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A new holographic interferometer for stress analysis

In the system developed by the authors, isopachics and isochromatics can be viewed separately and simultaneously

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Abstract

In holographic interferometry with a photoelastic model, two families of fringes are generated simultaneously when the model is stressed. One family represents the isochromatic-fringe pattern normally associated with photoelasticity which yields the difference between the principal stresses. The other family represents the isopachic-fringe pattern associated with interferometry which yields the sum of the principal stresses. From these complementary patterns, the magnitudes of the principal stresses can readily be determined throughout the field of observation. Unfortunately, these fringe patterns are not completely independent but interact in such a way as to make interpretation difficult in critical regions of the model. A new system has been developed which readily permits simultaneous acquisition of these fringe patterns without their undesirable mutual interaction, as well as providing increased sensitivity.

This new interferometer uses a double-pass object beam and an optical rotator to eliminate the isochromatic-fringe pattern and its effect from the isopachic interferogram. Such a system has considerable value in experimental mechanics for applications to both static and dynamic model studies and to materials investigation.

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Abbreviations

A :

position of collimating lens

A 1,A 2 :

components of the complex amplitudes of the light in the directions of σ1 and σ2

A R :

complex amplitude of the reconstructed light wave

\(A_{T_1 } , A_{T_2 }\) :

total-complex-amplitude components

B, ΔB :

focal point of lenses and lateral displacement of the focal point, respectively

C 1,C 2 :

stress-optic coefficients

FL :

focal length

H :

magnetic-field intensity

I :

light intensity

M :

maximum image-specimen misalignment

N,N ∞ :

local and remote fringe counts, respectively

V :

Verdet constant

a :

radius of hole in specimen

a 0 :

magnitude of the light vector

k :

wave number 2π/λ

t, t 0 :

thickness of loaded and unloaded specimen, respectively

n 0 :

index of refraction of unstressed material

n 1,n 2 :

indices of refraction of stressed material associated with directions of σ1 and σ2

r, θ:

polar coordinates

x, y :

rectangular coordinates

λ:

wavelength of light

ϕ:

phase of wavefront

δφ1, δφ2 :

change of phase associated with σ1 and σ2

σ:

remote tensile stress

σ1, σ2 :

principal stresses

θS :

rotation angle of polarization ellipse

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Authors and Affiliations

  1. Bell Laboratories, 07981, Whippany, N. J.

    R. O'Regan (member of Technical Staff) & T. D. Dudderar (member of Technical Staff)

  2. 07901, Murray Hill, N. J.

    R. O'Regan (member of Technical Staff) & T. D. Dudderar (member of Technical Staff)

Authors
  1. R. O'Regan
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  2. T. D. Dudderar
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O'Regan, R., Dudderar, T.D. A new holographic interferometer for stress analysis. Experimental Mechanics 11, 241–247 (1971). https://doi.org/10.1007/BF02329034

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  • DOI: https://doi.org/10.1007/BF02329034

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