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Rheological Characterization of Next-Generation Ballistic Witness Materials for Body Armor Testing



Ran Tao, Kirk D. Rice, Aaron M. Forster, Randy A. Mrozek, Shawn T. Cole, Reygan M. Freeney, Anicet Djakeu Samen


Roma Plastilina No. 1 (RP1), a ballistic clay, is essential for establishing injury limits in standards-based ballistic resistance testing of body armor. It serves as a ballistic witness material (BWM), behind the armor, where the magnitude of plastic deformation in the clay after impact is the figure of merit. RP1 is known to exhibit complex thermomechanical behavior that requires temperature conditioning and continual calibration during usage. A less-complex BWM formulation with room-temperature capabilities and more consistent behavior is desired but validating only ballistic performance is extensive and expensive. A framework of lab-scale metrologies for repeatability, strain and strain rate sensitivity, and temperature dependence are needed to guide BWM development. The current work deals with rheological characterization of a candidate BWM material, i.e., silicone composite backing material (SCBM), to understand fundamental structure-property relationships in comparison to those of RP1. Small amplitude oscillatory shear frequency sweep experiments were performed at temperatures that range from 20 °C to 50 °C to map elastic and damping contributions in the linear elastic regime. Large amplitude oscillatory shear (LAOS) experiments were conducted in the non-linear region and material response is analyzed in the form of Lissajous curve representations with the values of perfect plastic dissipation ratio reported. The results show that SCBM exhibits dynamic properties that are similar in magnitude to those of temperature-conditioned RP1, but with minimal temperature sensitivity and weaker frequency dependence. Both SCBM and RP1 are identified as elastoviscoplastic materials at small and large strains, which is particularly important for accurate determination of back face deformation in body armor evaluation. The mechanical properties of SCBM show some degree of aging and work history effects. The results from this work demonstrate that the rheological


rheology, rubber process analyzer, mechanical properties, ballistic clay, backing material, body armor testing, LAOS, viscoplastic, viscoelastic, energy dissipation
Created March 14, 2019