Papers by Keyword: Hypervelocity Impact

Abstract: The debris clouds produced by hypervelocity impacts on Ti-based metallic glasses (Ti-MGs) and Al-6061-T6 bumper were studied by smoothed particle hydrodynamics (SPH) methods. The change of the vanguard shape, dispersion and ejection angle were also obtained with the same bumper thickness to the projectile-diameter ratio (h/d). For the same h/d valve, the debris cloud of Ti-MGs bumper had a more widely dispersion and ejection angle than with Al-6061-T6 bumper; the vanguard velocity of Ti-MGs bumper was also lower than Al-6061-T6 bumper. Moreover, for the same bumper areal density, the vanguard of the debris cloud in MGs bumper was plane-shaped. This study demonstrates that Ti-MGs exhibit an excellent bumper protection performance, which asset can pave new paths for their further applications.

Abstract: It is an inevitable phenomenon that flash is generated in the process of hypervelocity impact. The research on impact flash is of important significance for assessing the collision between space debris and spacecraft, identifying the material properties on the surface of planet, evaluating the damage of weapon system. A measurement system was built in order to acquire flash spectrum ranging in wavelength from 200 to 1100nm. The relationship between flash intensity and impact velocity was studied. The spectrum consists of line spectrum and continuous spectrum. Line spectrum mainly concentrates in the range of 200-500nm. The spectral lines of the elements were identified. The strong flash happens within 2.2ms after beginning to impact. In addition, the electron temperature of plasma produced in hypervelocity impact is calculated by spectral method, and compared with the temperature measured by Langmuir three probes.

Abstract: All spacecraft in low orbit are subject to hypervelocity impacts by meteoroids and space debris. These impacts can damage spacecraft flight-critical systems, which can in turn lead to catastrophic failure of the spacecraft. The numerical simulations of characteristics of debris cloud produced by an aluminum sphere projectile hypervelocity impact on different material bumpers at normal incidence have been carried out by using the SPH (smoothed particle hydrodynamics) technique. The effects of impact velocity, the ratio t/d of the bumper thickness to the projectile diameter and the bumper materials on the debris cloud characteristics are presented.

Abstract: We investigated the effects of impact velocity on ejecta size when aluminum alloy 2017-T4 spheres with a diameter of 3.2 mm impacted aluminum alloy 6061-T6 targets with a thickness of 30 mm at velocities of 2 to 7 km/s. We used a two-stage light-gas gun at the Institute of Space and Astronautical Science (ISAS)/Japan Aerospace Exploration Agency (JAXA). To examine the scattering angles of the ejecta, the following was placed 50 mm in front of the target: a witness plate (150 mm × 150 mm, 2 mm in thickness) made of copper with a hole of 30 mm. The ejection behaviors of fragments were observed using a high-speed video camera. The size distributions of the ejecta were examined in detail. The cumulative number of ejecta was proportional to the square of the impact velocity; in other words, to the impact energy of the projectiles. An experimental formula was created by curve fitting of the cumulative number distribution of the projected areas to a bilinear exponential distribution model when the aluminum alloy spheres struck the aluminum alloy targets.

Abstract: Shield structure based on ceramic coating on aluminum bumper was designed, and a series of hypervelocity impact tests were practiced with a two-stage light gas gun facility. Impact velocities were varied between1.5km/s and 5.0km/s. The diameter of projectiles were 3.97mm and 6.35mm respectively. The impact angle was 0°. The damage of the ceramic coating on aluminum bumper under hypervelocity impact was studied. It was found that the ceramic coating on aluminum bumper could help enhancing the protection performance of shield to resist hypervelocity impact. The results indicated when the ceramic coating is on the front side of aluminum bumper, it was good for comminuting projectile and weakening the kinetic energy of projectile. For a certain aluminum bumper, existing a critical thickness of ceramic coating in which capability of Whipple shield to resist hypervelocity impact is the best. On this basis, the proposal of the optimum design for ceramic coating on aluminum bumper was made.

