Experimental Mechanics

, Volume 11, Issue 2, pp 49–56 | Cite as

Measurement of the strain field near a crack tip in polymethylmethacrylate by holographic interferometry

Real-time holographic interferometry is used to determine the averaged transverse-strain field in the vicinity of a sharp crack using strip specimens of transparent plastic loaded in tension
  • T. D. Dudderar
  • R. O'Regan


An experimental method has been developed for the detailed, real-time study of the strain field near a crack tip in any transparent material. This method combines holography and interferometry to measure the field of averaged transverse strain in a sheet specimen under inplane loading.

It is shown that the solution for an edge crack in a semi-infinite sheet based on two-dimensional linear elastic theory can be applied to the finite-width polymethylmethacrylate specimen. This solution is observed to become less valid as the crack tip is approached due to the breakdown of the plane-stress assumption. This effect is evaluated for a range of thicknesses from much less to much more than the crack length.


Mechanical Engineer Fluid Dynamics Experimental Method Polymethylmethacrylate Crack Length 
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List of Symbols


half-crack length (in.)


half width of specimen (in.)


length of scattering zone along the crack line (in.)


fringe order


fringe order remote from crack tip


fringe order at the crack line for the maximum scattering-zone radius


fractional deviation between the analytical and the actual fringe counts


distance from crack tip (in.)


distance from crack tip at which order deviates from that predicted by plane-stress theory (in.)


thickness of specimen (in.)


complex stress function for solution to the problem of an infinite plate with an array of uniformly spaced cracks loaded in biaxial tension


average transverse strain


transverse strain remote from crack tip


complex spatial argument,x+iy


correction function for effect of free edge


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Copyright information

© Society for Experimental Mechanics, Inc. 1971

Authors and Affiliations

  • T. D. Dudderar
    • 1
    • 2
  • R. O'Regan
    • 1
    • 2
  1. 1.Bell Telephone Laboratories, Inc.Murray Hill
  2. 2.Whippany

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