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• The protection capability of modified aramid fabrics against fragment simulating projectiles and full metal jacketed bullets. • The design of layers considering both critical velocity and back face deformation. • The priority of intercepting bullets and reducing blunt trauma. Soft body armor is required to meet threats of both bullets and explosion fragments in battlefield. However, designing body armor that can protect against these two types of projectiles considering both critical velocity and back face deformation (BFD) is often based on experience and extensive ballistic experiments. This paper proposes a quick design model for determining the layers of aramid fabrics modified by polyethylene (PE) to protect against fragment simulating projectiles (FSP) and full metal jacketed bullets (FMJ). Firstly, ballistic experiments are conducted discovering the optimal concentration of PE modification against the sphere and FSP is 10 %. Secondly, finite element model is adapted to explore the protection capabilities of modified aramid fabrics against FSP and FMJ and a linear relationship between the BFD and the critical velocity has been observed. Thirdly, an analytical model is established to uncover the reason of this relationship. Finally, a design model is proposed to configure the improved outer tactical vest (IOTV) generation III based on the derived formulae of critical velocity and BFD for different layers of modified aramid fabrics against FSP and FMJ. The model indicates that the objectives of intercepting FSP or FMJ and reducing blunt trauma are usually not simultaneously attainable. 38 layers of modified aramid fabrics are sufficient to meet the protection requirements for both FSP and FMJ, regardless of critical velocity and BFD. Besides, 498 m/s is the threshold of FMJ impact velocity to determine the priority of intercepting bullets or reducing blunt trauma. The design model can serve for the development of lightweight and effective body armor. [ABSTRACT FROM AUTHOR]

• Four surface wave profiles were investigated for hypervelocity impact shielding. • Wave profiles caused novel projectile fragmentation and debris cloud shape. • Wavy plates outperform flat plate in terms of energy dissipation. • Simple design variations allow wavy plates to perform considerably better. Continuously increasing micro meteorite and orbital debris (MMOD) in space poses a threat to any manned or unmanned space vehicle with increasing probability of damaging object impact. To address the sufficient level of protection of space vessels, many Whipple shield configurations has been studied for over half a century. Bumper plate of Whipple shields studied in existing literature are flat surfaced plates. In contrast to earlier studies, this paper investigates the reaction of bumper plates with wavy surfaces against hypervelocity impact by analysing how they contribute to projectile fragmentation, formation of debris cloud, and how they dissipate the impact energy. Aluminium plates with four different surface wave profiles (WPs) were numerically investigated under hypervelocity impact conditions to assess their performance on disintegration of the impacting projectile. Fragmentation patterns of spherical aluminium projectile and debris cloud generated by projectile-wavy plate couples were examined and compared with the equivalents observed in flat-surfaced plate impact. A hybrid Smoothed Particle Hydrodynamics (SPH) combined with finite element modelling (FEM) approach was adopted using ANSYS software to simulate hypervelocity impact phenomenon at 3 km/s. Results of the numerical work carried out in this study revealed the distinctive debris cloud generation that has never been reported before in the existing literature. Furthermore, compared to the flat plate, wavy plates are found to be more effective in decreasing the impact energy. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a ballistic impact simulation of an armour-piercing projectile in hybrid ceramic/fiber reinforced composite armour. The armour is composed by an alumina plate and an ultra high molecular weight polyethylene composite. In order to model the armour behavior three different constitutive models were formulated and implemented into ABAQUS/Explicit finite element code. Comparisons between numerical predictions and experimental results in terms of damage shape/extent and V50 are also presented and discussed in the paper. [Copyright &y& Elsevier]

Highlights • A series of rigid projectile penetration tests on concrete targets pre-damaged by explosively formed projectile (EFP) is conducted. • Impact performance of the individual rigid projectile and two-stage munitions, as well as the influences of concrete type, projectile striking velocity and target configuration are experimentally studied. • Penetration process of the following rigid projectile into the pre-damaged target is numerically reproduced with the restart input data method implemented in the finite element program LS-DYNA. • Influences of the liner material and configuration of shaped charge, as well as the rigid projectile diameter on the impact performance of two-stage munitions are further discussed. Abstract The two-stage munitions is newly utilized to attack the hard and deeply buried protective structures, while the related work on the impact performance of two-stage munitions into concrete targets is still limited. This paper addresses the impact performance of one typical two-stage munitions, which consists of a precursor explosively formed projectile (EFP) and a following rigid projectile. Firstly, based on our previous EFP impacting test on the concrete targets (Hu et al., IJIE, 2017), a series of rigid projectile penetration tests on these pre-damaged concrete targets is further conducted. By assessing the dimensions of the penetration boreholes, the influences of concrete type (normal strength concrete (NSC) and reactive powder concrete (RPC)), target configuration (monolithic and spaced) and rigid projectile striking velocity (300 m/s–500 m/s) on the targets damage subjected to the two-stage munitions are experimentally discussed. Then, by adopting the restart input data method implemented in the finite element (FE) program LS-DYNA, the targets damage subjected to the precursor EFP is recorded and the penetration process of the following rigid projectiles into the pre-damaged targets is numerically reproduced. Finally, based on the validated restart input data method, material models and the corresponding parameters, the impact performance of the two-stage munitions with different liner materials (T2 copper and 2A12 aluminum) and configurations (spherical segment, conic and truncated) of shaped charge as well as the following rigid projectile diameters (0.1∼0.9 times the shaped charge diameter) is further discussed, respectively. [ABSTRACT FROM AUTHOR]

