Clay composites as ballistic witness materials: time, temperature, and history dependent material properties
Jonathan E. Seppala, Chad R. Snyder, Kirk D. Rice, Gale A. Holmes
With the introduction of soft body armor in the 1970s, methods for certifying armor systems were also developed. Roma Plastilina Clay #1 (RP1) was chosen from several clay composites, foams, and gels and continues to be used as the ballistic witness material for back face deformation of soft body armor. Unfortunately, over the decades since RP1 was adopted, changes by the manufacturer to RP1 (brought about by pressure from other industries) have forced ballistics researchers to heat the composite to keep it within the specification developed in the 1970s. There is now a desire in the soft body armor testing community to replace the current material with new clay composites or other materials which do not require thermal treatment prior to use. To support that effort a proper and complete characterization of the material properties of RP1 is needed. Mechanical and thermal properties of RP1 were studied via small amplitude oscillatory shear (SAOS), large amplitude oscillatory shear (LAOS), and dynamic scanning calorimetry (DSC). Rheological characterizations of RP1 via SAOS have confirmed anecdotal experience by users, that the clay composite softens as it is "worked" and slowly stiffens as it rests. Using small strains the mechanical properties can be observed without perturbing the system (0.007% and 0.07% strain). Higher strains result in time dependent mechanical properties (0.7% strain) and recovery of mechanical properties can also be observed by applying the small strain post "working" of the material. Upon heating, the clay composite softens, prior work-history is erased, and the composite undergoes a melting transition. Continuing mechanical characterizations into the LAOS or non- linear region, RP1 is a shear thinning material (modulus decreases with increasing strain) at all measured temperatures and transitions from a transient network to a viscous liquid when melted. The culmination of these experiments indicates a material with a time, tempe
, Snyder, C.
, Rice, K.
and Holmes, G.
Clay composites as ballistic witness materials: time, temperature, and history dependent material properties, Personal Armor Systems Symposium 2014, Cambridge, -1, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=915532
(Accessed February 21, 2024)