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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.

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.

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.

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.

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 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.