HOLOGRAPHIC NONDESTRUCTIVE TESTING OF LAMINATES

Holography, a form of laser beam photography, is a relatively new technique that is being increasingly used for quality control testing. For instance, laminated structures in which two pieces of like or unlike materials are bonded together by an adhesive can be checked for bond quality through holography. Even with a common laminate such as plywood it is difficult to discover the existence of unglued portions without tearing the structure apart. With laser beam photography, however, very small differences in the laminate thickness result in interference fringes in the holograph image. These indicate the presence of an unbonded area. There has in the past been a major drawback to this technique. For each laminate tested, the method had to be "calibrated" by checking a large number of known defective laminates. A new method circumvents much of the needed pretesting by considering the unbonded area to be a sort of membrane. In this way, theoretical knowledge of membrane deflection may be used in conjunction with a much reduced number of pretest experiments to determine the number of optical fringes that should appear for a given laminate. This information can then be directly related to the characteristics of unbonded areas. This method can be applied to any adhesive bonded facing that has membrane characteristics over unbonded areas. It allows prediction of the applicability of holographic testing with a minimum of experimental effort.

  • Supplemental Notes:
    • This article appeared in a publication Analytical Techniques: A Compilation.
  • Corporate Authors:

    National Aeronautics and Space Administration

    400 Maryland Avenue, SW
    Washington, DC  USA  20546
  • Authors:
    • Stuckenberg, F H
  • Publication Date: 1975-1

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Filing Info

  • Accession Number: 00128510
  • Record Type: Publication
  • Report/Paper Numbers: NASA CR-2028
  • Contract Numbers: MFS-24402, NPO-11612, MFS-16968
  • Files: TRIS
  • Created Date: Apr 21 1976 12:00AM