Donald J. Grosch

A hypervelocity fragment launcher based on an inhibited shaped charge

Abstract A hypervelocity fragment launcher based on an inhibited shaped charge was developed, which launches a 0.5–1.0 g aluminum fragment at 11.2±0.2 km/s . Experimental and computational work performed during its development are presented. The launched fragment is characterized by in-flight flash radiography and impact crater examination.

Experimental impacts above 10 km/s

Abstract In the proceedings of the last symposium, recent work on a technique for launching small projectiles to hypervelocities above 10 km/s using an inhibited shaped charge was presented [1]. In the interim, experiments have been conducted using the inhibited shaped charge to launch aluminum, nickel, and molybdenum projectiles. This paper presents the results of the impact tests, as well as discusses the shaped charge design modifications for the nickel and molybdenum launchers. Radiographs are presented of the impacting projectiles, as are post test photographs of various targets. The data are unique in that they represent low L D projectile impacts into both monolithic blocks and spaced plates at velocities above 10 km/s. The aluminum projectiles are being launched at 11.25±0.20 km/s, the molybdenum projectiles at 11.72±0.10 km/s, and the nickel projectiles at 10.81±0.10 km/s.

Development and optimization of a “micro” two-stage light-gas gun

Abstract This paper details the steps taken to develop and optimize a “micro” two-stage light-gas gun system. The micro gun described in this paper has a 5.56-millimeter (mm) pump tube and a 1.78-mm launch tube. The original gun configuration is presented, followed by a description of our analysis and revision of the gun system. The modifications to the micro gun system and their effect on the performance of the gun are discussed.

Bursting of shielded pressure vessels subject to hypervelocity impact

Abstract During the 30-year lifetime of the Space Station, NASA is concerned that a large piece of orbital debris could strike one of the inhabited or laboratory modules. The modules are basically cylindrical pressure vessels, 4.3 meters in diameter and 9.1 meters long, made of Al 2219-T87. There is a potential for unstable crack growth (“unzipping”) in these pressure vessels if a sufficiently-long crack were formed in the pressure vessel wall. The ragged hole generated when debris strikes an exterior shield and impulsively loads the pressure vessel wall could lead to such a crack. The central concern of this research is quantifying the minimum crack length (critical crack length) to initiate unstable crack growth. This paper reports on a two-part investigation into this problem: 1) fracture experiments and analyses aimed at determining the fracture resistance and critical crack length of the module walls, and 2) examination of impact data to determine the impact conditions that could cause the critical crack length to be exceeded. Al 2219-T87 was found to be a modestly rated sensitive material, exhibiting an increase in both ultimate strength and fracture toughness at high strain rates. The results of the conservative linear elastic fracture mechanics analyses indicate critical cracks at least 22.9 cm in length are required for unzipping (3.17-mm thick wall), and 45.7-cm length (for 4.83-mm thick wall). The dynamic analysis results indicate that the critical crack lengths are even longer, about 48.3 to 61.0 cm in length. Examination of the rather limited experimental database indicates that the dynamic analysis values are more realistic, and that under certain conditions of projectile size, wall stress, and shield design the critical crack length can be exceeded.

Numerical Simulation of Bird Strike Damage on Jet Engine Fan Blade

Aircraft jet engine should be designed to keep the required performance against for the event of foreign object ingestion, such as bird-strike. For the purpose to realize highly efficient and more advanced design of fan blade of jet engine, a numerical simulation technique for bird-strike problem has developed. Good agreement was obtained between simulation results and the soft body impact tests described in this paper. It was also shown that bird-strike problem has to be recognized as a fluid-structure interaction problem, because the impacted bird behaves like fluid and the impact force is highly influenced by the deformation of fan blade.Copyright

A new technique for monitoring inhomogeneous deformation during flyer plate impact

A new and unique experimental configuration was developed and demonstrated to measure the inhomogeneous deformation of heterogeneous materials during flyer plate impact tests. Flyer plate experiments were performed on a granite material with a small scale structure; strain rates ranged from 105 to 107 s−1. A cross section of an impacted target was monitored and photographed during, and immediately following, passage of the shock wave through the material. Up to fourteen images were taken during passage of the shock wave. This was accomplished using an ultra-high speed Imacon camera with very short exposure times; for example, in one experiment the exposure time was 5 nanoseconds with a framing rate of 5 million frames per second. Continuous wave lasers were used as the illumination source. Edge and notch filters were used to lessen the intensity of the impact flash in the image. The photographic data was analyzed using a digital image correlation (DIC) system. These experiments examined inhomogeneous defo...

Evaluation of ballistic events using a Moiré fringe image processing methodology

This paper describes a Moire fringe based image analysis system that was developed to determine the out-of-plane deformation of target plates impacted by high velocity projectiles. Due to the highly dynamic conditions that occur as the results of these impacts, such data are very difficult to acquire and analyze. Nevertheless, they are essential for the evaluation of armor materials designed to minimize behind- armor debris, and to study the fracture effects of very strong yet brittle advanced armor materials. Additionally, the data sought is required for fundamental verification of computational material models meant to simulate failure in ballistic experiments. The major goal for developing such a system was therefore to image and analyze the three- dimensional high-speed deformation, fracturing, and propagation of fractures that leads to the onset of fragmentation of targets during impact. The specific image processing methodologies discussed include noise reduction, automated and assisted Moire fringe finding, and the remapping of two-dimensional fringe patterns into three-dimensionally distorted surfaces. Results of applying the image processing system are also provided and methods for increasing system robustness in the presence of higher levels of noise are also discussed.