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X-Ray Diffraction Evaluation of Adhesive Bonds and Stress Measurement With Diffracting Paint

Published online by Cambridge University Press:  06 March 2019

Charles S. Barrett  and
Paul Predecki
Charles S. Barrett
Affiliation:
University of Denver Research Institute, Denver, Colorado 80208
Paul Predecki
Affiliation:
University of Denver Research Institute, Denver, Colorado 80208
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Abstract

X-ray diffraction is found effective in disclosing the distribution of stresses over the surface of adhesively bonded lap joints when loads well below the yield point are applied. When a pair of 6061-T6 aluminum strips 1/16” or 1/32” thick and 3/4” wide is adhesively bonded in a single lap joint and loaded in tension, maps giving the distribution of the X-ray-measured stresses show the limits of the bonded area with an accuracy about equal to the width (1 mm) cf the irradiated area along the specimen. Attendant bending stresses resulting from the loading are also registered. Stress values can be obtained from the observed diffraction angles by calibration with tensile tests of a single unbonded strip. Similar results are obtained for graphite/epoxy laminates adhesively bonded in a single lap joint to aluminum when diffraction is from the aluminum, but a lower accuracy is obtained when diffraction is from the filled composite.

Another X-ray method was developed for measuring applied (not pre-existing residual) stresses, and for mapping their distribution around a joint. A thin layer of epoxy paint containing a diffracting filler (say aluminum or silver powder) is applied to a specimen and cured. Diffraction from this paint yields shifts in diffraction angle approximately proportional to the magnitude of applied stresses. The limits of the bonded area in single lap joints under load are disclosed. Both methods appear, therefore, to be practicable for mapping the areas that are properly bonded, and presumably also for non-destructive evaluation of bond defects.

Type
Research Article
Information
Advances in X-Ray Analysis , Volume 24: Twenty-Ninth Annual Conference on Applications of X-ray Analysis, August 4-8, 1980 , 1980 , pp. 231 - 238
Copyright
Copyright © International Centre for Diffraction Data 1980

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References

1. Barrett, C. S. and Predecki, Paul, Stress Measurement in Polymeric Materials by X-Ray Diffraction, Polymer Eng. & Sci. 16:602 (1976).Google Scholar
2. Fredecki, Paul and Barrett, Charles S., Stress Measurement in Graphite/Epoxy Composites by X-Ray Diffraction from Fillers, J. Conp. Mat. 13:61–71 (1979).Google Scholar
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