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GB/T 15726-1995 PDF in English

GB/T 15726-1995 (GB/T15726-1995, GBT 15726-1995, GBT15726-1995)
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GB/T 15726-1995: PDF in English (GBT 15726-1995)

GB/T 15726-1995
ICS 71.040.20
N 64
Glassware - Stress examination methods
Issued by. State Bureau of Technical Supervision
Table of Contents
1 Subject content and scope of application ... 3 
2 Principle ... 3 
3 Specimen ... 3 
4 Instruments ... 4 
5 Testing procedures ... 4 
6 Representation of test results ... 6 
7 Testing report ... 7 
Additional information ... 7 
Glassware - Stress examination methods
1 Subject content and scope of application
This standard specifies the principle, specimen, instrument, procedure,
calculation method and report content of the stress examination of glassware.
This standard applies to the stress examination of glassware after annealing.
2 Principle
Usually glass is an isotropic homogeneous material. When stress exists, it will
exhibit anisotropy and produce birefringence of light. The optical path difference
of birefringence ΔS has a relationship with stress.
ΔS - The optical path difference of birefringence;
σ - The difference of the two principal stresses perpendicular to the direction
of light propagation, N/mm2;
K - The stress optical constant of glass, 10-6 mm2/N;
d - The length (thickness) of optical path in the glass specimen, cm.
The stress optical constant K of the same type of glass is the same, so it may
use the difference of optical path per unit thickness to express the magnitude
of the stress. This standard specifies the measurement method of using the
polarized stress meter to measure the difference of optical path, as well as
using the difference of optical path per unit thickness to indicate the internal
stress of the product.
3 Specimen
3.1 The specimen shall be a glass instrument that has not been tested after
3.2 Specimen must be placed in the laboratory in advance for more than 30
minutes. Place the sample to be tested into the dark field of view wherein a
quarter-wave plate is placed, 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,
then the dark cross is blurred. Rotate the analyzer to separate the dark cross into two arcs moving in
opposite directions. As the dark area moves outward, the concave side of the
arc will appear blue-gray. Continue to rotate the analyzer until the blue-gray is
just replaced by brown. Rotate the specimen around the axis to find the maximum stress point,
rotate the analyzer until the blue-gray is replaced by brown, record the angle of
rotation of the analyzer as well as the thickness of the point.
5.4.2 Measurement of sample walls or similar walls Place the sample into the field of view, so that the axis of the sample is
at 45° with the plane of polarization. At this time, there will be different areas of
light and dark on the sample wall, select the brightest point, which is the
maximum stress point. Rotate the analyzer, until the dark area on the wall is converging to
completely replace the bright area. Read the angle of rotation of the analyzer
and rotate the sample slightly along the axis. If the converged dark area is
stable in brightness, the wall thickness of the two layers of glass is the length
of its optical path. If the brightness of the converged dark area changes indefinitely, find a
reference area nearby, which shall have a small or constant optical path
difference or both, then follow clause to determine the optical path
difference of the reference area, then slightly tilt it to make the light pass through
the wall thickness of one layer of reference area and one layer of tested area;
use the obtained optical path difference to minus 1/2 of the optical path
difference of the reference area, to obtain the optical path difference of the
single-layer wall of the measured part. If the oblique angle from the vertical is
greater than 10°, it shall follow the diagram below to calculate the actual optical
Source: Above contents are excerpted from the PDF -- translated/reviewed by: www.chinesestandard.net / Wayne Zheng et al.