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The purpose of this research is to formulate a generic analytical model to assess the phenomena of water ricochet for a conical nose shaped projectile. A theoretical model is analyzed to study the critical angle of conical nose shaped projectile entering in water and is extended for different mediums as normal sand and mercury. Numerical Simulation has been carried out to find the effect of tip angle of the conical nose shaped projectile on the critical angle. Critical angle is defined as that angle of impact of the projectile above which ricochet will occur. This angle is obtained by balancing the momentums acting on the projectile at the time of impact on the basis of Newtonian theory. Major factors affecting critical angle are impact velocity, impact angle, density of the projectile and the target. An attempt has been made to study the effect of longitudinal spin of the projectile on the critical angle.

In order to design hybrid rocket engines, we have developed a numerical prediction approach to the internal ballistics. The key point is its cost performance. Therefore simple but efficient models are required. Fluid phenomenon and thermal conduction phenomenon in a solid fuel should be treated time-dependently, because characteristic times of these phenomena are longer than those of other phenomena. Besides, they are solved with the energy-flux balance equation at the solid fuel surface to determine the regression rate. It is confirmed that numerical evaluation of time- and space-averaged regression rate is the same order of magnitude as that in experiments. However, the factors n in ṙ = aG¯oxn differ between calculations and experiments.

Principal Component Analysis (PCA) has been applied to thru-transmission ultrasound data taken on ceramic armor. PCA will help find and accentuate differences within the tile, making it easier to find differences. First, the thru-transmission ultrasound data was analyzed. As the ultrasound transducer moves along the surface of the tile, the signal from the sound wave is measured as it reaches the receiver, giving a time signal at each tile location. The information from this time signal is dissected into ten equal segments, and the maximum peak is measured within each segment, or gate. This gives ten measurements at each tile location that correspond to tile depth An image can be made for each of the ten gate measurements. PCA was applied to this data for all of the tile samples, and a performance measure was developed from the loading information. A performance measure was developed and tested on six samples from each of the panels. When these performance measures are compared to the results of the ballistics tests, it can be seen that the performance measure correlates well to the penetration velocities found from the ballistics tests.

During the flight of vehicles, their propulsion energy must overcome gravity, to ensure the displacement of air masses on vehicle trajectory, to cover both energy losses from the friction between a solid surface and the air and also the kinetic energy of reflected air masses due to the impact with the flying vehicle. The flight optimization by increasing speed and reducing fuel consumption has directed research in the aerodynamics field. The flying vehicles shapes obtained through studies in the wind tunnel provide the optimization of the impact with the air masses and the airflow along the vehicle. By energy balance studies for vehicles in flight, the author Ioan Rusu directed his research in reducing the energy lost at vehicle impact with air masses. In this respect as compared to classical solutions for building flight vehicles aerodynamic surfaces which reduce the impact and friction with air masses, Ioan Rusu has invented a device which he named free compression tube for rockets, registered with the ...

A simple go/no-go test for body armor panels using pressure-sensitive, dye-indicator film (PSF) has been shown to be statistically effective in revealing subcritical damage to body armor panels. Previous measurements have shown that static indicator levels are accurately reproduced in dynamic loading events. Further impact tests on armor worn by a human resuscitation dummy using instrumented masses with an attached accelerometer and embedded force transducer have been performed and analyzed. New impact tests have shown a reliable correlation between PSF indication (as digitized images) and impact force for a wide range of impactor energies and masses. Numerical evaluation of digital PSF images is presented and correlated with impact parameters. Relationships between impactor mass and energy, and corresponding measured force are shown. We will also report on comparisons between ballistic testing performed on panels damaged under various impact conditions and tests performed on undamaged panels.

Boron Carbide (B4C) is widely used to provide ballistic protection in challenging service environments. This work was carried out to develop non‐destructive testing (NDT) for B4C characterization. Deliberate flaws were introduced within the B4C tiles during manufacturing. An experimental program was undertaken to determine the best method to detect defects in ceramic tiles and material characterization. Ultrasonic characterization of the material was found to be able to detect both density variation and defects within the material.

Decreasing the weight of protective systems, while minimizing the decrease in ballistic performance, is an ongoing goal of the Army. Ceramic materials are currently combined with other materials in these types of structures in order to decrease weight without losing ballistic performance. This includes structures in which the ceramic material is confined in some way and in which the ceramic material is completely encapsulated. Confinement or encapsulation of ceramic material within a structure generally adds complexity and cost. Relatively simple panel specimens fabricated with ceramic tiles on aluminum backings and side confinement using steel were evaluated using nondestructive methods, including x‐ray computed tomography and ultrasonic testing. The nondestructive evaluation results will be discussed and compared, including the detectability and mapping of fabrication features.