Abstract: In the study, a software program named “SUPER CE/SE” is developed for the simulation of hypervelocity impact problems with large deformations, high strain rates and spall fractures. In the software program, an Eulerian method consisting of an improved CE/SE (Space-time Conservation Element and Solution Element Method) scheme is used. A void growth model which takes the Bauschinger Effect (BE) into account and a newly proposed front tracking method are adopted in the simulation. The formation and propagation of a crack is described by a newly developed automatic crack growth algorithm. Numerical simulation of spall fracture in a plate when impacted by a spherical projectile at a velocity of 6.0 km/s is carried out. The numerical results are in qualitative agreement with the corresponding experimental data. It turns out that the BE has obvious influence on the length of the crack and better agreement with the experiment is obtained when the BE is considered. It is also validated that the newly proposed front tracking method is feasible and reliable for representing the cracks in the problems with large deformation and high strain rates. According to those research results, it is proved that the software program SUPER CE/SE is robust and effective in the simulation of hypervelocity impact problems.

Abstract: The Smoothed Particle Hydrodynamics (SPH) method is a very important method to resolve hypervelocity problems and the basic theory of SPH method is introduced here. Then the three dimensional hypervelocity impact problems are simulated by using the model of chair. The results of SPH analysis show that (SPH) method is a numerical calculation method to resolve hypervelocity problems without mesh model but the particle model must be getting to calculate and the program code is less than other method. By analysis the results of the simulation is reasonable and very similar to the test result. It can be concluded that the advantages of SPH demonstrated make it a good and an ideal method to simulate the impact problem and other problems.

Abstract: The spall fracture is a shock wave induced dynamic fracture phenomenon, it’s difficult to capture the features of the spall fracture when traditional finite element method based on continuum mechanics is applied. In this paper, a new and flexible meshless method, material point method, is used to study the spall fracture of metal material in the case of hypervelocity impact. Firstly, a computational process is given in which Johnson-cook plasticity model, Mie-Grüneisen equation of state and several failure models including hydrodynamic tensile failure model, effective plastic strain model and Johnson-cook failure model are considered. Then a 3D simulation of spall fracture of an armco iron target under impact loads by a 2024-T351aluminum projectile is carried out. At last, the numerical results show that the material point method can accurately capture important features of spall fracture such as the arrival times, magnitudes and shapes of both the compressive waves and tensile reflections in the spall region, and it’s proven that material point method is suitable to simulate the spall fracture in engineering applications.

Abstract: In order to study the fragmentation of projectile and ejection of debris clouds caused by hypervelocity impacting mesh bumper, simulation of aluminum sphere projectile hypervelocity normal impacting aluminum mesh bumper was practiced with SPH arithmetic of LS-DYNA soft. The diameter of projectile was 4mm. Impact velocities of aluminum spheres were varied between 2.2km/s and 6.2km/s. The impact angle was 0°. The relationship between the debris clouds characteristic of projectile and the impact position on aluminum mesh bumper was studied. The effect on fragmentation of projectile from different combination mode of aluminum mesh bumper was analyzed. The results showed that the morphologies of the debris cloud varied with the impact position when a projectile impacted the mesh bumper. The debris clouds as palpus was found, and some local kinetic energy concentrated appeared in the debris clouds. Debris clouds distribution was more uniform when projectile impacted wire across point on the mesh bumper. Debris clouds had more diffuse area and less residual kinetic energy when mesh bumper was combined with interleaving mode. Mesh bumper combined with interleaving mode was helpful in enhancing the protection performance of shields.

Abstract: A series of hypervelocity impact tests on stainless steel mesh/aluminum plate multi-shock shield were practiced with a two-stage light gas gun facility. Impact velocity was approximately 4km/s. The diameter of projectiles was 6.4mm. The impact angle was 0°. The fragmentation and dispersal of hypervelocity particle against stainless steel mesh bumper varying with mesh opening size and the wire diameter were investigated. It was found that the mesh wall position, diameter of wire, separation distance arrangement and mesh opening had high influence on the hypervelocity impact characteristic of stainless steel mesh/aluminum plate multi-shock shields. When the stainless steel mesh wall was located in the first wall site of the bumper it did not help comminuting and decelerating projectile. When the stainless steel mesh wall was located in the last wall site of the bumper, it could help dispersing debris clouds, reducing the damage of the rear wall. Optimized design idea of stainless steel mesh/aluminum plate multi-shock shields was suggested.