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Stress-Optic Coefficient

https://en.wikipedia.org/w/index.php?title=Photoelasticity&oldid=1109858854#Experimental_principles

When a ray of light passes through a photoelastic material, its electromagnetic wave components are resolved along the two principal stress directions and each component experiences a different refractive index due to the birefringence. The difference in the refractive indices leads to a relative phase retardation between the two components. Assuming a thin specimen made of isotropic materials, where two-dimensional photoelasticity is applicable, the magnitude of the relative retardation is given by the stress-optic law \(\Delta ={\frac {2\pi t}{\lambda }}C(\sigma _{1}-\sigma _{2})\), where \(\Delta\) is the induced retardation, \(C\) is the stress-optic coefficient, \(t\) is the specimen thickness, \(\lambda\) is the vacuum wavelength, and \(\sigma_1\) and \(\sigma_2\) are the first and second principal stresses, respectively.

When a ray of light passes through a photoelastic material, its electromagnetic wave components are resolved along the two principal stress directions and each component experiences a different refractive index due to the birefringence. The difference in the refractive indices leads to a relative phase retardation between the two components. Assuming a thin specimen made of isotropic materials, where two-dimensional photoelasticity is applicable, the magnitude of the relative retardation is given by the stress-optic law Δ=((2πt)/λ)C(σ₁-σ₂), where Δ is the induced retardation, C is the stress-optic coefficient, t is the specimen thickness, λ is the vacuum wavelength, and σ₁ and σ₂ are the first and second principal stresses, respectively.