X-Ray Diffraction Evaluation of Adhesive Bonds and Damage in Composites
Stresses can be measured by X-ray diffraction, not only in metals but also in polymeric composites containing some crystalline filler particles. Diffraction is found effective in disclosing the distribution of stresses over the surface of adhesively bonded joints in aluminum strips when loads well below the yield point are applied. When two 6061-T6 aluminum strips 1/16" or 1/32" thick and 3/4" wide are adhesively bonded in a single lap joint and loaded in tension, maps giving the distribution of the X-ray-measured stresses show clear evidence of the way in which stresses are transferred from one adherend to the other. The maps show the limits of the bonded area with an accuracy about equal to the width (1 mm) of 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 to aluminum when diffraction is from the aluminum, but a much lower accuracy was obtained when diffraction was from the filled composite.