Perforation of 12mm thick steel plates by 20mm diameter projectiles with flat, hemispherical and conical noses: Part I: Experimental study
ABSTRACT Projectiles with three different nose shapes (blunt, hemispherical and conical) have been used in gas gun experiments to penetrate 12 mm thick Weldox 460 E steel plates. Based on the experimental results, the residual velocity curves of the target material were constructed and compared. It was found that the nose shape of the projectile significantly affected both the energy absorption mechanism and the failure mode of the target during penetration. The ballistic limit velocities were about equal and close to 300 m/s for hemispherical and conical projectiles, while it was considerably lower for blunt projectiles. Blunt projectiles caused failure by plugging, which is dominated by shear banding, while hemispherical and conical projectiles penetrated the target mainly by pushing the material in front of the projectile aside. Also, the residual velocity curves were influenced by nose shape, partly due to the differences in projectile deformation at impact. The experimental study, given in this part of the paper forms the basis for explicit finite element analysis using the commercial code LS-DYNA presented in Part II of the paper.
Article: Experimental investigations on the ballistic impact performances of cold rolled sheet metals[show abstract] [hide abstract]
ABSTRACT: This study focuses on the ballistic performances of 1 and 2 mm-thick and 2 x 1 mm-thick cold rolled sheet metal plates against 9 mm standard NATO projectile. The velocity of the projectile before and after perforation, the diameter of the front face deformation, the depth of the crater and the diameter of the hole were measured. The fracture surfaces of the plates near the ballistic limit were also microscopically analyzed. The highest ballistic limit was found in 2 mm-thick plate (332 m s(-1)) and the lowest in 1 mm-thick plate (97 m s(-1)). While, the ballistic limit of 2 x 1 mm-thick plate decreased to 306 m s(-1). Typical failure mechanism of the projectile was the flattening and mushrooming at relatively low velocities and the separation from the jacket at relatively high velocities. In accord with the ballistic limits, 2 mm-thick target plate exhibited the highest hardness value. Microscopic investigations showed the significant reductions in the grain size of the targets after the test. (C) 2010 Elsevier Ltd. All rights reserved.Materials and Design 01/2011; 32(3):1356-1366. · 2.20 Impact Factor
Article: Energy absorption during projectile perforation of thin steel plates and the kinetic energy of ejected fragments[show abstract] [hide abstract]
ABSTRACT: This paper concerns energy absorption in thin (0.4 mm) steel plates during perforation by spherical projectiles of hardened steel, at impact velocities between 200 and 600 m s−1. Absorbed energies have been obtained from measured incident and emergent projectile velocities. These tests were simulated using ABAQUS/Explicit, using the Johnson and Cook plasticity model. A strain rate-dependent, critical plastic strain fracture criterion was employed to model fracture. Good agreement is obtained between simulations and experiment and the model successfully captures the transitions in failure mode as projectile velocity increases. At velocities close to the ballistic limit, the plates fail by dishing and discing. As the incident velocity is increased, there are two transitions in failure mode, firstly to shear plugging and secondly to fragmentation and petalling. The simulations also show that, during the latter mode of failure, the kinetic energy of ejected debris is significant, and failure to include this contribution in the energy balance leads to a substantial over-estimate of the energy absorbed within the sheet. Information is also presented relating to the strain rates at which plastic deformation occurs within the sample under different conditions. These range up to about 105 s−1, with the corresponding strain rate hardening effect being quite substantial (factor of 2–3 increase in stress).International Journal of Impact Engineering.
Article: Predicting mesh-independent ballistic limits for heterogeneous targets by a nonlocal damage computational framework[show abstract] [hide abstract]
ABSTRACT: During highly dynamic and ballistic loading processes, large inelastic deformation associated with high strain rates leads, for a broad class of heterogeneous materials, to degradation and failure by localized damage and fracture. However, as soon as material failure dominates a deformation process, the material increasingly displays strain softening and the finite element predictions of ballistic response are considerably affected by the mesh size. This gives rise to non-physical description of the ballistic behavior and mesh-dependent ballistic limit velocities that may mislead the design of ballistic resistant materials. This paper is concerned with the development and numerical implementation of a coupled thermo-hypoelasto-viscoplastic and thermo-viscodamage constitutive model within the laws of thermodynamics in which an intrinsic material length scale parameter is incorporated through the nonlocal gradient-dependent damage approach. This model is intended for impact and ballistic penetration and perforation problems of heterogeneous metallic targets such as metal matrix composites with dispersed particles at decreasing microstructural length scales. An evolution equation for the material length scale as a function of the material microstructural features (e.g. mean grain size in polycrystalline materials or particle size and inter-particle spacing in metal matrix composites), course of plastic deformation, strain hardening, strain-rate hardening, and temperature is presented. It is shown through simulating plugging failure in ballistic penetration of high-strength steel targets of different thicknesses by a hard blunt projectile that the length scale parameter plays the role of a localization limiter allowing one to obtain meaningful values for the ballistic limit velocity independent of the finite element mesh density. It is also shown that a local damage model incorporating viscosity and heat conduction as localization limiters, which are known to implicitly introduce length scale parameters, is insufficient in illuminating the mesh sensitivity at impact velocities close to the ballistic limit and that the mesh sensitivity increases as the target thickness increases. Therefore, the proposed nonlocal damage model leads to an improvement in the modeling and numerical simulation of high velocity impact related problems.Composites Part B: Engineering.