A detailed investigation of the mechanical properties of polybenzoxazole fibers within soft body armor.

Using the modified-single fiber test developed by Holmes and colleagues (J Appl Polym ), a detailed analysis of fibers extracted from soft body armor comprised of polybenzoxazole (PBO) fibers was performed. The data indicate that hydrolytic degradation of these ballistic fibers is accompanied by degradation associated with folding (or fatigue-induced degradation) and an undefined degradation mechanism associated with vest use that appears to target the horizontal yarns of the alternating 0°/90° woven layers. These additional failure mechanisms have the potential to create localized regions in the PBO soft body armor which are significantly lower than the homogeneous degradation expected from uniform hydrolysis. Results also indicate that the absence of ballistic penetrations in the initial study conducted at the National Institute of Standards and Technology may be associated with using the properties of the fibers from the back panel of a compromised vest as representative of the properties in the front panel that was penetrated. Analysis of a field return vest showed the front panel to be significantly more degraded than the back panel. [ABSTRACT FROM AUTHOR]