Editing Photoelasticity (section)

== History ==
{{See also|Physical crystallography before X-rays#Photoelasticity}}
The photoelastic phenomenon was first discovered by the Scottish [[physicist]] [[David Brewster]], who immediately recognized it as stress-induced [[birefringence]].<ref>{{cite journal | doi=10.1098/rstl.1815.0004 | title=Experiments on the depolarisation of light as exhibited by various mineral, animal, and vegetable bodies, with a reference of the phenomena to the general principles of polarisation |last=Brewster |first=David | journal=Philosophical Transactions of the Royal Society of London | year=1815 | volume=105 | pages=29–53 | doi-access=free }}</ref><ref>{{cite journal | doi=10.1098/rstl.1816.0011 | title=On the communication of the structure of doubly refracting crystals to glass, muriate of soda, fluor spar, and other substances, by mechanical compression and dilatation |last=Brewster |first=David | journal=Philosophical Transactions of the Royal Society of London | year=1816 | volume=106 | pages=156–78 | s2cid=108782967 }}</ref> That diagnosis was confirmed in a direct refraction experiment by [[Augustin-Jean Fresnel]].<ref name=fresnel-1822s>{{cite journal |last=Fresnel |first=Augustin |year=1822 |title=Note sur la double réfraction du verre comprimé |journal=Annales de Chimie et de Physique |series=Série 2 |volume=20 |pages=376–83 }}
* Reprinted in H.&nbsp;de Senarmont, E.&nbsp;Verdet, and L.&nbsp;Fresnel (eds.), ''Oeuvres complètes d'Augustin Fresnel'', vol.&nbsp;1 (1866), [https://books.google.com/books?id=1l0_AAAAcAAJ&pg=PA713 pp.&nbsp;713–18]
* Translated as {{cite journal | doi=10.5281/zenodo.4706835 | year=2021 | last1=Fresnel | first1=Augustin-Jean | translator-last=Putland | translator-first=Gavin Richard | title=Note on the double refraction of compressed glass }}</ref> Experimental frameworks were developed at the beginning of the twentieth century with the works of [[Ernest George Coker|E.G. Coker]] and [[Louis Napoleon George Filon|L.N.G. Filon]] of [[University of London]]. Their book ''Treatise on Photoelasticity'', published in 1930 by [[Cambridge Press]], became a standard text on the subject. Between 1930 and 1940, many other books appeared on the subject, including books in Russian, German and French. [[Max M. Frocht]] published the classic two volume work, ''Photoelasticity'', in the field.<ref>{{cite book |date=1969 |title=Photoelasticity|pages=xi–xii|editor-last=Leven|editor-first=M.M.|publisher=Pergamon|doi=10.1016/B978-0-08-012998-3.50005-7 |language=en|isbn=978-0-08-012998-3|editor2-last=Frocht|editor2-first=M.M.|chapter=Vita Max Mark Frocht }}</ref> At the same time, much development occurred in the field – great improvements were achieved in technique, and the equipment was simplified. With refinements in the technology, photoelastic experiments were extended to determining three-dimensional states of stress. In parallel to developments in experimental technique, the first phenomenological description of photoelasticity was given in 1890 by [[Friedrich Carl Alwin Pockels|Friedrich Pockels]],<ref>{{cite journal | doi=10.1002/andp.18902750313 | title=Ueber die durch einseitigen Druck hervorgerufene Doppelbrechung regulärer Krystalle, speciell von Steinsalz und Sylvin | year=1890 | last1=Pockels | first1=F. | journal=Annalen der Physik und Chemie | volume=275 | issue=3 | pages=440–69 | bibcode=1890AnP...275..440P | url=https://zenodo.org/record/2108114 }}</ref> however this was proved inadequate almost a century later by Nelson & [[Melvin Lax|Lax]]<ref>{{cite journal | doi=10.1103/PhysRevLett.24.379 | title=New Symmetry for Acousto-Optic Scattering | year=1970 | last1=Nelson | first1=D. F. | last2=Lax | first2=M. | journal=Physical Review Letters | volume=24 | issue=8 | pages=379–80 | bibcode=1970PhRvL..24..379N }}</ref> as the description by Pockels only considered the effect of mechanical strain on the optical properties of the material.

With the advent of the digital [[polariscope]] – made possible by light-emitting diodes – continuous monitoring of structures under load became possible. This led to the development of dynamic photoelasticity, which has contributed greatly to the study of complex phenomena such as [[fracture]] of materials.