High Velocity Impact Dynamics Zukas Pdf ((BETTER)) Free
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High speed impacts are complex phenomena influenced by various parameters. To predict the structural damage caused by a high speed impact, it is necessary to investigate the effect of various impact conditions, such as the incident angle, the nose shape and diameter of the projectile, and the material and thickness of the plate, on the behavior of the structures. Although the projectile incident angle considerably influences the behavior of steel structures, studies on this subject have been limited. Thus, this study investigates the effect of the projectile incident angle on the deformation of the steel plate and the penetration behavior of the projectile. It was found that the projectile incident angle significantly influences the plate deformation and the angle, velocity, and kinetic energy of the projectile.
Hypervelocity impacts generate extreme pressure and shock waves in impacted targets that undergo severe localized deformation within a few microseconds. These impact experiments pose unique challenges in terms of obtaining accurate measurements. Similarly, simulating these experiments is not straightforward. This study proposed an approach to experimentally measure the velocity of the back surface of an A36 steel plate impacted by a projectile. All experiments used a combination of a two-stage light-gas gun and the photonic Doppler velocimetry (PDV) technique. The experimental data were used to benchmark and verify computational studies. Two different finite-element methods were used to simulate the experiments: Lagrangian-based smooth particle hydrodynamics (SPH) and Eulerian-based hydrocode. Both codes used the Johnson-Cook material model and the Mie-Grüneisen equation of state. Experiments and simulations were compared based on the physical damage area and the back surface velocity. The results of this study showed that the proposed simulation approaches could be used to reduce the need for expensive experiments.
Hypervelocity impact events are ubiquitous in many areas, including micrometeoroid collision with spacecraft, projectile impacts, and when modeling effects of explosives on structures. Consequently, researchers have been studying various aspects of this problem for several decades. A common technique to study hypervelocity impact in laboratory settings is the two-stage light-gas gun [1, 2], which can accelerate a projectile to generate shock waves in a target similar to those created by detonating high explosives or meteorite collisions . Swift  discussed the historical development of this type of gun.
Although numerous studies describe the perforation and penetration mechanics of plates during hypervelocity impact, only a few discussed the plastic deformation of plates that do not experience complete penetration under such conditions .
A two-stage light-gas gun, Figure 1, was used to perform the hypervelocity impact experiments. The main components of the gas gun are the powder breech, pump tube, central breech, launch tube, blast tank, and target chamber.
The velocity of the projectile was measured by a laser intervalometer system having two stations separated by a fixed distance. Each station had a laser source that directed a beam through a port to a narrow band-pass filter to ensure that a 32-photodiode array was free of any contamination by external light. Measuring the time interval was initiated by the flight of the projectile across the first station and terminated when it passed through the second station. The time interval was recorded using a digitizer.
When material is loaded in extreme pressure, the shockwave creates an elastic response up to certain limit. This limit is usually defined by HEL, which is usually known as the elastic precursor wave. After this limit, material flows plastically due to the strong shockwave propagation. In the case of uniaxial strain, the peak velocity is followed by multiple loading and unloading phase. The first drop from the peak velocity and subsequent loading-unloading zones are associated with the spall signature in metals. Typically, the first spall signature in metals is followed by a significant sharp drop in free surface velocity, which is defined as the elastic unloading stage.
Gas gun experiments were performed to measure the plastic deformation of A36 steel plates during hypervelocity impacts. The velocity of the back surface of plates was measured using a PDV system. Simulation models were developed in the LS-DYNA SPH solver and the CTH hydrocode. Both models used Johnson-Cook material model and the Mie-Grüneisen equation of state. A procedure for identifying the Hugoniot elastic limit and spall strength of A36 steel was presented. A study was conducted to determine SPH particle sensitivity, and CTH zone spacing studies were conducted to identify the best meshing strategy. The results showed that both simulation approaches were able to accurately match the physical measurements of impact cratering. Moreover, the simulations were able to predict the velocity profiles in the PDV experiments; however, some differences were observed. Additional experiments and fine-tuning of the simulation models were needed, including the use of more accurate material models and simulation parameters. Furthermore, studies were needed on the effect of the pressure induced phase transition that is known to occur in pure iron.
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