Photoelastic constant measurement method

  1. Measurement Principle
    The photoelastic constant of a sample can be measured by attaching a loading device to the ABR. By precisely measuring the birefringence induced by the load, the photoelastic constants can be accurately measured “automatically”. When an external load is applied to an elastic material, anisotropy is induced inside the sample in proportion to the magnitude of the load, resulting in birefringence. This proportionality constant is called the photoelastic constant. The photoelastic constant has a value specific to the material. In the case of crystals, the photoelastic constants are different depending on the direction of the crystal axis. The figure below shows an example of measurement by the “disk compression method,” but any loading method can be used upon request. By applying the calibration function of the ABR, the initial birefringence in the sample (residual stress during manufacturing, etc.) can be canceled, and the birefringence caused by the load can be measured separately. Therefore, the ABR is very effective especially for the measurement of samples with small photoelastic constants.