the wagner group















STF ArmorTM

The central problem with the construction of any form of bodily armor is the determination of the balance between the weight/strength of the armor and the desired mobility. It is obvious that one would be able to cover up the body in heavy armor, similar to the knights of the Middle Ages, yet the immense weight and extra bulk would render the person immobile. Thus it is necessary to create armor that is as light and flexible as possible while keeping its strength intact. It is this problem that this project addresses.

The primary objective of body armor research is to develop a low cost, lightweight, wearable system with high ballistic performance. The composite material used in this study is composed of KEVLAR® weaves impregnated with a colloidal shear thickening fluid. KEVLAR® is a high performance fiber characterized by low density, high strength, and high energy absorption characteristics. The shear thickening fluids (STF's) are characterized by a significant, sometimes discontinuous increase in viscosity with increasing shear stress. Such fluids are composed of dense suspensions of colloidal particles. This shear thickening phenomenon can be utilized to enhance the ballistic protection afforded by fiber-based, flexible body armor. The objective is to demonstrate that the impregnated KEVLAR® is stronger (absorbs more energy at impact) than the untreated KEVLAR®.

Publications

N. J. Wagner and J. F. Brady, “Shear thickening in colloidal dispersions”, Physics Today, October 2009

M. J. Decker, C. J. Halbach, C. H. Nam, N. J. Wagner and E. D. Wetzel, "Stab resistance of shear thickening fluid (STF)-treated fabrics" Composites Science and Technology, accepted, August 2006

K. Kirkwood, J. Kirkwood, E. D. Wetzel, Y. S. Lee and N. J. Wagner, "Yarn pull-out as a mechanism for dissipating ballistic impact energy in Kevlar® KM-2 fabric - Part I: Quasi-static characterization of yarn pull-out" Textile Research Journal, 74(10), 920-928, Oct. 2004.

J. Kirkwood, Keith M. Kirkwood, Y. S. Lee, R. G. Egres, E. D. Wetzel and N. J. Wagner, "Yarn Pull-Out as a Mechanism for Dissipation of Ballistic Impact Energy in Kevlar®" KM-2 Fabric, Part II: Prediction of Ballistic Performance" Textile Research Journal, 74(11), 939-948, 2004

Y. S. Lee, E. D. Wetzel and N. J. Wagner, "The ballistic impact characteristics of Kevlar®-woven fabrics impregnated with a colloidal shear thickening fluid" J. Mat. Sci., 38(13) 2825-2833, 2003.