The central feature of the services offered by the Fraunhofer IFAM for adhesive bonding is optimum design of the bonded joint in accordance with the specific needs of the customer. If the requirements are known, the best possible joint is identified following a series of harmonised development stages.
The design starts with a decision: whether to select a highly flexible, rubber-elastic adhesive or opt for a more rigid, elastic-plastic adhesive. The strength of the bonded joint is determined in tests: What forces have to be applied to destroy the bond? The nature of the bond break yields further information for the design. With a »cohesive break« the damage occurs in the bond layer, meaning that the strength of the adhesive is decisive for the strength of the joint. With a »boundary layer break«, the failure occurs in the thin boundary layer between the bonded component and adhesive, which is only a few thousands of a millimetre thick. Numerous tests are carried out to determine the failure behaviour under different conditions, for example at different temperatures. The so obtained information defines various failure criteria and allows computer simulations to be carried out which identify critical zones – socalled hot-spots.
The combination of simulation work and the verification by load testing allows the limits of a joint to be ascertained. This methodology results in the design of a bonded joint that is tailored to withstand the required strains and stresses and fully meets the requirements of the application. The composition and geometry of the joint components and the production conditions are also taken into account here.