Highlights • An existing Reissner Mindlin shell element is enriched using X-FEM to model dynamic crack propagation in thick shells. • A diagonal mass matrix is used for the enriched displacement and rotational DOFs. • An explicit representation of the crack lying on the shell?s mid-surface is done using a 1D mesh. • A crack propagation criterion able to account for tensile and shear driven fracture is used. Abstract This paper is devoted to the modeling of crack propagation under impact loadings in thick shells composed of metallic materials using X-FEM. The proposed thick shell element is based on the existing Q 4 γ 24 4-node shell element for fast transient loadings that is enriched in the present work using X-FEM. The shell is considered to be always cut by a through the thickness crack. This element is hence enriched only with jump Heaviside functions on all degrees of freedom (displacements as well as rotations). The mass matrix corresponding to all added DOF is simply a copy of the usual continuous DOF diagonal mass matrix. The crack is discretized explicitly with a simple 1D mesh that lives on the shell's mid-surface and independently of the finite element mesh. Plasticity as well as stress field used for crack propagation criterion is evaluated using 5 Simpson points across the thickness. The crack propagation criterion is based on the measure of an equivalent stress at the crack tip and can predict both tensile and shear driven fracture as well as transitions between those two regimes. Comparisons with elastoplastic crack propagation experiments involving fracture under transient loadings show that the method is able to reproduce experimental fracture quite well. [ABSTRACT FROM AUTHOR]

This paper addresses the impact performance of explosively formed projectile (EFP) formed by shaped charge (SC) on the concrete targets. Firstly, a series of EFP penetration/perforation test on concrete targets are conducted. By assessing the dimensions of front spalling and rear scabbing craters as well as the penetration borehole, the influences of SC liner material, concrete type and target configuration (monolithic and spaced) on the target damage are experimentally discussed. Secondly, by utilizing the multi-material Arbitrary Lagrange-Euler (ALE) algorithm, Fluid-Structure Interaction (FSI) method and erosion algorithm implemented in the finite element (FE) code LS-DYNA, and describing the concrete targets with the original and modified HJC models, the formation and impact processes of EFP are well reproduced. Furthermore, based on the validated constitutive models and the corresponding parameters, the influences of explosive type, liner configuration and thickness, first concrete panel and air interlayer thicknesses of spaced target on the impact performance of EFP are further discussed. The derived conclusions could provide helpful references for the analysis and design of the concrete protective structures, and the evaluation of the ballistic performance of EFP. [ABSTRACT FROM AUTHOR]

This paper presents the results of an investigation of the ballistic limits and failure modes of AA2024-T351 sheets impacted by cubical projectiles. The effect of cube orientation on the ballistic limit and failure modes was considered in detail. Three impact configurations were investigated. Configuration one, two and three considered face, edge or corner impacts correspondingly. The experimental results were complemented with finite element analysis results in order to explain the observations. The lowest ballistic limit (202 m/s) was observed when the cube edge impacted on the target. In the cube face impacts, the ballistic limit was higher (223 m/s), and the highest ballistic limit (254 m/s) was observed for the corner impact. Although the face impact did not have the lowest ballistic limit, this impact configuration resulted in the least amount of projectile energy loss for impacts above the ballistic limit. With the aid of finite element modelling, it was possible to develop a better understanding of the test results and explain that the observed differences in impact response were not just due to a difference in projectile frontal area, but also due to the combination of the localised deformation near the projectile impact point and the resulting global (dishing) deformation. [ABSTRACT FROM AUTHOR]

This paper presents an innovative approach for 3D Lagrangian finite element modelling of the fragmentation of a blunt shaped projectile (BSP) made of a tungsten heavy alloy impacting against a ceramic Alumina tile. The aim of this work is to develop an alternative way of modelling the fragmentation of both the projectile and the ceramic tile, with respect to the classical approach of the deletion of the finite elements. In particular, the projectile is made of an assembly of pre-fragmented sub-parts, without the possibility of deletion of the finite elements, with a cohesive law that allows the separation of the sub-parts when the suitable failure criterion is met. The ceramic tile model adopts the transformation of the finite elements into SPH (smooth particle hydrodynamics) elements when the failure criterion is met. Both these approaches are adopted to conserve the mass and to avoid discontinuities of the contacts between the parts. The heat generation by plastic work and the rate dependent properties of the materials are reproduced in the analyses. The model is compared with experimental data from the literature, in particular validating its performance in predicting the residual velocity and the residual mass of the projectile; an analysis of the wave propagation and damage morphology has also been carried out. [ABSTRACT FROM AUTHOR]

