Measurement of Glass Stress—Optical Coefficient ASTM C770
ASTM C770 test method includes procedures for measuring the stress-optical coefficient of glass used in photoelastic analysis. The standard units of the stress-optical coefficient are mm²/N.
Scope:
ASTM C770 is useful in determining the magnitude of residual thermal stresses for pre-stressing (tempering) or annealing glass. This standard test method is also helpful for deciding optical retardation for a beam of a glass of rectangular cross-section when subjected to uniaxial tension, four-point bending, and uniaxial compression. Stress-optical coefficients mainly determine stress in the glass.
Test Procedure:
| Test Method | Section |
| Procedure A (Uniaxial tension) | 4.1.1 |
| Procedure B (Beam Bending) | 4.1.2 |
| Procedure C (uniaxial compression) | 4.1.3 |
Specimen Size :
The stress optical coefficients K are calculated at a wavelength of λ = 0.5893 µm and temperature of 21°C. The measurement accuracy is ± 3% or ± 0.06·10–6 mm²N–1.
Data:
n = refractive index.
E = Young’s modulus.
µ = Poisson number.
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