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An analytical and experimental investigation was undertaken to determine if the adhesive debond initiation stress could be predicted for arbitrary joint geometries. The analysis was based upon a threshold total strain-energy-release rate (Gth) concept. Two bonded systems were tested: T300/5208 graphite/epoxy adherends bonded with either EC-3445 or FM-300 adhesive. The Gth for each adhesive was determined from cracked-lap-shear (CLS) specimens by debond initiation tests. Finite-element analyses of various tapered CLS specimen geometries predicted the specimen stress at which the total strain-energy-release rate (GT) equaled Gth at the joint tip. Experiments verified the predictions. The approach described herein predicts the maximum stress at which an adhesive joint can be cycled yet not debond. Total strain-energy-release rate appeared to be the driving parameter for cyclic debonding and debond initiation in structural adhesives, and debond initiation and growth were found to occur with virtually no peel stress present.
adhesive joints, design, debond propagation, strain-energy-release rate, fracture mechanics
NASA-Langley Research Center, Hampton, VA
Associate Professor, University of MaineUniversity of Missouri, OronoRolla, ME