• A simple numerical framework is established based on a semi-empirical model. • Dynamic behaviors of rigid projectiles impacting concrete targets are predicted. • Effects of crater formation and the presence of a free surface are considered. • The influences of projectile geometries and impact conditions are investigated. • The critical angle and velocity that enable projectile ricochet are identified. This paper presents a simple and efficient semi-empirical model for predicting the dynamic behaviors of rigid ogive-nosed projectiles after obliquely impacting semi-infinite concrete targets. We consider the normal stress acting on the projectile surface as a result of the target resistance. We also reflect the decrease in normal stress caused by crater formation and the presence of the free surface on the target. The normal stress is formulated as a function of the projectile geometry and the properties of the target material. To verify the proposed semi-empirical model, we establish computational frameworks combining the finite element method and smoothed particle hydrodynamics. These frameworks are confirmed to provide results consistent with the experimental data for the normal impact of projectiles on concrete targets. By comparing the results obtained from the semi-empirical model with the reference results obtained from the computational frameworks, we demonstrate that the semi-empirical model can successfully predict the penetration or ricochet of projectiles following oblique impact. Furthermore, considering the nose sharpness, slenderness, impact velocity, and oblique incidence angle of the projectiles as key parameters, we investigate their effects on the dynamic behaviors of projectiles. The penetration capabilities of projectiles increase with sharper and slenderer geometry, higher impact velocity, and lower incidence angle. In particular, considering various combinations of these parameters, we identify the critical conditions for the incidence angle and impact velocity that lead to the ricochets of projectiles. The minimum incidence angle, at which ricochets occur, increases in proportion to the nose sharpness, slenderness, and impact velocity. The maximum impact velocity, up to which ricochets occur, decreases as the nose sharpness and slenderness increase and the incidence angle decreases. [ABSTRACT FROM AUTHOR]

Abstract: This paper presented a three-dimensional (3D) finite element analysis approach to study the projectile penetration into rock-rubble overlays considering the randomness of rock-rubble in shape and distribution. The generation algorithm of 3D rock-rubble with random size and shape was firstly proposed. The dropping and compacting algorithms for the random distribution of all particles of rock-rubble in an overlay were then developed. Thirdly, a finite element grid was formed using the mapping algorithm. An analysis approach for the 3D finite element model of the random distribution of all particles of rock-rubble in an overlay was established by employing the hydrocode LS-DYNA taking into account the different materials properties and contact effect. In order to validate the analysis approach, the numerical results were compared with the limited test data, and a good agreement was obtained. Finally, numerical studies of the projectile penetration into the grouted concrete rock-rubble overlays were presented under different impact conditions, focusing on the penetration depth, yawing angle, trajectory and projectile deformation. It is indicated that impact obliquity affects the penetration depth, terminal yawing angle and penetrator deformation greatly. In order to reveal the stopping and deflecting mechanism of rock-rubble overlays, parametric studies were carried out to analyze the effects of different impact conditions and target configurations on projectile penetration. The numerical results show that the size, strength and volume percentage of rock-rubble and grouted concrete strength are critical to penetration depth and terminal yawing angle. [Copyright &y& Elsevier]

Abstract: Numerical simulations of oblique-angle penetration by deformable projectiles into concrete targets are performed in this paper by using the three-dimensional finite element code LS-DYNA, into which a combined dynamic constitutive model which can simultaneously describe both the compressive and tensile damage of concrete is implemented. As a consequence, the ballistic trajectories and the depths of penetration under different oblique angles (from 10° to the ricochet angle) are obtained. Moreover, the damage distribution of concrete after oblique penetration is procured, which can really reflect the tensile and compressive damage of concrete. The numerical results for the depths of penetration are compared with experimental data obtained by previous authors and show good agreement. [Copyright &y& Elsevier]

Abstract: This paper examines the penetration and perforation of fibre-reinforced plastic (FRP) laminates struck by rigid projectiles with different nose shapes within a wide range of impact conditions using ABAQUS/Explicit code. It is assumed that the FRP laminate target response can be represented by a velocity dependent forcing function which eliminates discretizing the target as well as the need for a complex contact algorithm. The forcing function is then applied to the surface of the projectiles as boundary conditions in the numerical model. With this combined analytical and computational technique we can obtain the depth of penetration, residual velocity, ballistic limit, transient response in terms of time-histories of displacement/penetration, velocity and deceleration of the projectile. It is shown that the model predictions are in good correlation with available experimental data. [Copyright &y& Elsevier]