Apparatus for determination of elastic isodynes and of the general state of birefringence whole field-wise using the device for birefringence measurements in a scanning mode (isodyne polariscope)

摘要

An apparatus has been developed to experimentally determine the state and amount of birefringence in an arbitrary plane within a birefringent body using an entirely new method. Such information can be used to determine the optical anisotropy in solid and liquid bodies, residual and induced stress fields, etc. This apparatus uses a collimated and polarized light beam which scans linearly the plane of measurement within a transparent birefringent or photoelastic object, and a device which collects particular sheets of light scattered along the path of the light beam, the intensity of which is directly related to the state of birefringence at each scattering point at the plane of measurement within the birefringent body. An imaging device produces in the image plane of the apparatus the lines of constant light intensities which are the lines of constant values of accumulated birefringence. For plane stress states in engineering objects such lines are identical with the elastic isodynes and are therefore called photoelastic isodynes. Two independent fields of such isodynes allow the direct determination of all three stress components of the plane stress state and give an additional relation between the strees components. This is the only experimental method which supplies directly four or more independent data on the stress state at each point within the photoelastic object.