GB/T 18144-2008Test method for measurement of stress in glass (English PDF)

4.1 Surface stress measurement

4.1.1 Measurement principle

The testing principle of surface stress meter is to use optical waveguide effect of the tin

diffusion layer on the surface of float glass to measure. The scattered light, emitted from a

light source (incandescent light bulb) and through a slit, turns into parallel light after being

converged by cylindrical prism of a high refractive index.

4.1.2 Reagents for test

Refraction oil. Its refractive index shall be greater than the glass but not greater than the

instrument prism. Refraction oil shall not have a corrosive effect on the instruments.

4.1.4 Preparation and preservation of sample

Use finished products as the sample. If there is coating on the surface of the tin diffusion

layer of the sample (such as curtain wall glass, glaze coating of car's back windshield

glass), use hydrofluoric acid or abrasive cloth to remove it. And take the area where the

coating is removed as the stress testing point of the sample. In order to avoid the

generation of thermal stress, the temperature inside and outside the sample must be

consistent and same as the ambient temperature.

4.1.6 Test procedures

a) The tin diffusion layer of the sample to be measured shall be placed upwards and

horizontally at a stable state;

b) Wipe and clean the glass surface. And drop 1 ~ 2 drops of refraction oil on the

testing point;

c) Make the instrument prism parts to contact with the measuring points reliably;

d) Adjust the light source position, the slit position and the retro-reflector angle to

ensure a clear image with light-shade stairs appear in the observation field;

e) Use the micrometer eyepiece to read the height of the stair d, accurate to 0.01 mm;

f) Compressive stress and tensile stress shall be determined by Figure 2.

4.2 Measurement of edge stress of glass without coating

4.2.1 Measurement principle

Put the sample in a plane polarized light field. Rotate the polarizer and analyzer to keep

their polarization axes orthogonal to each other and 45° to the direction of the sample's

principal stress which is parallel or vertical to the edge of the sample. Put a 1/4 wave plate

in the left light path close to the analyzer. And make it parallel to its fast axis, slow axis and

polarization axis. Compensate by rotating the analyzer to obtain the compensation angle.

4.2.5 Test procedures

4.2.6 Test results calculation

Edge stress is calculated by Formula (4).

4.2.7 Test Report

The report shall include the following contents.

4.3 Test of edge stress of glass with coating

4.3.1 Principles of test

Use reflective light path to put the concentrator system, the polarizer and the analyzer

receiving reflective light on the same side of the sample, so as to ensure that the polarized

light can be reflected back by the coating on the back of the glass after entering into the

glass, and then going through the glass sample under test. The testing principle of this

test method is same as 4.2.1.And the only difference is that the polarized light passes

through the glass sample under test twice from the direction of the thickness of the glass.

4.3.2 Test device

Reflective edge stress gauge. It is mainly consisted of four parts, namely, concentrator

system, polarizer, analyzer, and 1/4 wave plate. The instrument structure is shown in

4.3.3 Sample

Use the finished product as sample. The edge on one side of it shall be coated (such as

curtain wall glass, glaze surface of car's shatter-proof glass). In order to avoid the

generation of thermal stress, the temperature inside and outside the sample must be

consistent and be same with the ambient temperature.

4.3.4 Determination of the edge stress measuring points

Same as 4.2.4.

4.3.5 Test procedures

Test procedures are as follows.

4.3.6 Test results calculation

Edge stress shall be calculated according to Formula (5) and (6).

4.3.7 Test Report

Same as 4.2.7.

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