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The Effect of Cure Cycle Time on the Properties of Epoxy-Bonded Joints

Abstract This paper presents the results of the study of the properties of epoxy-bonded joints. Depending on the parameters of cure cycles the epoxy adhesive film has got various mechanical properties. When it is possible to use cure parameters suggested in the data sheet of the adhesive film the best results are obtained. However, in aerospace applications the cure cycle depends on the thermal resistance of other aircraft elements including electrical equipment, cables, etc., and is different from the recommended in the data sheet. Composite Patch Bonded Repair (CPBR) is a special methodology, where the patch cure cycle and the bonding process must be carried out in one operation. The adhesive film cure cycle parameters depend on the prepreg cure cycle parameters. The purpose of this research is to define the influence of a prolonged cure cycle of the adhesive film on the bonded layer strength properties. The metal surface of the specimen has been prepared for bonding by sandblasting and the use of Corrosion Inhibiting Primer BR 127. The tests were performed with the use of Structural Adhesive Film AF 163-2 and two types of cure cycles: the cycle recommended by the data sheet - 121ºC/60 min and the prolonged one - 121ºC/105 min. After the cure cycle the thickness of the bonded layer was measured. Both specimens were comparatively tested during the following strength tests of the bonded layer: static breaking tests using the wedge and the shear strength investigations. The surface of the bonded layer was observed during the tests by an electronic microscope (100x, 200x), which made it possible to demonstrate the effect of the cure cycle on the porosity and observe the nature of the bonded layer damage - de-cohesive and de-adhesive.