This work presents experimental observations of the characteristic fracture process of tempered glass. Square specimens with a side length of 300 mm, various thicknesses and a residual stress state characterized by photoelastic measurements were used. Fracture was initiated using a 2.5 mm diamond drill and the fragmentation process was captured using High-Speed digital cameras. From the images, the average speed of the fracture front propagation was determined within an accuracy of 1.0%. Two characteristic fragments were found to form on each side of the initiation point and are named "Whirl-fragments" referring to the way they are generated. An earlier estimation of the inplane shape of the fracture front is corrected and a hypothesis on the development for the fracture front is offered. The hypothesis is supported by investigations of the fragments using a Scanning Electron Microscope (SEM) which also revealed a micro scale crack bridging effect.

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Abstract. The mechanical response of post-tensioned glass beams is explored in this paper. This is done through bending experiments on post-tensioned glass beam specimens with either mechanically anchored or adhesively bonded steel tendons by which a beneficial pre-stress is inflicted on the glass beams. In addition, reference beams with identical geometry but without tendons are tested. From the results of the bending experiments it can be seen that the post-tensioned glass beams reach higher initial fracture loads than the reference glass beams. Furthermore, the post-tensioned glass beams develop a significant post-fracture reserve. From this it is concluded that post-tensioning a glass beam is a feasible concept, which provides increased initial fracture strength and enhanced post-fracture performance.

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When tempered glass breaks, it shatters into relatively small pieces depending on the residual stress state in the glass. This has been known for centuries and is currently used in standards for classifying whether a piece of glass is tempered or not. However, the process of fragmentation is complex and only a few, relatively simple, models have been suggested for predicting the fragment size. The full theoretical explanation is still to be found and this work aims at providing another brick to the puzzle. The strain-energy present in tempered glass is obviously contributing to the fragmentation process and some authors e.g. Barsom (J Am Ceram Soc 51 (2) The present paper applies a quasi-static finite element model in order to answer these questions. In the present paper an example on the deformation and the stress redistribution in a fragment is given. Furthermore, a parametric investigation on the strain energy remaining in cylindrical-and prismatic fragments is given. It is shown, that there exists a simple relation between the thickness of the glass pane and the remaining strain energy in the fragment. A simple method for estimating the remaining strain energy in a fragment of a given shape and initial residual stress state is presented.