Simulation of the mode of failure and application of micro capsules in adhesives for premature damage detection

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The joining by the application of adhesives has many advantages over other joining techniques. Thereforeadhesive bonding has become a significant part in key industries like automotive engineering and mechanicalengineering. An important issue when dealing with bonded structures is the verification of safety relevantfactors like the strength of the joint and the ageing behavior. This detection is nonetheless strongly limitedsince many test procedures belong to destructive inspection methods, and also non-destructive inspectionswhich are most often conducted during the fabrication process do not deliver any information about the lifeexpectancy of stressed components.The application of adhesives which contain microcapsules filled with dyes as visual markers can readily enablethe detection of deterioration in the adhesive layer: If a crack occurs the micro capsule is also damaged andthe incorporated detectable dye is released. The crack propagation is strongly influenced by theinhomogeneities (micro capsules) in the bond line. Therefore, a main target of this research project is themechanical deterioration simulation of the origin of incipient cracks and the crack propagation in thethree-dimensional network of the adhesive. In addition, the evalution of simulation parameters will be crucial.For the observation of the crack growth systems of transparent substrate materials (e.g. cycloolefine copolymer and polycarbonate) and transparent adhesives polymers like epoxy resins, silicons, acrylates, andpolyurethanes, respectively, will be applied. The required micro capsules are prepared by means of interfacial polymerisation and are characterized in terms of morphology, wall thickness, and particle size distribution. Byvariation of reaction conditions and starting material different capsule parameters can bhe achieved. These capsules will form the basis for the subsequent review of simulation results.