Residual stress determination in chemically strengthened and thermally tempered glass plates using scattered light method
Date
2019-01-31
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Abstract
Arendati välja konfokaalmikroskoopial ja hajunud valguse meetodil põhinev
optiline meetod jääkpingete sügavusprofiili mõõtmiseks keemiliselt karastatud
klaasis. Konfokaalmikroskoopia võimaldab väga suure ruumilise lahutusega
tomograafiliselt sondeerida Rayleigh hajunud valguse intensiivsuse jaotust ja
sellest arvutada jääkpingete profiil karastatud klaasis.
Teine metoodika, mida kasutati pingeprofiilide mõõtmiseks keemiliselt karastatud
klaasis põhines klaasplaadile hajunud valguse meetodil kus pealelangev
valgus oli kaldu uuritava klaasplaadiga. Selle metoodika jaoks arendati välja
valguse paindumise mõju eemaldav iteratiivne algoritm. Algoritmi testimisel
leiti, et selle konvergeerumiskiirus sõltus sellest kas klaasi pinnal olid surve- või
tõmbepinged.
Olulise tulemusena näidati, et simulatsioonides valguse paindumise mõju
edukalt eemaldav algoritm toimis ka eksperimentaalsete pingeprofiilide peal.
Selle kinnituseks oli survepingete ja tõmbepingete vahelise tasakaalu oluline
paranemine optilise käiguvahe jaotusest arvutatud pingeprofiilis. Välja
arendatud algoritm on seega piisavalt testitud, et kasutada seda Eesti firma
GlasStress OÜ poolt toodetavas polariskoobis SCALP-05.
Samuti näidati termiliselt karastatud klaasplaatide pinnasurvepingete (mõõtes
selle hajunud valguse meetodil) ja purustamispinge vahelist lineaarset korrelatsiooni. Sama metoodikaga uuriti ka pingete ebaühtlust termiliselt karastatud
klaasides. Näidati, et pinnapinged erinevad oluliselt sõltuvalt uuritavast asukohast.
A new optical method for evaluation of the stress profile in chemically strengthened glass based on confocal detection of the scattered laser beam is presented. Confocal microscopy allows scanning within the light beam and collecting Rayleigh-scattered light from a microscopic volume. Estonian company GlasStress Ltd produces SCAttered Light Polariscope SCALP-05 which is a unique device in the world that determines the strength of tempered glass (for example, Gorilla glass used on phone screens, tempered window glasses, sauna doors) very quickly and without damage to the glass. For this purpose, the apparatus is placed on a glass with a super-thin layer of oil, the strength of which is known. SCALP, which uses photoelasticity of scattered light, responds to glass strength in four seconds. The developed algorithm eliminates the influence of light ray bending in the makes the measurement result up to ~25% more accurate. A linear correlation was found between surface compression measured with oblique incidence scattered light method and breaking strength measured with traditional four-point bending tests. Stress inhomogeneity was also investigated. It has been shown that surface compression of thermally 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 differ significantly from the stresses in the middle part of the panels.
A new optical method for evaluation of the stress profile in chemically strengthened glass based on confocal detection of the scattered laser beam is presented. Confocal microscopy allows scanning within the light beam and collecting Rayleigh-scattered light from a microscopic volume. Estonian company GlasStress Ltd produces SCAttered Light Polariscope SCALP-05 which is a unique device in the world that determines the strength of tempered glass (for example, Gorilla glass used on phone screens, tempered window glasses, sauna doors) very quickly and without damage to the glass. For this purpose, the apparatus is placed on a glass with a super-thin layer of oil, the strength of which is known. SCALP, which uses photoelasticity of scattered light, responds to glass strength in four seconds. The developed algorithm eliminates the influence of light ray bending in the makes the measurement result up to ~25% more accurate. A linear correlation was found between surface compression measured with oblique incidence scattered light method and breaking strength measured with traditional four-point bending tests. Stress inhomogeneity was also investigated. It has been shown that surface compression of thermally 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 differ significantly from the stresses in the middle part of the panels.
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Väitekirja elektrooniline versioon ei sisalda publikatsioone
Keywords
stress (mechanics), measurement methods, plates