When people observe toughened U-shaped glass at a certain distance and angle under certain lighting conditions, they will see some irregular colored stripes on the surface of toughened U-shaped glass, these colored streaks are known as“Stress spots,” and although the presence of stress spots does not affect the reflection of the U-shaped glass (there is no distortion) , also does not affect the transmission effect of u-glass (does not affect the resolution, and will not produce optical deformation) .

It is an optical property that all toughened u-glass has, and it is not the quality problem or quality defect of toughened u-glass, but toughened u-glass is used more and more widely as safety u-glass, the appearance of U-shaped glass is required more and more, especially when it is used as large-area curtain wall, the appearance of U-shaped glass will be adversely affected by the presence of stress spots on toughened U-shaped glass, even affect the overall aesthetic effect of the building, so people pay more and more attention to stress spots.

Causes of stress spots

All transparent materials can be divided into isotropic materials and anisotropic materials. When the light passes through the isotropic material, the speed of light is the same in all directions, the outgoing light and the incident light have no change, the well-annealed U-shaped glass belongs to the isotropic material.

Toughened U-shaped glass as a variety of hetero-materials, the phenomenon of stress spots can be explained by the photoelastic principle: When a polarized light passes through a toughened U-shaped glass, there is a stress (toughened stress) in the U-shaped glass, the light is split into two polarized beams, fast and slow, called birefringence, which travel at different speeds. When the two beams formed at one point intersect with the beam formed at another point, the interference will occur because of the phase difference between the two beams at the point of intersection due to the different propagation speed of the light, when the two light beams have the same amplitude direction, the light intensity will increase, resulting in bright field of view (bright spot) , and when the light amplitude direction is opposite, the light intensity will decrease, resulting in dark field of view (dark spot) . As long as there is non-uniform stress distribution in the plane direction of toughened u-glass, stress spots will occur.

In addition, the reflection effect on the surface of U-shaped glass makes the reflected light and the transmitted light polarize to a certain extent. The light entering the inner part of U-shaped glass is actually the light with a polarizing effect, that's why you see stripes or stripes that are light and dark.