Esmaspäeval, 7. jaanuaril 2019 kell 14.15 toimub Physicumis W.Ostwaldi 1 seminariruumis D312
Laserspektroskoopia seminar No 266
Esineb Siim Hödemann , TÜ FI laserspektroskoopia labor
Residual stress determination in chemically strengthened and thermally tempered glass plates using scattered light method (Doktoritöö materjalid)
The main result of the thesis was the development of a new confocal microscopy method for measuring the residual stress profile of chemically strengthened glass, an algorithm to remove the influence of light ray bending from stress profiles measured using oblique scattered light method. Also the relationship between strengthened glass surface compression and breaking stress was investigated.
Confocal microscopy (Fig 1) allows to scan inside the light beam and to collect Rayleigh-scattered light from a microscopic volume. A schematic depiction of the stress measurement method based on confocal microscopy is shown in Fig 2.
Estonian company GlasStress Ltd produces SCAttered Light Polariscope SCALP which is a unique device in the world that determines the stress profile of tempered glass (for example, Gorilla glass used on phone screens, tempered window glasses, sauna doors) very quickly and without damage to the glass. The developed algorithm eliminates the influence of light ray bending in the makes the measurement result 10-20% more accurate.
In addition, the relationship between the surface compressive stress of the glass and the breaking stresses was also identified. It was concluded that the European standardized glass strength determination test so far used should be replaced by a substantially more accurate non-destructive measurement technique using a SCALP polariscope.
Fig1: Basis of confocal microscope, invented by Marvin Minsky
Fig2: Set-up of confocal scattered light method for stress profile measurement in chemically strengthened glass.