Failures of certified soft body armor led to a call to understand the underlying mechanisms of the failure. Research has indicated that the folding of ballistic fibers comprising the soft body armor may be a factor in the performance deterioration that has been observed. To quantify the impact of this mechanism, an apparatus was designed and built to simulate the folding that may occur to the ballistic fibers while the vest is in use. This device systematically folds woven fabric and yarns of ballistic fibers to assess the impact of folding on ballistic fiber properties. After cycling a piece of woven poly(benzoxazole) (PBO) fabric for 80,000 cycles, a 41 % reduction in the ultimate tensile strength and strain to failure of the PBO fibers was observed. These results were also reflected in data obtained from small angle X-ray scattering where the long range order of the fiber structure is changed by the folding process. Preliminary failure analysis using scanning electron microscopy on tested fibers also revealed changes in failure morphology.
SAXS, SEM, fatigue life, fiber strength, ballistic fibers, single fiber testing