Abstract. In this study, a constitutive strength and failure model for a steel core of a14.5 mm API projectile was developed. Dynamic response of a projectile steel core was described by the Johnson-Cook constitutive model combined with principal tensile stress spall model. In order to obtain the parameters required for numerical description of projectile core material behavior, a series of planar impact experiments was done. The parameters of the Johnson-Cook constitutive model were extracted by matching simulated and experimental velocity profiles of planar impact. A series of oblique ballistic experiments with x-ray monitoring was carried out to study the effect of obliquity angle and armor steel plate thickness on shattering behavior of the 14.5 mm API projectile. According to analysis of x-ray images the fragmentation level increases with both steel plate thickness and angle of inclination. The numerical modeling of the ballistic experiments was done using commercial finite element code, LS-DYNA. Dynamic response of high hardness (HH) armor steel was described using a modified Johnson-Cook strength and failure model. A series of simulations with various values of maximal principal tensile stress was run in order to capture the overall fracture behavior of the projectile's core. Reasonable agreement between simulated and x-ray failure pattern of projectile core has been observed.
Recent studies1 have indicated that an array of microlenslets with a near-unity fill factor can be used to direct light more efficiently onto an underfilled array of solid-state photosensors. Radiometric gain may be defined as the total number of rays, directed onto a photosensor area by a lenslet, divided by the total number of rays collected by a bare photosensor, assuming the same ray density. We present the results of ray-based radiometric calculations which model the collection of light by a typical objective lens onto a composite imaging array. This array consists of three optically important layers: the microlenslet layer, a transparent spacer layer, and the detector plane. The radiometric gain is presented as a function of spacer-layer thickness, f/No. of the taking lens, image spot size, and microlens cap height. Radiometric gain values exceeding three are predicted for a typical video imaging array when the lenslet is modeled as a spherical cap truncated to match the pixel area. A lower gain is predicted when an anamorphic-pillow model is assumed. Experimental verification of the spherical gap model is demonstrated for lenslets formed by baking rectangular pads of photoresist. A departure from the model's prediction at large cap heights is explained by a change in the lenslet’s shape.
This paper is a study on ricochet characteristics of metal plates hit by 25 mm APDS-T projectile. A series of ballistic tests has been carried out on three different armor steel types chosen to present a range of hardness. Each armor steel target was impacted at varying angles of incidence until ricochet was observed. This investigation is not only expected to help in understanding the phenomenon of projectile ricochet but also to provide some useful data that can be used for calibration and validation of the finite element (FE) models. In general, the ricochet angle was found to decrease with an increase in target hardness due to different failure mechanism.
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