page_title: Photoelasticity
section_title: Two-dimensional photoelasticity
hierarchical_section_title: Photoelasticity / Two-dimensional photoelasticity
caption_attribution_description: Picture of a CD plastic cover between a polarizer and a flat screen monitor. The flat screen light is polarized, so the birefringence of the plastic layer shows colored fringes after the polarizer. Also called Photoelasticimetry or en:Photoelasticity. Made by me.
context_page_description: Photoelasticity describes changes in the optical properties of a material under mechanical deformation. It is a property of all dielectric media and is often used to experimentally determine the stress distribution in a material, where it gives a picture of stress distributions around discontinuities in materials. Photoelastic experiments are an important tool for determining critical stress points in a material, and are used for determining stress concentration in irregular geometries.
context_section_description: Photoelasticity can describe both three-dimensional and two-dimensional states of stress. However, examining photoelasticity in three-dimensional systems is more involved than two-dimensional or plane-stress system. So the present section deals with photoelasticity in a plane stress system. This condition is achieved when the thickness of the prototype is much smaller as compared to dimensions in the plane. 
  Thus one is only concerned with stresses acting parallel to the plane of the model, as other stress components are zero. The experimental setup varies from experiment to experiment. The two basic kinds of setup used are plane polariscope and circular polariscope.
  The working principle of a two-dimensional experiment allows the measurement of retardation, which can be converted to the difference between the first and second principal stress and their orientation. To further get values of each stress component, a technique called stress-separation is required. Several theoretical and experimental methods are utilized to provide additional information to solve individual stress components.
caption: Photoelastic experiment showing the internal stress distribution inside the cover of a Jewel case
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