Modeling and Simulation of Brittle Armors Under Impact and Blast Effects
Nordendale, Nikolas Andrew
One of the defense related research programs of recent interest is focused on developing ultra-high strength concrete (UHSC) mixtures and lightweight, rapidly deployable protective structures. A goal of these research programs is to develop protective options that depend more on system ductility or enhanced material properties to provide protection from bomb blast, shock and high-velocity projectile impact. One effort related to this involved developing a lightweight supporting structural system that could be rapidly constructed and positioned without heavy equipment or significant manpower while providing the required level of protection from specific threats by cladding it with multiple layers of thin UHSC panels. This research is concerned with modeling and simulation of such cementitious armor panels based on an accurate definition of its material characteristics through an appropriate material model reflecting the observed three-dimensional multi-scale behavior through actual tests on the material. The nature of high-velocity impact is a problem of high complexity requiring the proper definition of material model reflecting the equations of state, hydrostatic behavior, progressive damage, and strain-rate effects. In this research effort the focus has been on accurate prediction of the behavior of the cementitious armor panels by discrete numerical methods like finite element method (FEM) and smoothed particle hydrodynamics (SPH), devising appropriate material models and accurately characterizing the associated material parameters based on the tests undertaken for the purpose by a co-researcher at Army’s Engineering Research and Development Center. The primary purpose of this research is to simulate high-rate ballistic impact events of small, deformable projectiles on thin, UHSC armor panels as well as uniform blast loads on similar panel structures reinforced with randomly distributed and oriented reinforcing short fibers. This needed to be accomplished with a high degree of accuracy when compared to ballistic experiments. In this dissertation, the physics of these scenarios are described in detail, a literature survey of the most prominent material models used to simulate concrete under high-rate loading is described, a superior model for the applications in this research is described along with implementation details, parametric identification of the material model for two UHSCs is presented, strategies for both FEM and SPH methodologies are given along with strengths and weaknesses of both, numerical simulations of actual ballistic impact tests are presented to validate simulation results, and a multi-scale approach for homogenizing the properties of randomly distributed short-fiber reinforcement of UHSC is proposed and validated.