Abstract:
"Selected Aspects Of Numerical Analysis Of Layered Flexible Structures Subjected To Impact Of Soft Core Projectile"
This study identifies and discusses critical aspects of using the finite element method for the analysis of a soft-core projectile impacting a layered, flexible ballistic package on a plastic backing. The investigation was conducted by developing a finite element model in LS-Dyna to simulate the normal impact of a 7.62 mm TT projectile into a target composed of 36 plies of Dyneema SB71. The finite element analysis highlighted a primary challenge: the standard Lagrangian material description, common in solid mechanics, fails to accommodate the extreme deformations experienced by the projectile's soft lead core and the plastic backing during the impact event. To address this limitation, the study employed an R-adaptive finite element method, a technique that cyclically rebuilds the numerical mesh for the severely deforming components—in this case, the projectile core and the backing material. The finite element simulations demonstrated that this adaptive method is necessary to successfully model the projectile's mushrooming and the formation of a depression in the backing without premature calculation failure. However, the analysis also revealed a significant negative side effect of the R-adaptive technique: a progressive loss of mass was observed in the remeshed parts throughout the simulation, which was reflected in the model's global energy balance. The paper concludes that while the R-adaptive finite element method is a necessary tool for obtaining a solution in this class of problems, it must be applied with considerable care, as the frequency of mesh rebuilding and the minimum permissible element size must be carefully controlled to keep the associated mass loss at an acceptable level.
