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The investigation on free-surface impact of projectiles has last for more than one hundred years due to its noticeable significance on improving defensive weapon technology. Laboratory-scaled water entry experiments for trajectory stability had been performed with four kinds of projectiles at a speed range of 20~200 m/s. The nose shapes of the cylindrical projectiles were designed into flat, ogive, hemi-sphere and cone to make comparisons on the trajectory deviation when they were launched into water at a certain angle of 0~20°. Two high-speed cameras positioned orthogonal to each other and normal to the water tank were employed to capture the entire process of projectiles' penetration. From the experimental results, the consecutive images in two planes were presented to display the general process of the trajectory deviation. Compared with the effect of impact velocities and nose shape on trajectory deviation, it merited conclude that flat projectiles had a better trajectory stability, while ogival projectiles experienced the largest attitude change. The characteristics of pressure waves were also investigated. [ABSTRACT FROM AUTHOR]

The investigation on ballistic stability of high-speed projectile in granular materials is important to study the EPW (earth-penetrating weapon). Laboratory-scaled sand entry experiments for the trajectory in the sand have been performed at a range of velocities from 30 m/s to 150 m/s. In addition, pressure sensor was embedded in the sand to record the sand stress which reflects the penetration performance of projectile during the impact. The slender projectiles were designed into flat nose shape with three kinds of L/D (length-diameter ratio) to make comparisons on the trajectory when those projectiles were launched at normal and oblique impact angles (0~25deg) along a view window. A high-speed camera beside window was employed to capture the entire process of projectiles' penetration. Basing on the comparison of different tests, theoretical analysis is carried out on the relationship between ballistic stability and associated conditions. By utilizing DIC technique, the vector field of sand velocity was acquired, and the spreading direction of the impacting energy was observed. It can be concluded that the sand stress is the function of penetrating velocity, L/D and the shot angle. It increases with the growing of penetrating velocity and L/D, decreases with the shot angle. To a certain extent, the biggest initial velocity leads to the highest stress. [ABSTRACT FROM AUTHOR]

The penetration and fragmentation characteristics of spheres made of pressed aluminum powder are studied via normal impact on thin steel plates at 0.6 to 1.8 km/s. Ultra-high speed photography and flash x-rays are used to monitor the formation and evolution of the debris cloud formed by impact. The mass distribution of debris fragments is measured directly via a soft-catch experiment. Experimental results are compared to simple analytic theories of brittle fragmentation and spall. This data aids in understanding the mechanical properties and potential energy release of porous reactive materials. [ABSTRACT FROM AUTHOR]

Tungsten projectiles were shot into sand at velocities between 600 and 2200 m/s. Penetration was maximum at about 775 m/s. Below that velocity, projectiles were apparently stabilized by a fin set. Above that velocity, projectiles were broken by transverse loads. High-speed penetration resulted in comminution of sand particles, reducing their size by about 1000 times. [ABSTRACT FROM AUTHOR]

Strength of glass and glass ceramic was measured with a bar impact technique. High-speed movies show regions of tensile and compressive failure. The borosilicate glass had a compressive strength of at least 2.2 GPa, and the glass ceramic at least 4 GPa. However, the BSG was much stronger in tension than GC. In ballistic tests, the BSG was the superior armor. [ABSTRACT FROM AUTHOR]

High-velocity impact onto a layered glass target produces a very extensive damage pattern exhibiting many distinct morphologies. High-speed photography reveals failure waves and cracks that move at acoustic velocities. These prompt features evolve into a complex final damage pattern that includes needle fragments around the penetration cavity, radial cracks at mid distance, and dicing cracks near the edges. [ABSTRACT FROM AUTHOR]

An analytical model of normal ballistic impact on the ceramic/metal gradient armor, which is based on modified Alekseevskii-Tate equations, has been developed. The process of gradient armour impacted by the long rod can be divided into four stages in this model. First stage is projectile's mass erosion or flowing phase, mushrooming phase and rigid phase; second one is the formation of comminuted ceramic conoid; third one is the penetration of gradient layer and last one is the penetration of metal back-up plate. The equations of third stage have been advanced by assuming the behavior of gradient layer as rigid-plastic and considering the effect of strain rate on the dynamic yield strength. [ABSTRACT FROM AUTHOR]

The failure characterization of brittle materials like glass is of fundamental importance in describing the penetration resistance against projectiles. A critical question is whether this failure front remains “steady” after the driving stress is removed. A test series with short gold rods (D = 1 mm, L/D≈5–11) impacting borosilicate glass at ∼1 to 2 km/s was carried out to investigate this question. The reverse ballistic method was used for the experiments, and the impact and penetration process was observed simultaneously with five flash X-rays and a 16-frame high-speed optical camera. Very high measurement accuracy was established to ensure reliable results. Results show that the failure front induced by rod impact and penetration does arrest (ceases to propagate) after the rod is totally eroded inside the glass. The impact of a second rod after a short time delay reinitiates the failure front at about the same speed. [ABSTRACT FROM AUTHOR]

A series of DOP tests with lateral confinement have been carried out and a linear relation between the residual penetration in RHA and the alumina thickness has been obtained. The rod configuration and the initial transient impact are the two factors that cause the gradual decrease of the differential efficiency factor (DEF) when the ceramic thickness is increased in literature. A new improved DEF definition is proposed to characterize the thick tile ceramic ballistic performance based on a more physical analysis. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Computational solid mechanics (CSM) for ballistics, as it exists today, does not have predictive capabilities that are comparable to those of computational fluid dynamics (CFD). The most important reason for this is the lack of high quality physical models for the damage and failure processes that occur during high-speed impact. An approach for modeling impact damage in metals, based on physical modeling of adiabatic shear bands and voids, will be presented. Scaling laws for damage from shear bands have been developed over the past decade from detailed analysis of the thermomechanical processes, and are being adapted for efficient use in large-scale computations. A similar approach for ductile void growth and spall has also been initiated. This approach is expected to lead to models that are based on the essence of the physics, rather than on fitting of phenomenological models to large databases. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

The technique of Digital Speckle Radiography (DSR) has been shown to be widely applicable to the field of ballistics through its ability to measure internal displacement fields to a high precision. In a DSR experiment, a flat plane, typically 500 μm thick, of X-ray opaque filings are introduced into the sample during manufacture. Flash X-rays can then be used to image the plane, both before and during an impact event, to produce random speckled images on an X-ray film. Small sub-regions of the images can be tracked relative to each other using a Digital Speckle Photography (DSP) correlation algorithm. This produces a displacement field within the specimen on the seeded plane. By repeating an experiment with identical specimens, but varying the delay of the X-ray exposure, a full time history of the impact event can be obtained. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

There is a correlation between the variation of penetration with impact velocity and the variation with target strength. This is because penetration is dependent on the ratio of inertial to strength forces. By using a Taylor series expansion, one can use penetration-velocity data to predict penetration-strength relationships. [ABSTRACT FROM AUTHOR]