GB/T 36405-2018Test method for stress in flat glass (English PDF)

3.1 Plane Stress

Plane stress is permanent tensile stress or compressive stress that exists among different areas of plane glass after the glass is molded.

3.2 Interior Stress

It is permanent stress generated by temperature gradient under the plate thickness direction after the glass is molded. Compressive stress exists on the surface, and tensile stress exists in the central area.

3.3 Polarizer

Polarizer is placed between light source and the sample being tested. It turns natural light into a device with plane polarized light and a certain vibration direction.

3.4 Analyzer

Analyzer is placed between the sample being tested and the observer. It is a polarizing device adopted to analyze polarization.

5.1.3.2 Sample processing

Rinse the sample, guarantee that the surface is clean and there's no attachment.

5.1.4 Determination of test area

The central section (diameter. 500 mm) of the sample is test area.

5.1.5 Test steps

Please see the test steps below.

a) Measure the thickness of the sample (accurate to 0.1 mm);

b) Activate stress detector; make the main direction of the polarizer and analyzer mutually orthogonal;

c) Place the test sample between the polarizer and analyzer, then, make the surface of the sample vertical to the optical path; horizontally place the samples in accordance with the pulling direction;

d) Operate the stress detector through the test and control software in accordance with the instrument specification, then, complete the stress test and calculation of the test area;

e) Record stress distribution diagram and the measured stress value of various points in the test area in accordance with the sample number.

5.1.6 Expression of test result

5.1.6.1 Plate stress distribution diagram

Calculate the stress value of the test area of the test sample in accordance with Formula (6). Calculate the absolute value of the stress value on the plane of x y coordinate; draw the plane stress distribution of the test sample with grayscale or colors.

5.1.6.2 Average value of plate stress

Calculate the positive value of tensile stress and compressive stress; calculate the arithmetic mean value of stress within the test area.

5.1.6.3 Maximum value of plate stress

The maximum value of the absolute value of stress within the test area.

5.2.4 Stress calculation

Birefringence optical path difference Delta (x, y) shall be calculated in accordance with Formula (2). Plate thickness stress of various test points shall be calculated in accordance with Formula (10).

Where:

sigma (x, y) - The stress value of the test sample, expressed in (MPa);

C - The stress-optical constant of the test glass, expressed in (MPa-1); the stress-optical constant of soda-lime silica glass shall be calculated as 2.6 x 10^-6 MPa-1;

d - The distance of light transmission in the glass, expressed in (mm); the actual measured value between the two polished sides in the central part of the test sample shall be calculated;

Delta (x, y) - The birefringence optical path difference of the test sample, expressed in (nm).

5.2.5 Plate thickness stress distribution curve

In terms of different y in Formula (10), respectively take 20 adjacent pixels in the central part of the sample under x direction. Calculate the distribution curve of stress arithmetic mean value that corresponds with the various y values; smooth and fit. Uniformly take 50 points of y in accordance with glass plate thickness. Obtain plate thickness stress distribution curve sigma (y), as it is shown in Figure 6. […]