ASTM-C770:16(R2020) pdf free download – Standard Test Method for Measurement of Glass Stress- Optical Coefficient.
4. 1.1.2 In Fig. 3(h) the fiber is stressed while immersed in a liquid which matches the refractive index of the fiber. This arrangement provides more satisfactory viewing of the fiber.
4.1.2 Procedure B:
4.1.2.1 The polarimetry apparatus for the beam-bending procedure is shown in Figs. 4 and 5. Radiation from a white-light source passes through the following components and in this sequence: a diffuser, a polarizer whose axis is at 45° to the vertical, the glass specimen, a quarter-wave plate, and a second polarizer (analyzer) whose axis is at 900 to that of the first polarizer.
4.1.2.2 A schematic of the loading scheme is shown in Fig.
5. Metal fixtures shall he provided to subject the specimen to four-point bending. A support span of 115 mm and a moment arm, a, of 45 mm are recommended. Dimensions within 5 % of these values are acceptable. Symmetrical loading is essential, and requires careful centering of the upper loading block. The knife edges shall be finished to approximately 5 mm radius. Loading can be accomplished through a yoke. which rests in a Vgroove in the upper loading block, and a weight pan as shown However, any convenient loading scheme at the center of the upper block may be used.
4.1.2.3 A polarimeter. with a rotating analyzer, calibrated to Practices C1426, and described in Test Method C1426 and in Section 6 of this test method, is used to observe the zero order (black) fringe in the mid-plane of the beam as a known load is applied. The readings from the analyzer scale arc used in the calculation of the stress-optical cocflicicnt.
4.1.3 Procedure C.
4.1.3.1 Polarimeter as described in Test Method F218.
4.1.3.2 Force application frame, an example of which is shown in Fig. 6(a) and Fig. 6(b). must include:
(a) A strain-gauge load cell and load cell indicator, capable of measuring the force applied within I % accuracy.
(1) Hydraulic or mechanical means of applying constant force and maintaining the force during the measuring time.
(c) Swivel-mounted loading blocks, otiering at least two degrees of swivel freedom, to avoid the loading on the edge.
4.2 Micrometer C’aliper for measuring specimen dimensi on s to 0.0025 mm (0. 000 1 in.).
4.3 Weights that are known to an accuracy of ± 1 %.
5. Test Specimen
5.1 Procedure A:
5.1.1 Select a mass of the glass to be tested that has good optical quality with no heavy cords or striae. By conventional lamp-working methods, draw 0.6 to 0.9 m (2 to 3 fi) of fiber from the glass. sufficient to provide fIve specimens 76 to 102 mm (3 (04 in.) long with taper (variation in diameter along the length) less than 0.025 mm (0.001 in.) and diameters in the range 0.635 mm (0.025 in.) to 0.760 mm (0.030 in.).