simulation scheme was extended to analyze a burst of 40 cycles at 10 shots per minute (spm). Three cases were investigated as follows: (1) a naturally cooled gun barrel, (2) a gun barrel with midwall cooling channels, and (3) an externally cooled gun barrel. Natural cooling was found insufficient to prevent cook-off, whereas midwall and external cooling methods were found to eliminate any possibility of it. In the context of a self-propelled howitzer, a midwall-cooled gun barrel connected to an engine cooling system was also analyzed.

Study of Confined Pyrotechnic Compositions for Medium/Large Calibre Gun Igniter Applications

AbstractWith the continued shift towards more insensitive munitions and the subsequent development of low vulnerability propellants, the study of novel gun igniters is playing a significant role in the design of future direct and in‐direct fire charge systems. Previously, concepts such as electrothermal plasma ignition have offered high performance ignition solutions. However, using current technology they lack practical, in‐service applicability and will be difficult to incorporate into near future combat systems at a low cost.

Review of thermo-mechanical cracking and wear mechanisms in large caliber guns

Thermo-mechanical cracking has become a critical wear mechanism in modern large caliber guns, due to operational increases in severity of heating at the gun bore in order to increase gun performance. The chromium coating typically used in guns often cracks after one firing, as do tantalum coatings and ceramic liners being considered for future guns. Once small segments of coating are surrounded by cracks, rapid erosion failure is likely. In prior studies to address this problem, models have described the depth and spacing of thermal cracks that develop in bore coatings and identified the mechanism of final separation of a cracked segment of coating. The models have used finite difference calculations of near-bore temperatures and elevated temperature material properties to calculate the thermal expansion stresses which cause both the initial cracking and the final separation of a cracked segment of bore material. The current work will review prior and recent observed damage and the models developed to describe the damage, and then extend the models to a wider range of gun firing conditions and materials from recent tests. Included will be [i] recent firing damage in tantalum coated steel liners in 120 mm inner diameter guns, [ii] additional recent gun-combustion simulation of firing damage in a SiAlON bulk ceramic, and [iii] extension of thermo-mechanical and fracture models showing effects of transient cannon heating and different coating materials on the near-bore temperatures and stresses that control both initial crack formation and final segment separation.

High-Density Infrared Cladding of Ta on Steel

The addition of tantalum to the inside diameter of a gun barrel would reduce erosion during firing of medium and large caliber guns. In this work, chemical vapor deposited (CVD) Ta was bonded to A723 Steel. High-density infrared (HDI) heating was employed to bond Ta to steel at 1440°C while maintaining bulk steel temperatures below the 357°C threshold for retaining beneficial compressive stresses (autofrettage). Through-thickness temperature evolution modeling was performed. Metallographic evaluation of claddings is reported. Characterization of the interface showed that metallurgical bonding occurred while keeping bulk temperatures low.

Second Special Issue on Pressure Vessels Technology Applied to Gun Tubes

The previous open conference with a focus on large caliber gun tube design took place in Oxford, England, in 2002; this gave rise to the August 2003 special issue of JPVT. A second Oxford conference, GT 2005, was held in April 2005; papers from that conference are included in this special issue. The 21st century will require rapid reaction, mobility, and technological effectiveness. This implies weight reduction and more extreme firing environments, including operating pressures, temperatures, and chemistry. In these respects the 30 months between the conferences have produced some significant developments.By design, a large caliber gun routinely operates closer to its fatigue envelope than virtually any other device. The lifetime of a gun tube is limited by bore damage and by fatigue crack growth, frequently mitigated by advantageous autofrettage residual stresses. The maximum firing pressure is selected to limit plastic behavior. A keynote paper reviews the development of these concepts.Fatigue lifetime depends crucially upon near-bore thermal damage arising from initial firings. The thermo-mechanical basis for early craze cracking and subsequent loss of liner material has moved from conjecture to general acceptance. A second keynote paper provides an overview of this crucial development. In other papers, coating-substrate mechanics and alternative coating materials are critically examined. Ceramic liners represent an alternative to traditional coating methods, but raise significant challenges—recent work, part of a major project, is reported herein. The drive for reduced weight and improved portability has resulted in significant numerical and experimental investigation of external carbon fiber wrapping; extensive work is reported in detail.Bauschinger effect, involving the significant nonlinear reverse-loading behavior of pressure vessel steels, reduces the potential benefits of autofrettage; this effect is now incorporated in all realistic analyses. This behavior, unique to each candidate steel, is being fully characterized and made available for input in standard numerical analyses. Other features, including biaxiality effects, are being quantified. Such materials data is, in turn, being used in multi-parameter analysis and optimization. Several papers address one or more of these issues.The GT 2005 conference was organized by the Defence College of Management and Technology, Cranfield University at the Defence Academy, UK. It was sponsored by the U.S. Army European Research Office, the U.S. Army RDECOM–ARDEC–Benét Laboratories, ASME Pressure Vessels and Piping Division, Denel SA, BAE Systems, KMT Waterjet Systems, United Defense, Reheinmetall, and the Institution of Mechanical Engineers, UK. We extend special thanks to all the authors and reviewers, to Dr. M. Schmidt, Professor J. Hetherington, Dr. A. Hameed, and Betsy-Jane Lawton who created a successful and enjoyable conference, and to Professor O. Widera and Ms. J. Bulgrin who made this special journal issue possible.

