Search

Principal Component Analysis (PCA) has been applied to thru-transmission ultrasound data taken on ceramic armor. PCA will help find and accentuate differences within the tile, making it easier to find differences. First, the thru-transmission ultrasound data was analyzed. As the ultrasound transducer moves along the surface of the tile, the signal from the sound wave is measured as it reaches the receiver, giving a time signal at each tile location. The information from this time signal is dissected into ten equal segments, and the maximum peak is measured within each segment, or gate. This gives ten measurements at each tile location that correspond to tile depth An image can be made for each of the ten gate measurements. PCA was applied to this data for all of the tile samples, and a performance measure was developed from the loading information. A performance measure was developed and tested on six samples from each of the panels. When these performance measures are compared to the results of the ballistics tests, it can be seen that the performance measure correlates well to the penetration velocities found from the ballistics tests.

A simple go/no-go test for body armor panels using pressure-sensitive, dye-indicator film (PSF) has been shown to be statistically effective in revealing subcritical damage to body armor panels. Previous measurements have shown that static indicator levels are accurately reproduced in dynamic loading events. Further impact tests on armor worn by a human resuscitation dummy using instrumented masses with an attached accelerometer and embedded force transducer have been performed and analyzed. New impact tests have shown a reliable correlation between PSF indication (as digitized images) and impact force for a wide range of impactor energies and masses. Numerical evaluation of digital PSF images is presented and correlated with impact parameters. Relationships between impactor mass and energy, and corresponding measured force are shown. We will also report on comparisons between ballistic testing performed on panels damaged under various impact conditions and tests performed on undamaged panels.

This study aims to characterize the interaction of explosive blast waves through simulated anatomical models. We have developed physical models and a systematic approach for testing traumatic brain injury (TBI) mechanisms and occurrences. A simplified series of models consisting of spherical PMMA shells housing synthetic gelatins as brain simulants have been utilized. A series of experiments was conducted to compare the sensitivity of the system response to mechanical properties of the simulants under high strain‐rate explosive blasts. Small explosive charges were directed at the models to produce a realistic blast wave in a scaled laboratory test cell setting. Blast profiles were measured and analyzed to compare system response severity. High‐speed shadowgraph imaging captured blast wave interaction with the head model while particle tracking captured internal response for displacement and strain correlation. The results suggest amplification of shock waves inside the head near material interfaces due to...

When a projectile approaches the back surface of a target, complicated mechanics and different failure modes ensue that can lead to perforation. There have been a number of attempts to model these different failure modes, for example models due to Ravid and Bodner [1] and Walker [2]. Of particular interest are analytic models (as opposed to hydrocode models) where the model attempts to explicitly identify relevant failure modes and back surface breakout modes. This paper examines back surface breakout and target failure models with different failure modes to see how they are invoked in specific impact geometries and scenarios. Comparisons are made of thresholds and sensitivities for the different failure modes to gain a greater understanding of their usefulness and applicability. The model results are compared to data to ensure reasonableness of the computations. Good agreement is shown with a relatively simple back‐surface‐strain target failure mode for predicting ballistic limit velocity for large aspect‐ratio projectiles and relatively thick targets as compared to the projectile diameter.

Operation of a two‐stage implosion‐driven hypervelocity launcher in which the launch tube is imploded behind the projectile is examined. In particular, techniques to generate a high phase velocity of implosion are explored, and the technique of using a variable thickness flyer plate with a constant thickness layer of explosive is selected for further investigation. An analytic model, based on the Gurney analysis for flyer plate acceleration, is developed to determine the thickness profile necessary to deliver the desired phase velocity. Finite element simulations and experimental implementation of this approach results in the correct increase in phase velocity along the launch tube, however, the velocity profile does not generate the desired constant acceleration profile.

