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Experimental Mechanics

, Volume 11, Issue 11, pp 481–489 | Cite as

A method for directly determining surface strain fields using diffraction gratings

Method proposed by author is based on a spatial filtering process carried out on the diffraction pattern generated by a grating applied to the specimen surface
  • Pierre M. Boone
Article

Abstract

This paper describes a new method for determining the strain distribution at the surface of solid bodies. The method is purely optical; it uses the diffraction phenomena generated by a copy of a grating that is applied to the specimen. A suitable mask performs filtering of the diffraction pattern; the image that is reconstructed from this filtered pattern shows light and dark areas; it is shown that the boundary line of those areas is the locus of points exhibiting the same value of strain, measured along a certain direction.

The magnitude of the strain can be easily calculated; it can be adjusted by a simple translation of the filter. A theoretical description of the system and some experimental results are presented.

Keywords

Mechanical Engineer Diffraction Pattern Fluid Dynamics Strain Field Strain Distribution 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

List of Symbols

A.E. (m)

absolute error onm

do

distance between object plane and lens

f

focal distance

F{f(x, y)}

Fourier transform off(x, y)

j

imaginary unit

p

shift of a diffraction point in the direction perpendicular to the grating lines

q

shift of a diffraction part in the direction parallel to the grating lines

R.E. (m)

relative error onm

T(x, y)

amplitude distribution of a transparency

To (T1)

period of an undeformed (deformed) line grating, measured perpendicular to the grating lines

To

period of a deformed line grating measured along the originalx-axis

u, v

coordinates in the Fourier plane

uo (u1)

distance between the optical axis and the first-order diffraction point of a grating of periodT o (T1)

uM

distance between the edge of the spatial filter and the optical axis, measured perpendicular to original grating lines

V(u, v)

amplitude distribution in the Fourier plane before filtering

x, y

coordinates in object and image plane

α

rotation angle

γxy

shear strain inxy-plane

ε

normal strain

λ

wavelength of light

ω

rigid-body rotation

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Copyright information

© Society for Experimental Mechanics, Inc. 1971

Authors and Affiliations

  • Pierre M. Boone
    • 1
  1. 1.Laboratory for Strength of Materials, Stress Analysis DivisionUniversity of GhentGhentBelgium

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