Computational Modeling of Failure Patterns of Glass Panels with Imperfections Subjected to Air Blast

Hossein Ataei; James C. Anderson
Glass fragments are a prime source of injury to occupants of buildings subjected to explosive events during which window glass breaks into either flying shards (annealed glass windows) or fragments (fully tempered glass). These account for injuries ranging from minor cuts to severe wounds. A successful blast-resistant glazing design requires balancing of the safety and security of the window panels with physical appearance and cost-effectiveness. Moreover, it should consider the principles of a reasonable degree of protection against explosive threats based on the proposed level of security and previous lessons learned. In this paper, explicit finite element method (FEM) with is used for modeling the window failure and investigate the failure patterns of annealed and fully tempered glass windows panels with embedded imperfections across the panel. For this purpose, the element-removal technique is utilized in accordance with the fracture micromechanics' principles and the brittle failure criteria of displacements; strains and stresses. The results of the analysis demonstrate that the response of the conventionally-framed window panels to blast loading cases depends upon the glazing technologies; blast load intensities; the glass types; and the location of imperfections. Through the application of element removal technique and stress redistributions at each infinitesimal time increment, the results of this paper further demonstrates that the existence of glass imperfections in the window panels will make them more vulnerable against the air blast overpressures for both annealed and fully-tempered glass panel cases: For fully tempered glass panels, the vulnerability arises from greater stress concentrations at the location of glass defects as well as higher brittleness of the panel itself when compared to the annealed glass panels. The results of this study show that the existence of defects along the edges will help in redistribution of the stresses in a way that the yield lines will pass through these imperfection locations. The general failure pattern for defective annealed glass panels subjected to small intensity air blast will be very similar to the failure pattern of homogeneous window panels yet with a faster pace. However, when subjected to a higher intensity air blast, the severity of the load will cause excessive rotation angles in the panel and subsequent computational divergence and instability. The panel failure will occur much faster and with different patterns compared to the case of annealed glass panels subjected to smaller intensity air blasts.
Glass; Air Blast; Safety; Window Panels; Fracture Mechanics; Crack Propagation
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