Testing of Bomb Resistant Glazing Systems: Experimental Investigation of the Time Dependent Deflection of Blast Loaded 7.5 mm Laminated Glass

Caroline Kranzer, Gerhard Gürke & Christoph Mayrhofer, Fraunhofer Institute for High-Speed Dynamics, Ernst

A laser optical displacement measurement technique allows to study the displacement of window glass loaded by explosive blast. Preliminary tests were done with the Fraunhofer EMI shock tube facility and with small high explosive (HE) charges at free field situations. Detailed deflection versus time histories are available for 7.5 mm laminated glass panes with an area of 0.8 square meter. The panes were firmly fixed in deep rebates. The experimental results indicate that there exists a critical blast impulse above which the panes are damaged if such impulse is received within a minimum or critical time. The critical time was identified as one-quarter of the natural period of oscillation. The Break Safely (B/S) / No Hazard level of damage, at which the pane just ‘cracks’, was reached if approximately 70 Pa*s to 80 Pa*s of blast impulse were applied within the critical time. For the small high explosive tests the blast duration was shorter than the critical time. In this case the response of the pane is directly proportional to the value of the blast impulse. Also the results of the shock tube tests fit into the concept of ‘critical impulse in a critical time’, a hypothesis proposed many years ago. A measurable criterion to characterize the B/S level of damage can help to validate numerical calculations of window glass breakage.

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The Authors

Ms. Caroline Kranzer MEng. Fraunhofer Institut Kurzzeitdynamik, Ernst-Mach-Institut Dipl.-Ing. (FH) MEng Caroline Kranzer works for the Fraunhofer Institute for High-Speed Dynamics, Ernst-Mach-Institut in Efringen-Kirchen, Germany. She has been a scientist in the department Safety Te... Read more