Observations in the structural response of adhesive bondline defects

In terms of adhesively bonded repairs there are two main concerns with regard to structural integrity. These are the effect of debonds and weak bondlines on the load transfer and durability of the joint. The influence of load transfer depends on the stiffness of the bondline. When this is degraded the out-of-plane deformation of the joint will be modified locally. Observation of the out-of-plane deformation is a key in the identification of weakened bondline and represents an indication that either poor surface preparation or aging effects have occurred. Holographic interferometry has been used to better understand the structural response of bondline defects, both debonds and weak bonds. The interferogram fringe patterns show the structural response and indicate whether the bondline has been broken or is weakly bonded. The significance of this observation is that weak bonds do affect the structural load response of the bondline in a number of ways. This effect is due to the reduction in bondline stiffness. © 1999 Elsevier Science Ltd. All rights reserved.