The effect of temperature on the impact behaviour of glass/polycarbonate laminates

A systematic investigation has been performed into the mechanisms that lead to spall of bullet-proof glass/polycarbonate laminate constructions at low temperatures. A range of techniques were deployed including liquid jet impact, high speed photography, and a light gas gun. Spall formation was shown to take ca. ten times longer than a simple shock-wave overlap mechanism would imply. However, a number of experimental observations including the radii of fracture bands in the glass and fractographic examination of the edge of the polycarbonate spalls led us to consider a more complex elastic wave analysis: the reinforcement of Rayleigh surface waves by tensile elastic waves reflected from the various boundaries within the laminate. This predicted that the radius of the spall should be proportional to the thickness of the front glass layer. Comparison with the results of full-scale tests confirmed that this was indeed the case.