| 摘要 |
1, 185, 472. Optical testing apparatus. TRIPLEX SAFETY GLASS CO. Ltd. Sept.11, 1967 [Sept.13, 1966], No.40754/66. Heading G2J. Apparatus for testing a piece of uniformly toughened glass in the form of a flat strip 26, comprises a device 10 for generating a beam 27 of circularly or elliptically polarized light, prisms 15, 16 for engaging a flat surface and an edge surface of the strip respectively and having inclined faces 18, 20 whereby the beam 27 enters the strip 26 from prism 15 at a small angle of less than 10 degrees to its surface and then passes via prism 16 to an analyzer 21 comprising a Babinet compensator 23 and a circularly polarizing eye-piece 24, the relative retardation of the polarization components of beam 27 being measured as an indication of the internal stresses of the glass. Prisms 15, 16 are of the same refractions index as the test glass and rest in a film of liquid also of the same refractive index. Beam 27 may consist of two mutually inclined plane polarized beams. White or monochromatic light is used, providing a single fringe or a series of equally spaced fringes whose inclination to the direction for unstressed glass is related to the tensile stress in the glass. A modification uses a mercury vapour source and projects fringes on to a screen. |
