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Modeling clay is a soft malleable material made from oils and waxes. This material is fundamental for ballistic evaluation of body armors because it is used as backing material in ballistic tests. After a ballistic impact, a back-face indentation is measured to assess performance of the armor. Due to the important role of modeling clay in this particular application, its mechanical characterization and comprehension of penetration mechanics are essential for development of new personal protection systems. This paper presents a two-step computational methodology to calibrate parameters of a Cowper–Symonds material model for modeling clay at characteristic strain rates up to 1.8 × 10 4   s − 1 . In the first stage, a high-speed camera is used to record the penetration of a gas-gun launched cylindrical mass with a hemispherical cap into a block of clay. Image-processing software is used to capture the tail of the projectile as it penetrates into the clay. These data are then used to sample the penetration depth as function of time. In the second stage, an in-house developed model of penetration, based on both the spherical cavity expansion theory and the Tate penetration equation, is used to determine, by inverse analysis, the parameters of the Cowper–Symonds clay model. The proposed constitutive relationship for clay and the determined material parameters can be applied accurately to problems involving high strain rates. [ABSTRACT FROM AUTHOR]

Ballistic performance of an armour steel at different tempering conditions against a tungsten heavy alloy long rod kinetic energy projectile has been investigated. The ballistic performance was found to increase with decreasing tempering temperature but the performance increments were not proportional to the strength increase caused by the tempering. Both target and projectile underwent fragmentation at the penetration interface in all the three targets. Apart from the strength target material deformation behaviour also showed considerable influence on ballistic performance. The ballistic performance appears to increase with decreasing toughness for a given strength. [ABSTRACT FROM AUTHOR]

The database for depth of penetration by projectiles into semi-infinite targets is quite extensive. The objective is to use the experimental semi-infinite penetration data to predict finite-thickness target effects. Similitude considerations are used to represent penetration response as a function of a normalized impact velocity, which is the ratio of the penetration pressure to the target strength. Then, a least-squares regression analysis methodology was applied to the normalized experimental data to provide an analytic expression for the normalized depth of penetration as a function of the normalized impact velocity over a very large velocity range, typically a few hundred meters per second to over 3500 m/s. We use the analytic expression, along with some simplifying assumptions, to estimate ballistic limit thickness T 50 and/or the ballistic limit velocity V 50 . If a target is overmatched, i.e., perforated by the projectile, an estimate is also made for the projectile residual velocity and residual length. The experimental data on which the regression fit is based consists of L / D 10 projectiles, so a procedure is also developed to account for different projectile aspect ratios. A series of examples are provided to demonstrate the utility and accuracy of the approach. [ABSTRACT FROM AUTHOR]

Abstract: Reverse ballistic experiments were used to investigate confinement, pre-damaged and intact, and rod size effects on penetration of long, gold rods into silicon carbide (SiC-N). Rod diameters were 1.0mm and 0.75mm, and lengths were 70mm and 50mm, respectively. Within data scatter, penetration velocity was the same for intact (bare or sleeved), pre-damaged (thermally shocked with non-contiguous cracks), and in situ comminuted SiC-N. Penetration velocity was independent of rod diameter within the data scatter. An expression for the penetration velocity versus impact velocity is found using linear regression. It is proposed that the reason there is no difference in the penetration rate between intact and pre-damaged (failed) SiC is because, after the first few microseconds following impact, the rod penetrates failed material in both cases. [Copyright &y& Elsevier]

Abstract: Impact, damage evolution and penetration of thick-section composites are investigated using explicit finite element (FE) analysis. A full 3D FE model of impact on thick-section composites is developed. The analysis includes initiation and progressive damage of the composite during impact and penetration over a wide range of impact velocities, i.e., from 50 m/s to 1000 m/s. Low velocity impact damage is modeled using a set of computational parameters determined through parametric simulation of quasi-static punch shear experiments. At intermediate and high impact velocities, complete penetration of the composite plate is predicted with higher residual velocities than experiments. This observation revealed that the penetration-erosion phenomenology is a function of post-damage material softening parameters, strain rate dependent parameters and erosion strain parameters. With the correct choice of these parameters, the finite element model accurately correlates with ballistic impact experiments. The validated FE model is then used to generate the time history of projectile velocity, displacement and penetration resistance force. Based on the experimental and computational results, the impact and penetration process is divided into two phases, i.e., short time Phase I – shock compression, and long time Phase II – penetration. Detailed damage and penetration mechanisms during these phases are presented. [Copyright &y& Elsevier]

