PDF GB/T 15726-2021 English (GB/T 15726-1995: Older version)
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Glassware - Stress examination methods
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GB/T 15726-2021: PDF in English (GBT 15726-2021) GB/T 15726-2021
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 81.040.01
CCS N 64
GB/T 15726-2021
Replacing GB/T 15726-1995
Glassware - Stress examination methods
ISSUED ON. AUGUST 20, 2021
IMPLEMENTED ON. MARCH 01, 2022
Issued by. State Administration for Market Regulation;
Standardization Administration of the People’s Republic of China.
Table of Contents
Foreword... 3
1 Scope... 4
2 Normative references... 4
3 Terms and definitions... 4
4 Principle... 4
5 Specimens... 5
6 Instruments... 5
7 Test steps... 5
8 Result calculation... 7
9 Examination report... 8
Glassware - Stress examination methods
1 Scope
This document specifies the terms and definitions, principle, specimens, instruments,
test steps, result calculation, and examination report for the internal stress examination
of glassware.
This document apples to the internal stress examination of glassware after annealing.
2 Normative references
This document has no normative references.
3 Terms and definitions
For the purpose of this document, the following terms and definitions apply.
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.].
4 Principle
4.1 Glass is usually an isotropic homogeneous material. When internal stress exists, it
exhibits anisotropy and produces birefringence of light. This method uses a polarizing
stress meter to measure the birefringence optical path difference, and the value of the
birefringence optical path difference per unit thickness is used to represent the
magnitude of the product’s internal stress.
4.2 The stress optical constants of the same type of glass are the same, and the value of
the birefringence optical path difference per unit thickness is used to represent the
magnitude of its internal stress.
4.3 This method uses a polarizing stress meter to measure the birefringence optical path
difference, and calculates the magnitude of internal stress through the birefringence
optical path difference.
5 Specimens
5.1 The specimens shall be glassware that have not been subjected to other tests after
annealing.
5.2 The specimens shall be placed in the laboratory for more than 30 min in advance.
5.3 Wear gloves during examination to avoid direct contact with the specimens with
your hands.
6 Instruments
6.1 When using polarizing elements and protective parts for observation, the brightness
of the edge of the light field shall not be less than 120 cd/m2.
6.2 The polarizing element used shall ensure that the polarization degree at any point
in the bright field is not less than 99 %.
6.3 The polarization field shall not be less than 85 mm.
6.4 A 565 nm full-wave plate (sensitive color plate) and a quarter-wave plate can be
placed between the polarizer and the analyzer. The slow axis of the wave plate is 90° to
the polarization plane of the polarizer.
6.5 The analyzer rotates relative to the polarizer and the full-wave plate or quarter-wave
plate, and there is a device for measuring the rotation angle (the scale value is 1°).
6.6 The accuracy of the polarizing stress meter is ≥ 3 nm.
7 Test steps
7.1 Environmental requirements for polarizing stress meter
The polarizing stress meter shall be installed in an environment with a temperature of
10 ℃ ~ 35 ℃, 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 Quantitative test method for internal stress of colorless glass specimens
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
......
Source: Above contents are excerpted from the PDF -- translated/reviewed by: www.chinesestandard.net / Wayne Zheng et al.
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