Penetrator Case Fracture Predictive Technology: Volume 2-Numerical Algorithms and Computations

The objective of this work was to develop the capability to perform 3D crack propagation computations for penetrator cases during impact and penetration into hard concrete targets. The first step was to develop a new 2D algorithm that did not require rezoning (as rezoning would be very complex in 3D geometry), the second step was to extend the new technique to 3D geometry, and the third step was to apply the 3D algorithm to actual hard target penetrator impact events. The numerical algorithms described in this report have been incorporated into the 1999 version of the EPIC code. A finite element algorithm is presented for dynamic crack calculations in general directions. The algorithm avoids node splitting and the associated remeshing and redefinition of contact surfaces. and does not rely on failure mechanisms embedded in the constitutive model. The T* energy integral is employed as the dynamic fracture parameter, guiding the crack tip through the mesh. Elements through which the crack tip passes lose the ability to sustain deviatoric and tensile volumetric Stresses, and their interfaces with the nest of the mesh model fractured surfaces that can sustain only compressive normal tractions (when the crack is closed). This technique is therefore referred to as the element failure algorithm.
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