This study is part of a research program which aims to develop a laminated glass windshield whose laceration potential is very weak and even almost nonexistent. Two types of new safety windshields are tested. They differ only by the strengthening level of the V.H.R. glass which is used. In both cases, the very thin 0.050 in. (1.2 mm) thick inner sheet and the 0.110 in. (2.8 mm) thick outer sheet are made of V.H.R. glass. Nevertheless, the glass of the outer ply has a deliberately limited tensile strength. The polyvinylbutyral plastic interlayer is 0.030 in. (0.76 mm) thick. The evaluation of the biomechanical behaviour of these windshields is made in different ways, among them a laboratory study which includes impact tests with a headform free falling on positioned samples. During the impact, all measures defining the safety performance are recorded at high speed: the deceleration peak along two orthogonal axes, the resultant severity index relating to the initial impact and to the plow-in, the tearing length of the plastic interlayer, and finally the laceration potential is evaluated on a laceration rating scale used by Prof. Patrick at the Wayne State University. A laceration index is given following the number and size of the cuts measured on the two superposed chamois leathers covering the headform. The experimental parameters particularly studied are: temperature, impact velocity, impact location, increase of the mechanical strength of the sheets. The new safety reinforced laminated windshield, whose laceration potential is very low and nonexistent at very high impact energy, might be used as a true passive restraint system if the tensile strengths of the reinforced glass are adjusted.
Abstract