We present the results of development of explosive systems for investigating multiple action of solid projectiles upon an obstacle at a moderate impact velocity on the order of 1 km/s. Two types of systems are considered, namely: 1) evacuating shock tube with plane high explosive (HE), 2) ballistic gun with distributed shot of plastic HE. In the first system an acceleration of steel spheres are realized in flux of expanding explosive products. The second system provides the acceleration of a “soft” plastic block with steel spheres having certain mutual orientation. The experiments with these explosive systems testify to higher effectiveness of projectiles penetration into obstacles at multiple impact with a moderate velocity.

Some of the recent efforts to improve the ballistic performance of lightweight armors utilize functionally graded materials to provide a continuous transition in properties between dissimilar materials. It has been conjectured that the elimination of abrupt acoustic impedance changes may result in beneficial stress wave attenuation. We examine this issue for some idealized one‐dimensional problems in which all materials are linear elastic. Exact solutions are compared with DYNA3D simulations of the same problems.

The dynamic behavior of a solution heat‐treated, water‐quenched and aged U‐0.75wt%Ti alloy was studied in planar (disk‐on‐disk) and reverse ballistic (disk‐on‐rod) impact experiments performed with a 25 mm light‐gas gun. The impact velocity ranged from 100 to 500 m/sec. The impacted samples were softly recovered for further metallographic examination. The VISAR records of the sample free surface velocity, obtained in planar impact experiments, were simulated with 1‐D hydrocode for calibrating the parameters of modified Steinberg‐Cochran‐Guinan (SCG) constitutive equation of the alloy. The same SCG equation was employed in 2‐D AUTODYN simulation of the alloy response in the reverse ballistic experiments, with VISAR monitoring of the lateral sample surface velocity. Varying the parameters of the strain‐dependent failure model allows relating the features of the recorded velocity profiles with the results of the examination of the damaged samples.

With the development of plasticity theory in the 1940s and 1950s, the modeling of penetration has become increasingly analytical and accurate. Currently, analytic penetration models are able to accurately predict depths of penetration for simple penetration geometries where the target and projectile are metals. The most accurate models use sophisticated plasticity analysis to obtain target resistances, but they usually end up expressible as relatively simple explicit differential equations. The most promising development in recent years is the centerline momentum balance, and this technique will be reviewed with some discussion of the meaning of terms by way of first principle physics. A recent model that successfully predicts ballistic limits of fabrics will also be discussed. In addition to addressing what is known, the most pressing questions that need to be answered and what is currently known on those problems will be discussed. Questions include: the transition from eroding to rigid penetration; the...

We present a model for the steady-state penetration phase of yawed long rods. The projectile-target interaction is comprised of axial deceleration and erosion due to frontal pressure, and lateral deceleration due to cavity expansion pressure. By solving the resulting ODEs through time-stepping, the evolution of the projectile/crater shape is obtained.

It is well known that impact inclination is detrimental to penetration performance for long-rod projectiles into semi-infinite targets. The drop-off in performance, measured as the depth of penetration normalized by the initial projectile length, is generally attributed to interference of the tail of the projectile with the side walls of the penetration cavity. However, little has been done to study the effect of impact inclination on the performance of long rods penetrating finite targets. A reverse ballistic experiment and three-dimensional numerical simulations are used to examine the effect of impact inclination against an oblique plate. In particular, the interaction of the projectile with the plate, to include asymmetric enlargement of the penetration channel and side loading of the projectile, are examined in the simulations, and compared to experimental results.

The loading history for the hypervelocity impact of a long-rod striking a moving flat plate at an oblique angle was analyzed using the EPIC code. The loads were reduced to their axial and lateral components to provide insight into the penetration problem as well as indicate temporal regimes where loading must be considered in the design and analysis of long rod penetrators. Furthermore, the effect of an EPIC input parameter, the erosion strain, used for the numerical treatment of eroding interfaces was assessed with attention focused on the predictions of peak loads, mass loss, and final configuration of the rod.

When a long-rod penetrator impacts a target at a high yaw angle, interference of the penetrator with the sidewall of a crater is the mechanism for the degraded penetration performance. The yawed penetrator is described as a series of cylindrical elements. Using this assumption, the model considers the effective diameters of the penetrator whether or not it interacts with the crater wall and a revised crater profile is calculated with the effective diameters.