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In the manufacture of foam core sandwich structures, the faces are bonded to the core, and blocks of foam core material are bonded to each other in order to obtain the required thickness. Core material blocks are also joined lengthwise in the production of large and/or curved structures, using so called butt joints. However, in the manufacturing process, flaws may occur. Debonding in the adhesive joints acts as cracks, and sharp corners will be the result of an absence of filler material in a butt joint. The present paper deals with methods for the prediction of the reduction in load-bearing capacity of foam core sandwich beams due to these flaws. A fracture mechanics approach is used, including both analytical methods and finite element analysis. Fracture toughness data of the materials and wedge geometries are found from simple specimens. Full-scale tests are performed using beams with prefabricated flaws for verifying the analysis. The predictions agree well with the experimental results. The reduction in load-bearing capacity is as much as between a factor of 1.5 to 4.9 for different geometries and flaw types.
sandwich constructions, cellular foam core, polyvinyl chloride, damage, debonding, butt joint, fracture, stress intensity, fracture toughness, bimaterial crack, bimaterial wedge, finite element analysis
The Royal Institute of Technology, Stockholm,