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Analytical Processes for Predicting Nanosecond Response of Highly Rate-Sensitive Materials


OBJECTIVE: Develop an analytical capability to predict the response, in nanosecond time intervals, of highly rate-sensitive materials to a ballistic or blast threat. DESCRIPTION: The protection of vital spaces on ships is a critical concern. Recent efforts utilizing low-cost glassy, highly rate-sensitive materials (e.g., conventional soda-lime glass, Plexiglas, and highly rate-sensitive polyurea and polyurethane polymers) to defeat ballistic and blast threats have been demonstrated. These materials exhibit strongly nonlinear, strain rate dependent behavior that can currently only be determined by costly and time-consuming test series. In order to rapidly design and evaluate different configurations of these materials, a modeling and simulation methodology is necessary to evaluate the trade space. The primary focus of this topic is to develop an analytical capability/method to predict the complex responses, in nanosecond time intervals, of these highly rate-sensitive materials when under stress. This predictive method should capture the transient levels of stability, support, and load transfer as well as the erosion characteristics and fracture and failure waves generated by armor penetrators such as hypervelocity jets and fragments. The predictive method should be capable of characterizing: shockwave propagations and interactions; the generation of failure waves; granulation/comminution; and, the erosive capability of conventional glass. For Plexiglas specifically, the predictive method should include fracture property transitions at high rates of loading (petalling to Hertzian failure) and the partitioning of energy and erosive capability. Additionally, high rate properties, rate-induced glass-transition, and phase change effects are of specific interest in predicting behavior in polyurea and polyurethane polymers. The predictive method will support the analysis of a layered structure of highly rate-sensitive materials with different thickness and component arrangements. It should be able to distinguish different thicknesses, placements, and orientation (obliquity of the threat) of these materials. It should also incorporate capabilities for energy loss from momentum trapping from failed components. The predictive method should include constitutive equations and Equation of State (EOS) in subroutines that can be readily utilized in existing computer programs such as ABACUS, AUTODYN, DYNA-S, LS-DYNA, and CTH or in Meshless and Particle methods. The predictive method should be capable of responding to threat weapons of interest. A sample weapon, a long-rod penetrator, will be provided by ONR to support the development of a predictive capability in Phase I. Later phases will include an Explosively Formed Projectile (EFP) and other shape charge threats. Optimized designs, derived for maximum protection against these various threats, will be required. PHASE I: Develop an analytical capability (i.e., subroutines) to predict, with nanosecond time resolution, the response of layered components of glass, Plexiglas, and polyuria/polyurethane to a ballistic or blast threat. The capability should incorporate: erosion/comminution, wave propagation/reflections, phase changes, fracture transitions, and momentum trapping. ONR will supply a long-rod penetrator for analytical purposes. PHASE II: Transition the analytical capability to an existing computer program such as ABACUS, AUTODYN, DYNA-S, LS-DYNA, and CTH or to Meshless and Particle methods. Perform blind design and optimization of targets to validate and verify the analysis against test data and actual EFP and shape charge threats test results supplied by ONR (some of this information may be classified). PHASE III: Upon successful Phase II completion, the company will support the transition of the technology to support the development of low-cost protection systems for a wide range of military, civilian, and space applications (e.g., protected vehicles, secure buildings, patrol craft, meteor and space debris impacts). PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: This SBIR may provide support to the design and acquisition community in the area of lightweight protective systems. This capability could have use in the development of low-cost protective systems for a wide range of military, civilian, and space applications (e. g., protected vehicles, secure buildings, patrol craft, meteor, and space debris impacts).
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