Ballistic limit evolution of field-aged flexible multi-ply UHMWPE-based composite armour inserts

The development of high-performance polymer-based fibres has given rise to new generations of ballistic protection. However, as polymers and their composites are sensitive to ageing, it is important to understand how these armours maintain their protective capabilities over time. This paper focuses on two sets of armour panels consisting of 36 plies of DYNEEMA® SB21. The 'aged' samples, were collected after ten years of regular use in the field, while the equivalent 'new' samples were manufactured specifically for this study. A large number of ballistic impacts were performed using fragment simulating projectiles to determine differences in ballistic limit. In addition, the number of perforated plies was recorded for non-perforations, while residual velocities were assessed for perforations using a high-speed camera. Overall, the ballistic performance of the samples did not appear to change significantly over time. Nevertheless, the statistics show that 'aged' specimens have slightly more dispersion at their ballistic limit and absorb slightly more kinetic energy than 'new' specimens. Apparently, the ageing of this protection was responsible for the oxidation of the composite material and a partial adhesion between the plies, which explains the small differences in the evaluated ballistic limit quantifiers.