27 th ICAF Symposium – Jerusalem, 5 – 7 June 2013 Fatigue Disbonding of Bonded Repairs – An Application of the Strain Energy Approach J.A. Pascoe 1,* , C.D. Rans 1,2 , R.C. Alderliesten 1 , R. Benedictus 1 1 Structural Integrity & Composites Group, Faculty of Aerospace Engineering, Delft University of Technology, P.O. Box 5058, 2600 GB Delft, The Netherlands 2 Department of Mechanical & Aerospace Engineering, Carleton University, 1125 Colonel By Dr, K1S 5B6 Ottawa, ON, Canada *Corresponding author: j.a.pascoe@tudelft.nl Abstract: A model was developed to predict disbond growth due to constant amplitude fatigue loading in a simple bonded repair configuration. The model uses a Paris relation to relate disbond growth to the strain energy release rate (SERR), which is calculated numerically as a function of the disbond length. An iterative combination of these two relations allows the prediction of the disbond length. The model appears promising, but problems with the experimental data prevented a full validation. INTRODUCTION Small damages in plate structures are commonly repaired with a patch repair. Traditionally these are fastened using rivets. This requires the drilling of holes in the structure. Together with the load transfer in the form of point loads through the rivets, this results in large stress concentrations. Adhesive bonding of the repair patches does not require holes and results in a more uniform load transfer, greatly reducing the stress concentrations. These advantages have led to some applications of bonded repairs, pioneered by the Royal Australian Air Force [1]. However a lack of understanding of the damage tolerance behaviour of these bonded joints is one of the important factors preventing wider application. One damage mode that is of particular concern is that of disbonding; the separation of the patch from the substrate. A damage mode which is very similar to the damage mode of inter-ply delamination in composite structures Three approaches have been identified for dealing with this damage mode and certifying bonded repairs: no-growth [2, 3], large damage carrying capacity (LDCC) and slow- growth [3]. Each approach employs a different philosophy for ensuring safety. In the no-growth approach safety is ensured by demonstrating that plausible in- service damages can be sustained and will not grow due to the loading encountered over the entire service life of the structure. This is typically demonstrated through