GB/T 15726-2021Glassware—Stress examination methods (English PDF)

3.1 Polarizer

An optical device, through which natural light is converted into plane polarized light with a certain vibration direction.

NOTE: Polarizer is usually placed between the light source and the specimen being tested, also known as a polarizer [Translator's note. Only different Chinese names are given here.].

3.2 Analyzer

An optical device, through which natural light is converted into plane polarized light with a certain vibration direction.

NOTE: Analyzer is usually placed between the observer and the specimen being tested, also known as an analyzer [Translator's note. Only different Chinese names are given here.].

7.1 Environmental requirements for polarizing stress meter

The polarizing stress meter shall be installed in an environment with a temperature of 10 °C ~ 35 °C, a relative humidity of less than 80 %, and dim light.

7.2 Zero-point adjustment of polarizing stress meter

When a quarter-wave plate is placed, the field of view shall be the darkest; when a full- wave plate is placed, the field of view shall be purple-red.

7.3 Qualitative measurement of birefringence optical path difference

Place a full-wave plate, place the specimen to be tested in the field of view, and observe the interference color. If it is still purple-red or only slightly changed, it means that the optical path difference of the specimen is very small; if the interference color of a certain part of the specimen is sky blue, green or orange-red, yellow, it means that the birefringence optical path difference of that part is large, and the internal stress trend of that part can be judged.

7.4.1 Measurement of bottom or similar bottom of colorless glass specimens

Place a quarter-wave plate in the field of view and adjust the zero point of the polarizing stress meter to make it a dark field of view. Place the specimen in the field of view and observe the bottom from the mouth. At this time, a dark cross will appear in the field of view. If the stress of the specimen is small, the dark cross will be blurred. Rotate the analyzer to separate the dark cross into two arcs moving in opposite directions. As the dark area moves outward, blue-gray appears on the concave side of the arc and brown appears on the convex side. If the stress value of a selected point is measured, rotate the analyzer until the blue-gray color at that point is just replaced by brown. Rotate the specimen around the axis to find the maximum stress point, rotate the analyzer until the blue-gray color is replaced by brown, record the rotation angle of the analyzer at this time, and measure the specimen thickness at that point.

7.4.2 Measurement of side wall of colorless glass specimens

Place a quarter-wave plate in the field of view and adjust the zero point of the polarizing stress meter to make it a dark field of view. Place the specimen in the field of view so that the axis of the specimen is 45° to the polarization plane. At this time, different bright and dark areas appear on the side wall. Rotate the analyzer until the dark areas on the side wall gather and just completely replace the bright areas. Rotate the specimen around the axis to determine the maximum stress area. Record the analyzer placement angle where the maximum stress area is measured, and measure the thickness of the two side walls of this area (the sum of the thickness of the two side walls). If the light and dark changes unsteadily at the dark gathering area, find a reference area nearby.

The optical path difference of this reference area shall be small or constant, or both. At this time, first measure the optical path difference of the reference area, and then slightly tilt it so that the light passes through a layer of reference area and a layer of wall thickness of the area to be measured. The optical path difference value minus half of the optical path difference of the reference area is the optical path difference of the