Mechanical Behaviour of Single-Layer Adhesive Joints : an integrated approach

Sammanfattning: Innovative products that are competitive on the market are likely to employ newtypes of materials and unusual geometries. A method that can assemble dissimilarmaterials and irregular geometries cost-effectively and at the same time offera joint that is light in weight and imperceptible, is optimal. Conventional joiningmethods, such as welding and riveting, can no longer satisfy the joining purposecompletely. Adhesive joints satisfy all mentioned requirements above and henceoffer design engineers a wider choice of materials and an increased freedom ingeometry design of the components, which most likely leads to a better design ina shorter time. The prediction of the mechanical behaviour of a joint, preferablywith simple and efficient formulas, plays an important role in the product designprocess. In this thesis, single-layer adhesive joints are analysed through the integratedapproach, i.e. an extensive stress analysis followed by a fracture analysisto determine the energy release rate and the mode-mixity due to general endloads. The purpose is to provide easy-to-use design formulas and to investigatedifferent specimen configurations for the experimental determination of the mechanicalproperties of adhesives under mixed mode loading.In the stress analysis, a systematic and easy to use closed-form solution based onthe beam/adhesive layer (B/A) model is presented to determine the stress andstrain in a linear elastic single-layer adhesive joint. In the fracture analysis, fourtypes of single-layer adhesive joints are investigated based on the closed-formsolution given in the stress analysis. The B/A model is compared to two continuummodels: one neglecting the existence of the adhesive layer (Suo and Hutchinson1990) and the other accounting the adhesive layer by the use of FEM.The results of the B/A model compares favourably to the FE-analyses. Threetypes of basic loading systems are identified for the symmetric semi-infinitejoint geometry. Two specimens for testing mode mixity are suggested. Accordingto the theoretical studies by use of the B/A model, the specimen denoted theMixed Mode B with a short crack length offers good flexibility, variety and stability.