In this paper, the influence of mesh sensitivity on the fracture predictions during penetration and perforation of hardened blunt-nose cylindrical steel projectiles in plates of Weldox 460E, Weldox 700E, and Weldox 900E steel has been studied. The main objective is to try to describe the experimentally obtained trend of a decrease in ballistic limit velocity with increased target strength when the plates are impacted by blunt projectiles. This behavior is due to the occurrence of highly localized shear bands as the target strength increases. The impact tests are analyzed using the explicit solver of a nonlinear finite element code. A thermoelastic-thermoviscoplastic constitutive model with coupled or uncoupled ductile damage was used in the simulations. It was found that the residual velocity continuously increases when the element size is decreased from 125 μm to 15μm in the shear zone, and that this increase is significantly stronger for impact velocities close to the ballistic limit. The ballistic limit decreases by up to 25% when the size of the element is decreased from 125 μm to 30 μm; the decrease being somewhat greater for the two steels with the highest strength. Even with the finest mesh, the experimental trend of a decreasing ballistic limit with increasing target strength was not predicted in the simulations, neither with coupled nor uncoupled damage. Nonlocal simulations based on smoothing of the damage and temperature fields, which are the two variables causing the softening, were carried out for the Weldox steels and a mesh size of 30 μm. These simulations indicate a reduction in the mesh sensitivity for both the coupled and uncoupled damage approaches when nonlocal averaging is employed. [ABSTRACT FROM AUTHOR]

The important mechanisms for defeating armor piercing (AP) projectiles are reviewed in this paper. These mechanisms are based on the compressive strength of the target material (its inherent resistance to penetration) and on the asymmetrical forces which it exerts on the threat, through proper geometrical arrangements. We discuss the basic features of the resistance to penetration, starting with the classical analysis of the cavity expansion process in elasto-plastic solids. This property of the target is responsible for the deceleration of hard cored projectiles and for the erosion of long rods, under normal impact conditions. We then discuss the asymmetrical interaction of AP projectiles with inclined plates (metals and polymers) and with ceramic spheres. These asymmetric forces are responsible for their deflection and breakup. Our work combines experimental observations with numerical simulations and engineering models, which enhance the understanding of the various phenomena encountered in these complex situations. This understanding is necessary for optimizing the performance of any armor design against a given threat. [ABSTRACT FROM AUTHOR]

A computational approach for the engineering analysis of ablative-type thermal protection systems (TPS) in atmospheric reentry ballistic flights is communicated. We first propose an improved lumped differential approach for ablative thermal protection analysis, which involves the use of materials with low thermal diffusivity. The results obtained for a one-dimensional thermal ablation problem in a finite slab are compared against those obtained by previously reported lumped differential solutions. Benchmark results for the local nonlinear model, obtained through the generalized integral transform technique, are utilized to verify the proposed solution in a realistic ablation problem, consisting of a low thermal diffusivity material subjected to a prescribed net aerodynamic heating. In addition, an integrated symbolic–numerical system is constructed based on the Mathematica platform for the derivation and computation of all the related quantities along the flight, yielding the transient behavior of the TPS recession and thermal performance for both the constant and variable initial thickness along the vehicle nose region. An illustrative example of the computational tool and the typical results for an orbital platform in ballistic reentry flight are presented. [ABSTRACT FROM AUTHOR]

With the increase of impact velocity, penetration mechanism may change at a transition point from nondeformable projectile penetration regime to semihydrodynamic penetration regime. Analysis is presented to predict this transition point. Good agreements between analytical predictions and experimental results are obtained. [ABSTRACT FROM AUTHOR]