A twin Lumonics K922M pulsed TEA CO2 laser system (∼50 ns FWHM spike, with selectable 1.5 or 2.5 μs tail—depending upon laser gas mixture) was employed to experimentally measure the axial impulse behavior of a family of lightcraft engine geometries, using a lightweight ballistic pendulum. Axial impulse performance in both airbreathing and solid ablative rocket (SAR) modes was examined as a function of: a) laser pulse energy (∼12 to 40 Joules); b) pulse duration (∼50 ns spike with 1.5 or 2.5 μs tail); and, c) engine geometry. The four engines under investigation were the Lightcraft Types ♯150, ♯200 and ♯250, and a 11 cm parabolic bell. Lightcraft ♯200 axial CM performance reached 250 N/MW, which is sharply higher than the 120 N/MW previously reported for the engine using long pulse (e.g., 10‐18 μs) CO2 electric discharge lasers.

This study aims to characterize the interaction of explosive blast waves through simulated anatomical models. We have developed physical models and a systematic approach for testing traumatic brain injury (TBI) mechanisms and occurrences. A simplified series of models consisting of spherical PMMA shells housing synthetic gelatins as brain simulants have been utilized. A series of experiments was conducted to compare the sensitivity of the system response to mechanical properties of the simulants under high strain‐rate explosive blasts. Small explosive charges were directed at the models to produce a realistic blast wave in a scaled laboratory test cell setting. Blast profiles were measured and analyzed to compare system response severity. High‐speed shadowgraph imaging captured blast wave interaction with the head model while particle tracking captured internal response for displacement and strain correlation. The results suggest amplification of shock waves inside the head near material interfaces due to...

Digital Speckle Radiography (DSR) is a technique allowing full field displacement maps in a plan within an opaque material to be determined. The displacements are determined by tracking the motions of small sub‐sections of a deforming speckle pattern, produced by seeding an internal layer of lead and taking flash x‐ray images. An improved DSR algorithm is discussed which can improve the often poor contrast in DSR images, such that the mean and variance of the speckle pattern is uniform. This considerably improves the correlation success relative to other similar algorithms for DSR experiments. A series of experiments involving the penetration of granular media by long‐rod projectiles, and the improved correlation achieved using this new algorithm, are discussed.

When a projectile approaches the back surface of a target, complicated mechanics and different failure modes ensue that can lead to perforation. There have been a number of attempts to model these different failure modes, for example models due to Ravid and Bodner [1] and Walker [2]. Of particular interest are analytic models (as opposed to hydrocode models) where the model attempts to explicitly identify relevant failure modes and back surface breakout modes. This paper examines back surface breakout and target failure models with different failure modes to see how they are invoked in specific impact geometries and scenarios. Comparisons are made of thresholds and sensitivities for the different failure modes to gain a greater understanding of their usefulness and applicability. The model results are compared to data to ensure reasonableness of the computations. Good agreement is shown with a relatively simple back‐surface‐strain target failure mode for predicting ballistic limit velocity for large aspect‐ratio projectiles and relatively thick targets as compared to the projectile diameter.

A high‐speed digital camera was used to observe the deflection‐time history of a Kevlar® fabric to bullet impact. It was observed, as others have, that the deflecting fabric has the shape of a pyramid. The average apex angle of the pyramid was calculated from the digital images and was found to be constant with time for the first 50 to 70 microseconds. Using this information, a simple momentum transfer model is shown to capture the velocity‐time history of fabric deflection until ply failure. As expected, once ply failure occurs, the model overpredicts deceleration of the bullet.

Flat, hemispherical and ogive-2 nosed mild steel projectiles (10 mm diameter, 100 mm length) were fired at 200 m s{sup -1} into the end face of cylindrically confined dry sand (100 mm diameter, 150 mm length). Projectiles were tracked through the sand using flash radiography and high speed photography. By seeding a horizontal plane of randomly dispersed lead shot (

Accurate predictions of non‐eroding penetration are becoming a problem of increasing technological importance. Sandia's Zapotec (a coupling of Pronto3D and CTH) has been the code of choice for design purposes, but there have been some concerns expressed about relying on a single code methodology. Consequently, LLNL's ALE3D (which uses a slide line based approach) is currently being investigated for applicability. As a benchmark, we choose to model the penetration experiments of steel projectiles against aluminum targets to examine the differences between the two methodologies.

