|
Stress Birefringence
When a material is placed under stress the distribution of the electrons in the
material is changed. The amount of change is different for each
material and is a characteristic of the material. The photoelastic constant of
the matrial is a measure of the electron displacement (strain) as a
function of the load (stress) applied as long as the deformation is elastic,
springs back when the load is removed. If the YOung's Modulus of the
matrial is exceeded then some of the deformation becomes permenant. In some
materials the applied load can be "frozen" in place, as in the case of
high stress glass sheet. Polarized light can make the displacement visible. Both
plastic deformation and elastic deformation result in an
anisotropic distribution of electrons in the material that becomes visible as
interference colors when the object is viewed between crossed linear or
crossed circular polarizing filters. Click on the photographs below for more
information.
Birefringence from Plastic Deformation in Human Skin Cells
Birefringence from Plastic Deformation in Dog Skin Cells
Stress Birefringence in Safety Glass
|
