Editing Photoelasticity (section)

==Two-dimensional photoelasticity==
[[File:Photoelasticimetry1.JPG|thumb|Photoelastic experiment showing the internal stress distribution inside the cover of a [[Jewel case]]]]

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 than the dimensions in the plane.{{cn|date=September 2022}} 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.{{cn|date=September 2022}}

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.<ref>{{cite journal | doi=10.1243/03093247JSA583 | title=Stress-separation techniques in photoelasticity: A review | year=2010 | last1=Solaguren-Beascoa Fernández | first1=M. | last2=Alegre Calderón | first2=J.M. | last3=Bravo Díez | first3=P.M. | last4=Cuesta Segura | first4=I.I. | journal=The Journal of Strain Analysis for Engineering Design | volume=45 | pages=1–17 | s2cid=208518298 }}</ref> Several theoretical and experimental methods are utilized to provide additional information to solve individual stress components.