Operation of a two‐stage implosion‐driven hypervelocity launcher in which the launch tube is imploded behind the projectile is examined. In particular, techniques to generate a high phase velocity of implosion are explored, and the technique of using a variable thickness flyer plate with a constant thickness layer of explosive is selected for further investigation. An analytic model, based on the Gurney analysis for flyer plate acceleration, is developed to determine the thickness profile necessary to deliver the desired phase velocity. Finite element simulations and experimental implementation of this approach results in the correct increase in phase velocity along the launch tube, however, the velocity profile does not generate the desired constant acceleration profile.

This paper evaluates the potential performance of a microwave propelled craft as a future space transportation system. The engine performance is evaluated on the basis of a the thermodynamic Lenoir‐cycle. Different propellants are discussed for the in‐space part of the ascent trajectory. A launch trajectory analysis with parameter variation is performed. Based on the results of the trajectory analysis the recurring launch cost is estimated. The study concludes with the derived margins for the vehicle's airframe design.

We have synthesized several of new energetic complex perchlorates According to the data of derivatographic analysis, the complexes are thermally stable compounds. One of the promising ways of regulating ballistic characteristics of highly filled energetic formulations is the introduction of modifiers of burning. Complex compounds of d‐metals are effective modifiers of the process of burning. Ballistic tests were made in a constant pressure bomb and demonstrated that the prepared compounds are promising modifiers of the burn rate and can be used in the developed formulations of rocket propellants.

We present the results of development of explosive systems for investigating multiple action of solid projectiles upon an obstacle at a moderate impact velocity on the order of 1 km/s. Two types of systems are considered, namely: 1) evacuating shock tube with plane high explosive (HE), 2) ballistic gun with distributed shot of plastic HE. In the first system an acceleration of steel spheres are realized in flux of expanding explosive products. The second system provides the acceleration of a “soft” plastic block with steel spheres having certain mutual orientation. The experiments with these explosive systems testify to higher effectiveness of projectiles penetration into obstacles at multiple impact with a moderate velocity.

The technique of Digital Speckle Radiography (DSR) has been shown to be widely applicable to the field of ballistics through its ability to measure internal displacement fields to a high precision. In a DSR experiment, a flat plane, typically 500 μm thick, of X‐ray opaque filings are introduced into the sample during manufacture. Flash X‐rays can then be used to image the plane, both before and during an impact event, to produce random speckled images on an X‐ray film. Small sub‐regions of the images can be tracked relative to each other using a Digital Speckle Photography (DSP) correlation algorithm. This produces a displacement field within the specimen on the seeded plane. By repeating an experiment with identical specimens, but varying the delay of the X‐ray exposure, a full time history of the impact event can be obtained.

Computational solid mechanics (CSM) for ballistics, as it exists today, does not have predictive capabilities that are comparable to those of computational fluid dynamics (CFD). The most important reason for this is the lack of high quality physical models for the damage and failure processes that occur during high‐speed impact. An approach for modeling impact damage in metals, based on physical modeling of adiabatic shear bands and voids, will be presented. Scaling laws for damage from shear bands have been developed over the past decade from detailed analysis of the thermomechanical processes, and are being adapted for efficient use in large‐scale computations. A similar approach for ductile void growth and spall has also been initiated. This approach is expected to lead to models that are based on the essence of the physics, rather than on fitting of phenomenological models to large databases.

Some of the recent efforts to improve the ballistic performance of lightweight armors utilize functionally graded materials to provide a continuous transition in properties between dissimilar materials. It has been conjectured that the elimination of abrupt acoustic impedance changes may result in beneficial stress wave attenuation. We examine this issue for some idealized one‐dimensional problems in which all materials are linear elastic. Exact solutions are compared with DYNA3D simulations of the same problems.

The new technique of digital speckle X‐ray flash photography (DSXFP), which has been successfully applied to polyester and cement specimens, is being further developed and used to study materials in ballistic situations in a way not previously possible. The technique involves seeding the specimen with a lead layer and then taking flash X‐ray images before and during an impact event. Digital cross‐correlation can then be used to make measurements of the internal displacements occurring throughout the specimen. Using a stereoscopic geometry the out of plane displacements can also be determined and a full 3‐dimensional displacement map constructed. In this paper these two powerful and complementary techniques of flash X‐rays and DSXFP are used to study the ballistic response of a borosilicate sample to produce information that other techniques are unable to provide.

