Fragmentation of wedge loaded tempered structural glass

A high-speed study of tempered glass fracture propagation is presented. Tempered glass is used worldwide both architecturally and in the automotive industry, often playing a role in structural integrity. To accurately predict the brittle failure of the structural elements, it is essential to study crack initiation and formation. Cracks were initiated using a concentrated force employing a steel wedge. To capture abrupt crack propagation, digital high-speed photography was used with 50,000 frames per second and \(180\times 132\) pixels. A theoretical method based on fracture mechanics was developed and verified with experimental results. A correlation was found between the relative resistance of the specimens and the plate thickness. Which was explained by the difference in the tempered stress field between specimens. The fracture pattern close to the wedge started from a single crack which branched repeatedly after 0.6–0.8 cm, indicating a uniformly increasing energy release. Then using the governing fracture pattern and the stress field measured with a scattered light polariscope, a linear elastic fracture mechanics approach defined the energy release ratio. This parameter was found linearly dependent as a function of plate thickness. Applying this ratio as a known value, the fragment count standard (e.g. EN 12150-1:2000, Glass in building. Thermally toughened soda lime silicate safety glass. Definition and description, 2000) can be fine-tuned to be used not only for safety purposes but for thermal stress measurement as well. Thus, this could supplement the four point bending test [EN 1288-3:2000, Glass in building—determination of the bending strength of glass—Part 3: test with specimen supported at two points (four-point bending), 2000], where the effective tensile strength is measured only. Interestingly, the method developed could reduce overhead costs for companies by replacing the use of expensive machinery to measure stress in structural tempered glass elements.