Gradient scattered light method for non-destructive stress profile determination in chemically strengthened glass

Abstract

A new non-destructive gradient scattered light method is presented for micronscale stress profile measurement in chemically strengthened (chemically tempered, ion exchanged) glass. Direct non-destructive stress measurement in the surface layer (\100 lm) 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% KNO 3 and 20 mol% NaNO 3 ) lithium aluminosilicate glass plate to illustrate the capability of the method. Measured surface compressive stress was -1053 MPa and case depth 365 lm. 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 lm;(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.

Measurement of stress build‐up of ion exchange strengthened lithium aluminosilicate glass

“…An important question here is whether the SRI or CRI algorithms produce stress reconstruction errors, that are smaller than experimental errors. From our previous report, the precision of SCALP‐05 is ±3.7% for stresses >20 MPa. Figure A illustrates that the maximum value of SRI equilibrium error is 15% and the corresponding surface stress reconstruction error of SRI is 18%.…”

“…The purities of both KNO 3 (Otsuka Chemical Co., Ltd.) and NaNO 3 (Kanto Chemical Co., Ltd.) were >99%. The stress‐optic coefficient was C = 3.3 Brewster (1 Brewster = 10 −6 MPa −1 ).The detailed description of finding the value of C is given in our previous report . The glass composition in Table was determined experimentally using energy‐dispersive X‐ray (EDX) microanalysis.…”

A study on ion‐exchanged, soda‐lime glass’s residual stress relationship with K+/Na+ concentration

“…In the proposed approaches, the material behavior was inferred directly from ion‐exchanged SLG rather than from “as‐melted” samples since the latter had been shown to display different properties than ion‐exchanged glasses . Moreover several mature and relatively accurate techniques exist to measure residual stress profiles in ion‐exchanged SLG …”

Spontaneous Fracture in Thermally Strengthened Glass - A Review and Outlook

“…The method is slightly better than ultrasonic because it is possible to make a better estimation of the size of the inclusion. Laser imaging is similar to the scattered light method that is employed to analyze stresses in strengthened glass [103,104]. Scattered light method has also been tested for identifying NiS inclusions in glass [105], out of 1135 tested glass sheets could 17 defects larger than 60 µm be found.…”