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Research Papers: Design and Analysis

Semi-Infinite Target Penetration by Ogive-Nose Penetrators: ALEGRA/SHISM Code Predictions for Ideal and Nonideal Impacts

[+] Author and Article Information
Joseph E. Bishop

 Sandia National Laboratories, Albuquerque, NM 87185-0378jebisho@sandia.gov

Thomas E. Voth

 Sandia National Laboratories, Albuquerque, NM 87185-0378tevoth@sandia.gov

Note that the definition of AOA given in Fig. 1 must be generalized to include both pitch (rotation of penetrator about z-axis) and yaw (rotation of penetrator about y-axis) for impact problems that do not possess a plane of symmetry. All of the numerical results presented in this paper possess a plane of symmetry.

J. Pressure Vessel Technol 131(1), 011205 (Nov 24, 2008) (7 pages) doi:10.1115/1.3013859 History: Received December 14, 2005; Revised January 21, 2008; Published November 24, 2008

The physics of ballistic penetration mechanics is of great interest in penetrator and countermeasure design. The phenomenology associated with these events can be quite complex, and a significant number of studies have been conducted ranging from purely experimental to “engineering” models based on empirical and/or analytical descriptions to fully coupled penetrator/target, thermomechanical numerical simulations. Until recently, however, there appears to be a paucity of numerical studies considering “nonideal” impacts (Goldsmith, 1999, “Non-Ideal Projectile Impact on Targets  ,” Int. J. Impact Eng., 22, pp. 95–395). The goal of this work is to demonstrate the SHISM algorithm implemented in the ALEGRA multimaterial arbitrary Lagrangian Eulerian code (Boucheron, , 2002, ALEGRA: User Input and Physics Descriptions, Version 4.2, SAND2002-2775, Sandia National Laboratories, Albuquerque, NM). The SHISM algorithm models the three-dimensional continuum solid mechanics response of the target and penetrator in a fully coupled manner. This capability allows for the study of nonideal impacts (e.g., pitch, yaw, and/or obliquity of the target/penetrator pair). In this work predictions using the SHISM algorithm are compared with previously published experimental results for selected ideal and nonideal impacts of metal penetrator-target pairs. These results show good agreement between predicted and measured maximum depths-of-penetration (DOPs), for ogive-nose penetrators with striking velocities in the 0.5–1.5 km/s range. Ideal impact simulations demonstrate convergence in predicted DOP for the velocity range considered. A theory is advanced to explain disagreement between predicted and measured DOPs at higher striking velocities. This theory postulates uncertainties in angle-of-attack for the observed discrepancies. It is noted that material models and associated parameters used here were unmodified from those in literature. Hence, no tuning of models was performed to match experimental data.

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Figures

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Figure 1

Schematic defining penetrator angle-of-attack (AOA) and angle-of-obliquity (AOO)

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Figure 2

Computational algorithm for the ALEGRA code

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Figure 3

An example ALEGRA/SHISM mesh. The Lagrangian penetrator mesh is highlighted in red while the ALE/Eulerian target-region mesh is white. The inserted target material is shown in gray. The Lagrangian contact interface joins the two regions.

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Figure 4

The ogive-nose penetrator geometry

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Figure 5

Predicted and experimental (15) DOPs for normal impact. Results are plotted as a function of striking velocity for various levels of mesh refinement.

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Figure 6

Final mesh (Ogive-2) following a normal impact with striking velocity Vs=570 m/s. The penetrator mesh has been removed for clarity.

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Figure 7

Final mesh (Ogive-2) following a normal impact with striking velocity Vs=966 m/s. The penetrator mesh has been removed for clarity.

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Figure 8

Final mesh (Ogive-2) following a normal impact with striking velocity Vs=1770 m/s. The penetrator mesh has been removed for clarity.

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Figure 9

Final mesh (Ogive-2) following a normal impact at a striking velocity of Vs=1580 m/s with a 2 deg angle-of-attack. (The legend refers to the equivalent plastic strain contoured on the penetrator.)

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Figure 10

Estimated error in predicted DOP as a function of mesh refinement, h, for three striking velocities. Rates of convergence for predicted DOP are also shown.

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Figure 11

Percent error in predicted DOP as a function of mesh refinement, h, for three striking velocities. The estimated error in DOP is normalized by the estimated value of DOPexact.

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Figure 12

Comparison of predicted and experimental (6) 15 deg oblique impact DOP as a function of striking velocity for the ogive-nose penetrator using an Ogive-2 mesh

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Figure 13

Final mesh (Ogive-2) following a 15 deg oblique impact at a striking velocity of Vs=1209 m/s

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Figure 14

Final mesh (Ogive-2) following a 45 deg oblique impact at a striking velocity of Vs=553 m/s. (The legend refers to the equivalent plastic strain contoured on the penetrator.)

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