The dynamic behavior of a solution heat‐treated, water‐quenched and aged U‐0.75wt%Ti alloy was studied in planar (disk‐on‐disk) and reverse ballistic (disk‐on‐rod) impact experiments performed with a 25 mm light‐gas gun. The impact velocity ranged from 100 to 500 m/sec. The impacted samples were softly recovered for further metallographic examination. The VISAR records of the sample free surface velocity, obtained in planar impact experiments, were simulated with 1‐D hydrocode for calibrating the parameters of modified Steinberg‐Cochran‐Guinan (SCG) constitutive equation of the alloy. The same SCG equation was employed in 2‐D AUTODYN simulation of the alloy response in the reverse ballistic experiments, with VISAR monitoring of the lateral sample surface velocity. Varying the parameters of the strain‐dependent failure model allows relating the features of the recorded velocity profiles with the results of the examination of the damaged samples.

With the development of plasticity theory in the 1940s and 1950s, the modeling of penetration has become increasingly analytical and accurate. Currently, analytic penetration models are able to accurately predict depths of penetration for simple penetration geometries where the target and projectile are metals. The most accurate models use sophisticated plasticity analysis to obtain target resistances, but they usually end up expressible as relatively simple explicit differential equations. The most promising development in recent years is the centerline momentum balance, and this technique will be reviewed with some discussion of the meaning of terms by way of first principle physics. A recent model that successfully predicts ballistic limits of fabrics will also be discussed. In addition to addressing what is known, the most pressing questions that need to be answered and what is currently known on those problems will be discussed. Questions include: the transition from eroding to rigid penetration; the...

We present a model for the steady-state penetration phase of yawed long rods. The projectile-target interaction is comprised of axial deceleration and erosion due to frontal pressure, and lateral deceleration due to cavity expansion pressure. By solving the resulting ODEs through time-stepping, the evolution of the projectile/crater shape is obtained.

With scientific objectives for Earth observation programs becoming more ambitious and spacecraft becoming more autonomous, the need for innovative technical approaches on the feasibility of achieving and maintaining formations of spacecraft has come to the forefront. The trend to develop small low-cost spacecraft has led many scientists to recognize the advantage of flying several spacecraft in formation to achieve the correlated instrument measurements formerly possible only by flying many instruments on a single large platform. Yet, formation flying imposes additional complications on orbit maintenance, especially when each spacecraft has its own orbit requirements. However, advances in automation and technology proposed by the Goddard Space Flight Center (GSFC) allow more of the burden in maneuver planning and execution to be placed onboard the spacecraft, mitigating some of the associated operational concerns. The purpose of this paper is to present GSFC’s Guidance, Navigation, and Control Center’s (GNCC) algorithm for Formation Flying of the low earth orbiting spacecraft that is part of the New Millennium Program (NMP). This system will be implemented as a close-loop flight code onboard the NMP Earth Orbiter-1 (EO-1) spacecraft. Results of this development can be used to determine the appropriateness of formation flying for a particular case as well as operational impacts. Simulation results using this algorithm integrated in an autonomous ‘fuzzy logic’ control system called AutoCon™ are presented.

It is well known that impact inclination is detrimental to penetration performance for long-rod projectiles into semi-infinite targets. The drop-off in performance, measured as the depth of penetration normalized by the initial projectile length, is generally attributed to interference of the tail of the projectile with the side walls of the penetration cavity. However, little has been done to study the effect of impact inclination on the performance of long rods penetrating finite targets. A reverse ballistic experiment and three-dimensional numerical simulations are used to examine the effect of impact inclination against an oblique plate. In particular, the interaction of the projectile with the plate, to include asymmetric enlargement of the penetration channel and side loading of the projectile, are examined in the simulations, and compared to experimental results.

The loading history for the hypervelocity impact of a long-rod striking a moving flat plate at an oblique angle was analyzed using the EPIC code. The loads were reduced to their axial and lateral components to provide insight into the penetration problem as well as indicate temporal regimes where loading must be considered in the design and analysis of long rod penetrators. Furthermore, the effect of an EPIC input parameter, the erosion strain, used for the numerical treatment of eroding interfaces was assessed with attention focused on the predictions of peak loads, mass loss, and final configuration of the rod.

When a long-rod penetrator impacts a target at a high yaw angle, interference of the penetrator with the sidewall of a crater is the mechanism for the degraded penetration performance. The yawed penetrator is described as a series of cylindrical elements. Using this assumption, the model considers the effective diameters of the penetrator whether or not it interacts with the crater wall and a revised crater profile is calculated with the effective diameters.

We present a numerical method as applied to flows generated by ignition and combustion of reactive solid particles. Strong shock waves are characteristic features of these flows and must be correctly resolved. For configurations that are typical of Interior Ballistics we adopt a two‐phase, two‐dimensional, axially‐symmetry and unsteady mathematical model. Numerical results for test problems are presented.