Influence of moisture and thermal cycling on delamination flaws in transparent armor materials: Thermoplastic polyurethane bonded glass-polycarbonate laminates

Abstract

Transparent armor laminates (TALs), manufactured from layers of soda-lime-silica float glass, thermoplastic polyurethane, and polycarbonate, are known to suffer unpredictable delamination in ambient-condition service, interfering with their transparency and reducing operational lifespan. The nature of the mechanisms leading to delamination are not well known, and believed to be driven by exposure to moisture, thermal cycling, and stresses induced by differing thermal expansion of the layers. Herein, small-scale coupons of TAL laminates were hygrothermally aged for a variety of durations and moisture exposure geometries, then thermally cycled to investigate the onset of delamination. As duration of aging was increased, the mode of failure changed from cohesive void formation at high temperature (85 °C), to interfacial crack during less-extreme thermal cycling (0 °C to 70 °C). The progression indicated that the barrier to nucleating delaminations reduced with progressing moisture exposure, leading to less-selective initiation and increasingly contiguous growth of the delaminations. In this study, for the first time, delaminations were successfully and consistently produced in glass-polycarbonate laminates, the delamination failure mode was correlated with the degree of moisture exposure, and both a theoretical basis to guide further studies and a methodology to assess the delamination resistance of current and future transparent armor designs are suggested.