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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]

• High hardness steel (HHS) sheet with UHMWPE composite backing were tested against a hardened steel core projectile. • The projectile core was eroded by the HHS sheet and stopped in UHMWPE composite. • It is observed that only a core eroded to a certain length and weight by armor system can be defeated. • In numerical modeling core failure strain was determined from the residual weight of cores. • The numerical model can be used to evolve armor design. Thin high hardness steel sheets can be an alternative to expensive ceramic armor systems designed to defeat hardened core projectiles. A thin high hardness steel sheet backed with UHMWPE fiber-reinforced composite was ballistically tested against a 7.62 × 39 mm hardened steel core projectile in a single-stage gas gun. Thin steel sheets of 530 BHN hardness were adhesively bonded with UHMWPE fiber-reinforced composite to fabricate armor plates. Armor plates were able to defeat the projectile showing considerable potential. Tensile strength of steel sheet and UHMWPE-fiber reinforced ply was also determined. A detailed numerical simulation of the impact event was also performed to understand the phenomenon of defeat and penetration in greater detail. The numerical model was calibrated from the recovered projectile's core after the ballistic test. [ABSTRACT FROM AUTHOR]

Abstract: A micro-scale computational tool, based upon an explicit digital element method (DEM), has been developed for numerical simulation of ballistic impact and penetration of textile fabrics. In this approach, each yarn is digitized as an assembly of digital fibers. Each digital fiber is further digitized into a short digital rod element chain connected by frictionless pins (nodes). A search is conducted to find contacts between adjacent digital fibers. If a contact is detected, compressive and frictional forces between fibers will be determined, based upon contact stiffness and friction coefficient. Nodal forces are calculated for each time step. Nodal displacements are determined using an explicit procedure. Because the digital element approach operates on a sub-yarn micro-scale, one can determine textile penetration resistance based upon sub-yarn scale properties, such as inter-fiber compression, friction, and fiber strength. Research presented in this paper includes three parts. First, the explicit digital element algorithm used in dynamic simulation is explained. Second, the approach is used to generate 2-D woven fabric micro-geometries and to simulate ballistic penetration processes. Third, numerical results are compared to high resolution experimental impact and ballistic test data. [Copyright &y& Elsevier]