GlasStress Ltd

Tallinn, Estonia

GlasStress Ltd

Tallinn, Estonia
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Anton J.,GlasStress Ltd | Errapart A.,Tallinn University of Technology | Paemurru M.,GlasStress Ltd | Lochegnies D.,University of Valenciennes and Hainaut‑Cambresis | And 2 more authors.
Estonian Journal of Engineering | Year: 2012

The paper shows that the residual stress at the surface of tempered glass panels may vary both locally (at a distance equal to the distance between the cooling jets) and globally, i.e., stresses near the edges and corners of the panels may be considerably different from the stresses in the middle part of the panels. That should be borne in mind while assessing the degree of temper by non-destructive measuring of the residual surface stress.


Aben H.,Tallinn University of Technology | Aben H.,Glasstress Ltd | Anton J.,Tallinn University of Technology | Anton J.,Glasstress Ltd | And 3 more authors.
Estonian Journal of Engineering | Year: 2013

It is shown that in tempered glass panels the edge stress and the thickness stress are closely related. Therefore the traditional edge stress measurement gives information also about the thickness stress and the surface stress. Thus for complete analysis of stresses near the edge of a glass panel only the edge stress measurement is needed.


Aben H.,Tallinn University of Technology | Aben H.,GlasStress Ltd | Anton J.,Tallinn University of Technology | Anton J.,GlasStress Ltd | And 6 more authors.
Estonian Journal of Engineering | Year: 2010

A portable scattered light polariscope SCALP has been developed, which permits measurement of the residual stress profile through the thickness of glass panels. At a glass factory strength assessment of glass panels of different thermal treatment was carried out using both residual stress measurement with SCALP and the traditional four-point bending tests. Linear correlation between the residual surface stress and the bending strength was observed. At another glass factory residual stress in glass panels was measured before performing the traditional fragmentation test. The results of the fragmentation test were extremely scattered and had almost no correlation with the values of the residual stress. It is concluded that sufficiently reliable assessment of the strength of glass panels is obtained by measuring the residual stress at the surface.


Aben H.,Tallinn University of Technology | Lochegnies D.,University of Valenciennes and Hainaut‑Cambresis | Chen Y.,University of Valenciennes and Hainaut‑Cambresis | Anton J.,Tallinn University of Technology | And 2 more authors.
Experimental Mechanics | Year: 2015

An important characteristic of glass panels is residual stress, especially stress at the surface. To measure this stress different devices have been developed, which use either the tunneling effect in light propagation near the surface or the scattered light method. Both devices are rather expensive. At the same time, many glass manufacturers use measurement of the stress at the edge of the panel. This measurement can be carried out with traditional methods of 2D photoelasticity. However, until now the data of edge stress measurement has not been used to the full extent. The edge stress itself is an estimation of the degree of temper of the panel. Besides, the region, where average through thickness stress is tensile, can be found. However, real stress distribution in the panel can not be determined. In this paper we show that since the edge stress and surface stress are in correlation, the edge stress permits to estimate also the value of the surface stress. Experimentally and with mathematical modelling of the tempering process it has been shown that practically edge stress equals the surface stress. Knowing the surface stress, it is possible to determine distribution of the parabolic tempering stresses through the panel thickness. That permits also to determine real stress field in the so-called tensile stress area. Thus complete analysis of residual stresses near the edge of the panel can be carried out. © 2014, Society for Experimental Mechanics.


Hodemann S.,University of Tartu | Valdmann A.,University of Tartu | Anton J.,GlasStress Ltd | Anton J.,Tallinn University of Technology | Murata T.,Nippon Electrical Glass Co.
Journal of Materials Science | Year: 2016

A new non-destructive gradient scattered light method is presented for micron-scale stress profile measurement in chemically strengthened (chemically tempered, ion exchanged) glass. Direct non-destructive stress measurement in the surface layer (<100 µm) of chemically strengthened glass is reported for the first time. This is accomplished by passing a narrow laser beam through the surface layer of the glass at a considerably large incidence angle of 81.9°. The theory of gradient scattered light method is based on the ray tracing of ordinary and extraordinary rays in chemically strengthened glass and calculating the optical retardation distribution along the curved ray path. The experimental approach relies on recording the scattered light intensity and calculating the optical retardation distribution from it. The stress profile is measured in a chemically strengthened (8 h at 480 °C in a salt mixture of 80 mol% KNO3 and 20 mol% NaNO3) lithium aluminosilicate glass plate to illustrate the capability of the method. Measured surface compressive stress was −1053 MPa and case depth 365 µm. Method is validated with transmission photoelasticity. The method could also be used for stress profile measurement in all transparent flat materials (such as very thin thermally tempered glass slabs or polymers). Additional new applications could be: (1) enhanced version of Bradshaw’s surface layer etching method for stress profile measurement in case of ultra-thin case depths <20 µm; (2) micron-scale non-destructive tomography of layered polymeric gradient-refractive-index materials. The experimental procedure is developed to the level of full automation and the measurement time is less than 10 s. © 2016 Springer Science+Business Media New York


Hodemann S.,University of Tartu | Mols P.,University of Tartu | Kikas J.,University of Tartu | Anton J.,GlasStress Ltd
Glass Technology: European Journal of Glass Science and Technology Part A | Year: 2014

Scattered light fringe patterns are measured in thermally tempered and annealed glass plates to determine the residual stress profile through the glass thickness. Numerically generated fringe patterns are compared with experimental ones. Stress profiles calculated from experimental fringe patterns are compared with stress profiles measured with a scattered light polariscope (SCALP).

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