Abstract
A reflex camera that incorporates a light source and spectroscope for recording in-plane displacement fringes formed by reflective diffraction gratings is described and illustrated.
A technique for replicating reflective diffraction gratings on plane metallic surfaces is given in detail.
Typical fringe patterns of a mild-steel tension specimen containing a long shallow notch obtained using 6000-lines/inch gratings show the elastic deformation of the specimen.
The method should prove a useful supplement or alternative to reflective photoelasticity in elasto-plastic studies, particularly when strain distributions in the transition region are of interest.
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Abbreviations
- α:
-
angle of incidence
- β p :
-
angle of emergence ofp-th order passing through grating G1 at point A
- β p,s− :
-
angle of reflection ofp, s-p order sequence at point B
- β T :
-
angle of emergence ofp, s-p, r-s order sequence from grating G1 at point C
- φC :
-
phase of emergent beam on leaving point C
- ρC :
-
fractional displacement of the rulings of the reference grating G1 at point C with respect to those on the model grating G2 at point N
- λ:
-
wavelength of light
- a u :
-
amplitude ofu component of emergent sequence
- A :
-
amplitude of emergent sequence
- C c :
-
phase constant depending upon position of point C
- f A :
-
fractional position of point A in ruling
- k u :
-
phase constant depending upon order sequenceu
- r,s,p :
-
spectral order numbers
- t :
-
thickness of air gap
- u :
-
number defining order sequence
- x C :
-
ordinate of point C
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Middleton, E., Stephenson, L.P. A reflex spectrographic technique for in-plane strain analysis. Experimental Mechanics 8, 19–24 (1968). https://doi.org/10.1007/BF02326246
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DOI: https://doi.org/10.1007/BF02326246