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Photoelastic strain gauge

  • US 4,123,158 A
  • Filed: 05/09/1975
  • Issued: 10/31/1978
  • Est. Priority Date: 05/09/1975
  • Status: Expired due to Term
First Claim
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1. A photoelastic strain gauge adapted to be bonded to a surface of a workpiece for displaying visual patterns representative of the strain in such workpiece, said strain gauge having a mounting plane adapted to be parallel to the workpiece surface, said strain gauge comprising two substantially parallel outer sheets of reflective material, a slab of photoelastic material between said outer sheets, an inner sheet of reflective material in said slab and being parallel to said outer sheets, said slab having an entry aperture for light to enter said slab and an exit aperture arranged to receive light which has passed through said slab to produce the visual patterns, first reflective means adjacent to one end of said slab for receiving light which has passed through said entry aperture and for directing such light at a predetermined angle so as to be reverberated within said slab between one of said outer sheets and said inner sheet, a further sheet of reflective material adjacent to the other end of said slab and being disposed substantially perpendicular to said inner and outer sheets and arranged to receive light which has been reverberated between said one outer sheet and said inner sheet and to reflect such light toward said second outer sheet for further reverberation between said second outer sheet and said inner sheets, and second reflective means adjacent to said one end of said slab for receiving light which has been reverberated by said sheets of reflective material and for directing such light to said exit aperture, thereby to increase the length of path of light through said slab so as to cause the visual patterns to be amplified, and to decrease the effects of bending and shear stresses in the workpiece.

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