Synthesis and Ballistic Evaluation of Selected Transparent Polyurethane Block Copolymers, Part 4: Effects of Environmental Factors Upon Ballistic Response
ARMY MATERIALS AND MECHANICS RESEARCH CENTER WATERTOWN MA
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Investigation has been continued of polyurethane block copolymers for possible application as transparent armor. For a typical formulation, the V50 ballistic limit velocity exhibited a maximum at room temperature, with lower values at -50 F and 175 F. Aging at ambient conditions tended to decrease the brittleness and raise the V50 of these polymers. High values of relative humidity led to softening and ductile response of brittle formulations. Immediate desiccation of brittle formulations caused retention of hardness and brittleness, whereas after prior humidification, desiccation removed much water but did not reverse the prior transition to ductile ballistic response. Incorporation of selected additives had little effect upon the properties of these polymers. Exposure produced changes in weight and hardness which may correlate with humidities and weathering processes the corresponding changes in V50 were small and not directly related to these other changes.