Hydraulic Testing of Ordnance Components

This paper describes a range of hydraulic fatigue and pressure tests carried out on gun barrels and ordnance components in support of weapons research and development programs. Cyclic testing of representative sections of large caliber guns has been routinely carried out to determine safe fatigue life for operational use. Ultrasonic techniques have been developed for mapping multiple cracks within the gun barrels by which periodic examinations of barrels during testing have been used to build up histories of crack initiation and growth. In relatively unworn barrels multiple cracks, initiated along each rifling groove, are shown to form in an extremely stable array that can grow to several millimeters depth, in agreement with calculated stress intensity factors, before one crack accelerates to dominate final failure. The development of localized erosion from extensive firing is shown to significantly affect the subsequent hydraulic fatigue cycling by generation of only one or two cracks as well as the prior removal of heavily prestressed bore material. Tests on fume extractor sections of barrels show that cracking initiates in the jet holes and only grows to the bore at late stages. Introduction of different levels of autofrettage acts to bias the radial location of the cracks. An extensive experimental program of work has been carried out in support of design studies on mid-wall cooled gun barrels exploring a number of different configurations for construction of compound tubes and the results of numerical simulations of the assembly process have been compared with strain gauge measurements during the experimental procedure on scale tubes. Subsequent hydraulic cycling was used to determine the fatigue implications of the processing route.

Electroplated and Plasma Enhanced Magnetron Sputtered Ta and Cr Coatings for High Temperature and High Pressure Operation

AbstractFor A723 steel large caliber gun barrel applications, high pressure (∼700MPa), rapid cyclic heating-cooling (∼1250°C), and aggressive propellant gases (CO, CO2, H2O, H2, N2, NH3, CH4, H2S etc) operational environment can cause severe wear and erosion damages to the bore, reducing the service life of the component. Refractory bore coatings can help protect the steel bore to extend service life. Cr electroplating process is currently being widely used in industry and in the military, but toxic wastes from the process are difficult and expensive to dispose. Plasma enhanced magnetron sputtering techniques are being developed for potential replacement of the Cr electroplating process. In this work, we compared A723 steel specimens coated with electroplated Cr and plasma enhanced magnetron sputtered Ta and Cr coatings. The specimens were subjected to analytical testing, including scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, metallography; and adhesion testing, including groove test, a pulsed laser heat test to simulate cyclic thermal environment of the bore, and actual firing test. Steel samples electroplated with HC (high contraction) Cr showed extensive pre-deposition cracks, it also showed cohesive failures under groove adhesion test. When subjected to cyclic high pressure and temperature operation, gas-metal interactions led the as-deposited cracks to grow wider and new cracks to develop, allowing hot pressurized propellant gases to penetrate the cracks and erode the steel substrate. Plasma enhanced sputtered Ta and Cr coatings on steel were harder and denser compared to conventional magnetron sputtered coatings. Under groove testing, they showed no cracks, no cohesive and no adhesive failures. When subjected to cyclic pulsed laser heating simulation at 1490°K, thick sputtered Ta showed no crack, no delamination, and no failures. A heat affected zone was observed in steel, which was caused by tempered to untempered martensite conversion. Our data also showed that Ta sputtered in Ar consisted of minimum interface meta-stable tetragonal Ta fingers, which converted to bcc Ta in the heat affected zone; Ta sputtered in Kr consisted of 100% stable bcc Ta under similar experimental conditions.

Gun Barrel Erosion—Comparison of Conventional and LOVA Gun Propellants

The research department Energetic Materials within TNO Defence, Security and Safety is involved in the development and (safety and insensitive munitions) testing of conventional (nitro cellulose based) and thermoplastic elastomer (TPE) based gun propellants. Recently our testing capabilities have been extended with vented vessel tests in order to investigate whether or not newly developed (low vulnerability (LOVA)) gun propellants or propellant formulations perform better in erosion tests. At the moment we have two vented vessel tests available, making it possible to determine the extent of erosion from a relatively low loading density to one comparable to a large caliber gun (maximum allowable pressures from 20 to 400MPa). Test pieces of various materials have been used and a number of LOVA and conventional gun propellants have been tested. From the results of these experiments the wear and wear rate have been determined. The erosion dependency on propellant properties like impetus, flame temperature, and combustion gas composition has been determined. Furthermore, an internal ballistics code has been adapted to model the pressure and temperature development in a vented vessel. The results are compared with the experimental results. This model will be described in short and the results presented.

Consideration of the energy transfer mechanisms involved in SPETC ignition systems

Solid propellant electrothermal-chemical (SPETC) gun concepts have evolved over the past decade. A common difficulty experienced by many of the "large-scale" applications of SPETC technology has been the excessive electrical energy and power requirements needed to produce significant performance benefits. However, one aspect of SPETC gun technology that has attracted a lot of interest is in the area of plasma ignition due to its lower power requirements. It has been shown by various groups that plasma ignition offers benefits over a conventional gunpowder ignition system at large scale. High-energy electrical discharges previously used for ignition can potentially lead to adverse internal ballistics. Effort has recently been directed at reducing the ignition energy stimulus with the result that electrical discharge energies of a few tens of kilojoules are now routinely used to ignite large caliber gun system propellant charges. This not only gives improved internal ballistics but also reduces the cost, size, and complexity of SPETC gun components. An understanding of the energy transfer mechanisms involved during the ignition phase, which allows the electrical energy to be transferred to the surface of propellants, is central to reducing the electrical energy requirements, and these mechanisms are the subject of this paper. There is some evidence for radiative energy transfer being the dominant transfer mechanism for some higher power plasma igniters. However, with low power density and low energy ignition, the radiant flux is negligible in the timescale under consideration, suggesting that radiation is not the dominant process. Supporting experimental evidence from measurements of the radiant flux incident upon the propellant grain surface is offered. These measurements have been performed with the use of embedded optical fibers in translucent propellant formulations. The light collected by these fibers is input to an absolutely calibrated time-resolved spectrograph. A new hypothesis is put forward, which proposes that the energy transfer mechanism for low-power SPETC ignition is dominated by a process of metallic vapor deposition. Modeling and experimental results are presented, which support this hypothesis.