Polariscope and Photoelasticity
A Photolastic, Inc. polariscope is utilized for photoelastic demonstrations and studies. Specimen fixtures are attached to a load cell and specimen loading is applied via a manual leadscrew. A load cell readout displays the applied load.
A monochromatic light source is used to better define the fringes. Light passes through two plates made of polarizing material--these are the polarizer and the analyzer. The specimen is fixtured and loaded between these plates. The analyzer is rotated either to be parallel or perpendicular to the polarizer for a bright field or dark field, respectively.
Loaded specimens are viewed through the analyzer. Images can be displayed on a computer monitor via a computer-interfaced digital camera. RinconHD image capturing and measurement software and a 3MP USB camera are employed.
The lock on the orientation hand wheel is placed in the D (direction) position to observe isoclinic fringes for principle direction data. When the lock is moved to the M (magnitude) position, quarter wave plates on the specimen side of each polarizing plate are rotated to be 45° to the polarizing axes. Only isochromatic fringes are observed. Each fringe represents a constant difference in the magnitude of principle stresses.
With data from both types of fringes, a complete state of stress may be determined.