With traditional photoelasticity, an engineer had to deal with the tedium of both coating applications and fringe counting. With the GFP 1000, Photoelastic Strain Analysis (PSA) is now fully automatic. After you paint, just aim the polariscope at your component or specimen and "shoot." The image of the high strain or stress area is displayed digitally on the system's computer. The GFP 1000 system interpolates the data and outputs an image showing the maximum inplane shear and the direction of the first principal strain.
The Grey-field Polariscope illuminates the object with circularly polarized light. In the presence of shear strain, the light becomes elliptically polarized, where the degree of ellipticity in the light is proportional to the level of maximum shear strain.
Paint-on Photoelastic Coatings
Stress Photonics introduces an exiting new development; specially tinted paint-on coatings.
Paint-on coatings have been possible for many years, but were rarely used because the thickness of the coating directly effects the strain measurement and could not be accurately measured. Stress Photonics has developed a method for measuring the thickness of a paint-on coating automatically. The same automatic polariscope that measures the strain amplitude can measure the thickness of the coating, eliminating it as an unknown. The Grey-field Polariscope also works with all currently available photostress coatings (e.g. paste-on sheet, liquid contoured, etc.).
Automatic Coating Thickness Measurement
To automatically measure the coating thickness a tint is added which attenuates red (R), green (G), and blue (B) light to different degrees. Three colors and three separate attenuation functions are necessary in order to measure the birefringence and account for reflections and light intensity variations. A paint-on coating was applied to a wrench and the shear strains were measured by the polariscope as the wrench was being used to tighten a bolt.
For detailed information on paint on coatings see the "Specimen Preparation" section of the Online GFP 1000 Tutorial.