City Research Online

Abstract

A photographic method is presented that provides full field fractional fringe orders without any auxiliary equipment on lens or diffused-light polariscopes. The boundary lines between dark and bright bands on a high contrast film and the equidensity lines obtained by pseudo-solarization or an Agfacontour film represent lines of constant fractional fringe order in an isochromatic pattern. The position of these lines in the field of the model and hence their fractional order can be changed by variation of exposure time and/or load when high contrast or Agfacontour film is exposed directly in the camera, or by changing the copying exposure time when an original negative on low-contrast film is copied through yellow light onto Agfacontour film. The boundary or equidensity lines can be calibrated in terms of fractional order or principal stress difference by means of a separate calibration model such as a beam in pure bending or in terms of fractional order only by means of a self-calibration procedure when a separate calibration model cannot be used. Fringe orders can be measured to an accuracy of 1% or better and the sensitivity/for evaluation is considerably increased (50 times or more).

The undesirable effects of a central intense spot normally obtained at the image plane of the camera on a lens polariscope can be reduced or eliminated by using a small camera aperture or a semi-diffused light polariscope. Special problems investigated include: study of optical creep and residual stresses, determination of stress concentration factor when the image on the film is very small, determination of full-field fractional fringe orders in slices of three-dimensional stress-frozen models. i Full-field fractional isochromatic fringes without isoclinics can be obtained by photographic double exposure on a plane polariscope so that quarter-wave plates are not needed for accurate evaluation.

A number of photographic methods are proposed to obtain pure and sharpened isoclinics in sensitive model materials. The equal intensity concept allows accurate point-by-point construction of isoclinics over the whole field when the isoclinic is known at one point and the isochromatic pattern is available. With a single orientation of the crossed polaroids, three isoclinic parameters can be obtained simultaneously over an extended region.

Publication Type:	Thesis (Doctoral)
Subjects:	Q Science > QC Physics T Technology > TA Engineering (General). Civil engineering (General) T Technology > TR Photography
Departments:	School of Science & Technology > Department of Engineering School of Science & Technology > School of Science & Technology Doctoral Theses Doctoral Theses

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