Method of caustics for the study of cracked plates made of viscoelastic materials

Theocaris, PS

dc.contributor.author	Theocaris, PS	en
dc.date.accessioned	2014-03-01T01:05:31Z
dc.date.available	2014-03-01T01:05:31Z
dc.date.issued	1974	en
dc.identifier.issn	0020-7403	en
dc.identifier.uri	https://dspace.lib.ntua.gr/xmlui/handle/123456789/8862
dc.subject.classification	Engineering, Mechanical	en
dc.subject.classification	Mechanics	en
dc.title	Method of caustics for the study of cracked plates made of viscoelastic materials	en
heal.type	journalArticle	en
heal.identifier.primary	10.1016/0020-7403(74)90051-4	en
heal.identifier.secondary	http://dx.doi.org/10.1016/0020-7403(74)90051-4	en
heal.language	English	en
heal.publicationDate	1974	en
heal.abstract	The optical method of caustics was used for the evaluation of the stress intensity factor at the crack tip in a viscoelastic plate made of polycarbonate of bisphenol A and containing a single external crack under conditions of generalized plane stress. It was assumed that the crack developed in a linear viscoelastic material. The reflected rays from both lateral faces, as well as the transmitted rays of a normally incident light beam were significantly dispersed at the close neighborhood of the crack tip because of the excessive lateral constraint and the strong variation of the refractive index, and concentrated along singular curves (caustics) at some distances from the plate. The reflected caustics formed two branches. While the internal branch, which was formed by reflections from the front face, depended only on the elastic modulus (E) and Poisson's ratio (v) of the material, the external branch, formed by reflections from the rear face, depended on E and v, as well as on the refractive index of the material (n). The transmitted rays formed the same type of caustic as that which was formed by reflections from the rear face, but with a different size. By studying the relative position and shape of the two reflected branches and their variation with time, information was derived concerning the viscoelastic state of the material at fracture. The transmitted light caustic was used as a check on the results. A series of viscoelastic tests in pure tension at various stress and strain levels yielded the variation of the mechanical (E, v) and optical (n, cr, cf) properties of the material with applied stress and strain. The values of these quantities at each stress level allowed the plotting of the relative positions of the two branches of the reflected caustics. Comparison of the actual position of the caustics at the crack tip with the caustic nomogram yielded the viscoelastic behavior of the material during the progress of loading. It was shown that by increasing the loading mode a strong viscoelastic behaviour was apparent which influenced considerably the fracture mode of the plate. © 1974.	en
heal.publisher	PERGAMON-ELSEVIER SCIENCE LTD	en
heal.journalName	International Journal of Mechanical Sciences	en
dc.identifier.doi	10.1016/0020-7403(74)90051-4	en
dc.identifier.isi	ISI:A1974U786900001	en
dc.identifier.volume	16	en
dc.identifier.issue	12	en
dc.identifier.spage	855	en
dc.identifier.epage	860	en