Quantitative determination of vacuum degree of glass with photoelasticity

Vacuum glass is an environmentally friendly and energy-saving building glass. The degree of vacuum, which is a key factor associated to its characteristics, is of great interest to monitor during the service time. In this study, a real-time inspection method based on photoelasticity has been proposed to determine the vacuum degree of glass. The isochromatic phase map is achieved by means of real-time phase shifting while the polarized light passes through the glass and is recorded with a polarization camera. After the stress state of the glass near the support is analyzed with numerical modeling based on the stress-optic law and Mueller matrix multiplication, the relationship between the vacuum degree of glass and the equivalent radius near the support is established. An experimental illustration is presented on a piece of vacuum glass, which shows that the equivalent radius is effective parameter in identifying the degree of vacuum for the glass structures.