Search

In this work a series of experiments were carried out in which right-circular cylinders were launched into sand targets at velocities ranging from 70 to 150 m/s. The projectiles were launched along a view window in order to record the penetration event with high-speed photography. Stress measurements of the transmitted wave forms were simultaneously collected from a piezoelectric load cells buried in the sand. A particle image velocimetry (PIV) technique, which extracted information from the photographic images, was used to resolve transmitted wave profiles. A two wave structure was observed. The first wave, a compaction wave, moves at the bulk sound speed of the sand. The second is an attached fracture wave which is stationary relative to the projectile. Together these experiments further our understanding of high-speed granular penetration events. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Digital Speckle Radiography (DSR), a technique allowing measurement of the full field displacement maps in a plane within an opaque material, is used to follow the temporal progression of a long-rod (100 mm long, 10 mm diameter) penetrating a granular sample at a variety of rates. Quasi-static rates of 1.5 mm/min are achieved using an Instron machine, 5 m/s is achieved using a drop-weight and velocities between 10 and 200 m/s are achieved using a light gas gun. These experiments are carried out using a series of time delayed flash x-ray images analysed with an optimised Digital Image Cross Correlation algorithm (DICC). The subsequent data sheds considerable light on the response of granular materials to penetration at a variety of rates. Particularly, a large difference in the response of the material between quasi-static and dynamic rates is observed. [ABSTRACT FROM AUTHOR]

The Johnson-Holmquist ceramic material model has been calibrated and successfully applied to numerically simulate ballistic events using the Lagrangian code EPIC. While the majority of the constants are “physics” based, two of the constants for the failed material response are calibrated using ballistic experiments conducted on a confined cylindrical ceramic target. The maximum strength of the failed ceramic is calibrated by matching the penetration velocity. The second refers to the equivalent plastic strain at failure under constant pressure and is calibrated using the dwell time. Use of these two constants in the CTH Eulerian hydrocode does not predict the ballistic response. This difference may be due to the phenomenological nature of the model and the different numerical schemes used by the codes. This paper determines the aforementioned material constants for SiC suitable for simulating ballistic events using CTH. [ABSTRACT FROM AUTHOR]

Analysis of experimental data using theoretical models reveals that a very small portion of a shaped charge jet particle’s kinetic energy shocking the air in front of it can couple convectively into the particle’s leading surface to soften an already hot material enough to justify hydrodynamic modeling of the air cratering process. [ABSTRACT FROM AUTHOR]

The performance of behaviour of brittle materials depends upon discrete deformation mechanisms operating during the loading process. The critical mechanisms determining the behaviour of armour ceramics have not been isolated using traditional ballistics. It has recently become possible to measure strength histories in materials under shock. The data gained for the failed strength of the armour are shown to relate directly to the penetration measured into tiles. Further the material can be loaded and recovered for post-mortem examination. Failure is by micro-fracture that is a function of the defects and then cracking activated by plasticity mechanisms within the grains and failure at grain boundaries in the amorphous intergranular phase. Thus it is the shock-induced plastic yielding of grains at the impact face that determines the later time penetration through the tile. [ABSTRACT FROM AUTHOR]

Constitutive models for brittle materials such as glass can be very complex as they are dependent on strains, strain rates, pressures, temperatures, damage and other parameters. There may also be significant (pressure-dependent) strength after failure such that the constitutive response is much different for intact material and failed material. A large number of laboratory tests is required to develop a comprehensive constitutive model. Another approach is to develop simple models by using penetration-velocity data obtained from ballistic experiments. Here various functional forms of simple models (with a limited number of constants) can be used to (computationally) match the penetration velocity over a range of impact velocities. This allows for the determination of the most important parameters and it provides an approximation of the stresses that occur during penetration. This article presents several simple computational models for borosilicate glass, including single-state models and dual-state models (that include an intact strength and a failed strength). [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]