Experimentally Investigating Annealed Glazing Response to Long-Duration Blast

Abstract

This paper investigates the response of annealed (float) glazing during long-duration blast as a function of glazing thickness, area, aspect ratio and edge support conditions. With positive phase durations in excess of 100ms, long-duration blasts produce substantial impulse and pronounced dynamic pressures. Transient dynamic response of annealed glazing during these events is a complex phenomenon dependent upon explosive proximity, structural arrangement and material properties. In particular, breakage time and initial fracture location are dictated by maximum principal stress exceedence at randomly distributed micro-flaws. As part of a larger research study, twelve full-scale air-blast trials employing 24 annealed glazing panels were conducted with ~14kPa peak static overpressure and ~110ms positive phase duration. Results are reported, where it is shown that notionally elastic edge supports can prevent glazing breakage versus rigidly clamped arrangements when suitable panel dimensions are employed. Fragmentation modes are also demonstrated to be a strong function of edge conditions with elastically supported panels producing large, angular fragments. In contrast, rigid arrangements are shown to induce localised impulsive stress transmission at clamped edges, leading to significant cracking and small fragments. Substantially different fragment masses and geometries demonstrate the need to accurately quantify edge supports when appraising fragment hazard. Quantification of peak panel deflection, breakage time and applied breakage impulse is then presented where results indicate the influence of edge supports and aspect ratio on glazing response to be dependent on proximity to the threshold area for a particular thickness.