The Fracture Process of Tempered Soda-Lime-Silica Glass

Abstract

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.

Remaining stress-state and strain-energy in tempered glass fragments

“…This is verified by the fact that the fracture propagated in the tensile region first and then in the compressive layer over a period of time". However, in more recent work, (Nielsen et al 2009;Dugnani et al 2014) it is shown experimentally and analytically that the surface regions are cracking (almost) simultaneously with the center part. It is therefore decided, in the present work, to investigate the total strain energy in a fragment.…”

“…Some authors, (Barsom 1968;Nielsen et al 2009), have drilled with diamond tipped drills into the tensile zone, in order to minimize the energy added to the system. In these cases, it is reasonable to assume, that only the stored strain energy, from the residual stresses, are driving the fragmentation.…”

Deformations and strain energy in fragments of tempered glass: experimental and numerical investigation

“…1 The sudden release of strain energy will cause the glass to fragmenting at such high speed, that the fragments are accelerated and, if not hindered, they will move in an explosive manner, see e.g. Nielsen et al (2009). There are primarily in-plane residual stresses in the tempered glass, the displacement of the glass fragments will therefore only be in the plane of the glass plate, Fig.…”

“…Gulati applies the analytical model developed by Barsom (1968) to estimate the same frac-tion and finds that 35% of the initial strain energy is used. Nielsen et al (2009) presents a study of the fracture process of tempered glass. The fracture process is initiated with a diamond drill to transfer a minimum of energy to the test specimens.…”

“…The model is based on a linear elastic finite element model. On the basis of more recent studies Nielsen et al (2009), the author of the article suggests that it is more reasonable to apply the total strain energy of the tempered glass. From the study it is clearly shown that the initial stress state changes from being plane hydrostatic to becoming fully three dimensional in the fragment.…”