High-density Projectiles Research Articles

Experimental study concerning the oblique impact of low- and high-density projectiles on sedimentary rocks

We conducted four sets of impact experiments using sedimentary rock targets and three different kinds of projectiles at a variety of impact angles in order to examine how the density of a projectile affects the dimensions of a crater as the angle of impact decreases, the threshold angle for the formation of elliptical craters, and the threshold angle for the formation of pits. The crater profiles, crater volume, equivalent diameter, length, width, depth, and ellipticity of each set were carefully measured to be used in comparison with small craters that formed on the weak rocky surfaces of planetary bodies. The results indicate that the crater volume, equivalent diameter, width, and depth decrease with the impact angle, while the length of the crater within a set does not decrease monotonically with impact angle. This trend in crater length is consistent with the results of previous studies. Although craters formed at higher impact angles have a central pit, the pit becomes unclear and eventually disappears as the impact angle decreases. A larger threshold angle is required for the formation of pits at slower impact velocity than at higher impact velocity. Our results suggest that the presence of a central pit is indicative of impacts at higher angles and/or higher velocity. The ratio of the volume of craters resulting from oblique impacts to that of craters formed by normal impacts was proportional to the power of the sine of the impact angle. The power index was found to range between 1.46 and 2.20, with an average of 1.57. Comparison of the averaged power index to the power index of the π-group crater scaling rules, it is experimentally suggested that the hypothesis indicating that the vertical velocity component controls crater formation is plausible on a brittle target. The threshold angles for the formation of elliptical craters for three different kind of projectiles were almost consistent with those obtained in previous studies. Our results strongly suggested that the threshold angle for the formation of elliptical craters for high-density impactor, such as iron meteorites, are higher than for rocky impactors. We then obtained a relationship between the threshold angle for the formation of pits and the cratering efficiency. It is revealed that the threshold angle for the formation of pits is greater than the threshold angle for the formation of elliptical craters, when the cratering efficiency is in the range 7–30. A well-developed pit-spall structure in the crater may be used to indicate both, the impact angle and the vertical component of the impact velocity.

Comparison of Crater Behavior of Water Ice by Low and High Density Projectiles under Hypervelocity Impact

Hypervelocity impact tests have been performed on water ice in the velocity range of 3 to 7 km/s, by using low and high density projectiles. The projectile materials included polycarbonate and stainless steel, with diameter of 1.0 mm. The ice targets were solid cylinders at 253K made from pure water. The crater morphology in the solid ice caused by different projectile and different velocity were observed. The crater sizes were measured and compared with previous tests impacted by aluminum projectiles. The results showed that: 1) the crater diameter and crater depth were dominated by different mechanisms, the crater depth was mainly caused by the projectile penetration, while the crater diameter was mainly caused by the ice spallation; 2) the crater depth showed stronger projectile density dependence than crater diameter, while the crater diameter by higher density projectile showed stronger velocity dependence than that by lower density projectile; 3) the crater volume scaled with the impact energy, the crater diameter by high density projectile showed ‘energy scaling’ behavior, while the crater diameter by lower density projectile showed ‘momentum scaling’ behavior.

Influence of Different Types of Guns, Projectiles, and Propellants on Patterns of Injury to the Viscerocranium

Gunshot injuries to the oral and craniomaxillofacial region vary with the type of gun used. Computed tomography (CT) is the standard diagnostic tool for assessing tissue damage in patients with gunshot injuries. Cone-beam computed tomography (CBCT) is a new imaging technique that has recently become available for clinical diagnosis. The objective of this study was to characterize injury patterns with a focus on gun types and identify the imaging modality that is best suited to assessing injuries caused by different gun types. We present the cases of 14 patients who sustained gunshot injuries to the viscerocranium during the past 10 years. The injuries were caused by 8 basic combinations of handguns or long guns with soft lead core projectiles, partial or full metal-jacketed bullets, and different propellants. Diagnosis was based on clinical and radiological findings (including CT and CBCT). We found a direct correlation between the gun/projectile combination on the one hand and the diameter of the wound track, tissue contamination, and tissue destruction on the other. Entrance and exit wounds are indicative of certain gun/projectile combinations. High-density projectiles cause severe artifacts in CT, unlike CBCT, making it difficult to evaluate anatomic structures in close proximity to the projectile. Every gun/projectile combination is associated with a typical pattern of injury. Even in the absence of the offending projectile, it is thus possible to narrow down the likely gun and/or projectile. In the diagnostic imaging of injuries caused by high-density projectiles, CBCT is more suitable than CT.

A debris cloud cratering model

A model is put forth to predict the depth of cratering penetration into a witness-block (WB) that has been loaded by a debris cloud generated from a projectile impact into an uprange bumper-shield (BS). The independent variables are debris cloud spray angle, radius to depth ratio of the WB craters, impact velocity, BS thickness to projectile diameter ratio, and BS/WB separation distance to projectile diameter ratio. The model is valid for impact scenarios where the debris material within the cloud is comprised of mostly solid fragments. Distributions for fragment size, shape, velocity and mass are implicitly combined and incorporated into the model by a single empirical parameter. This parameter is chosen so as to correlate to a large set of cratering depth data for aluminum. This parameter assignment also finds the model to closely match a small set of experiments with molybdenum as the projectile and BS material. The model is also adapted to the scenario of a high density projectile impacting a low density BS. Using the same empirical parameter assignment as for the aluminum and molybdenum cases the model is shown to also produce good results for a steel projectile and polymethyl-methacrylate BS.

Microcraters formed in glass by projectiles of various densities

An experiment was conducted investigating the effect of projectile density on the structure and size of craters in soda lime glass and fused quartz. The projectiles were spheres of polystyrene-divinylbenzene (PS-DVB), aluminum, and iron with velocities between 0.5 and 15 km/sec and diameters between 0.4 and 5 microns. The projectile densities spanned the range expected for primary and secondary particles of micrometer size at the lunar surface, and the velocities spanned the lower range of micrometeoroid velocities and the upper range of secondary projectile velocities. There are changes in crater morphology as the impact velocity increases, and the transitions occur at lower velocities for the projectiles of higher density. The sequence of morphological features of the craters found for PS-DVB impacting soda lime glass for increasing impact velocity, described in a previous work (Mandeville and Vedder, 1971), also occurs in fused quartz and in both targets with the more dense aluminum and iron projectiles. Each transition in morphology occurs at impact velocities generating a certain pressure in the target. High density projectiles require a lower velocity than low-density projectiles to generate a given shock pressure.