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The Effect of FM-73 Cure Temperature on the Durability of Bonded Joints Employing BR127 Printer

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Bonded repairs to aircraft structure employing composite patches, may generate significant levels of residual stress in the repaired structure. This is due to the difference in the coefficient of thermal expansion between the repair material and the parent structure. One way of minimising the level of residual stress is to cure the repair adhesive at the lowest possible temperature. FM-73 is a fracture tough adhesive used in bonded repairs that is typically cured at 12OC for 1 hour. However, a cure cycle of 8OC for 8 hours may be employed in critical applications. The durability of bonds formed between aluminium and FM-73 epoxy adhesive using the two cure cycles mentioned has been examined. Al-2024 T3 unclad alloy was pretreated either using the RAAF standard gritblast and silane process or with the gritblast silane process followed by application of BR-127 chromate primer. Results suggest that whilst the addition of BR-i 27 primer improves bond durability for the adhesive cured at 120C, there is little improvement observed for the adhesive cured at 80C. Fracture analysis of failed wedge samples using SEM and surface analysis equipment indicate a change in the locus of fracture for the two cure cycles employed and a possible change in the fracture mechanism. Analysis of bonded samples in cross-section suggest that the interfacial region is wider for the 120C cured sample. This result may suggest that processes such as interdiffusion of the primer and adhesive layers are important factors governing bond durability of adhesive joints.

Subject Categories:

  • Bombers
  • Adhesives, Seals and Binders
  • Laminates and Composite Materials

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