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Laboratory for material and joining technology (LWF)
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Completion of the research project

The IGF project IGF No.: 18895 N (duration 01.12.2015 - 31.05.2018) was funded by the Forschungsvereinigung Stahlanwendung e. V. (FOSTA) and in cooperation with the Laboratory for Material and Joining Technology (LWF Paderborn) and the Institute of Mechanics (IfM Kassel).

In the processing of heat-curing adhesives in the large-scale production of the automotive industry, the adhesive seams within the steel-intensive mixed structure (car body) consisting of individual components and to be joined are cured in a cataphoretic dip-paint bath (KTL) together with the corrosion-protective paint. The cataphoretic curing of bonded seams requires an upstream process for fixing the components after adhesive application, which stabilizes the still soft structure after adhesive application and joining. This necessary "handling stiffness and strength" is often achieved in bonded steel composite structures by additional mechanical joining points, which are inserted at a fixed distance (hybrid joining). The strains and displacements that occur during the heat treatment of hybrid joined structures result in stresses that can lead to damage in the joining area in the form of boundary layer failure or cohesion fractures.

The aim of the project was the development of a calculation and evaluation method with which the damage-relevant stresses of the joint can be determined as a function of the material, geometrical and process-related influencing variables. For this purpose, a numerical calculation method as well as a simple test method with an associated "rule of thumb" was developed, with which the suitability of adhesives for the cathodic dip coating process can be evaluated comparatively in steel-intensive mixed structures. The improvement of material, geometrical and process engineering parameters leads to an optimal lightweight construction. The calculation methods and optimisation possibilities shown here enable steel users to avoid damage to the bonded joint due to temperature loads and the resulting relative displacement of the joined parts during the hardening process.

The IGF project "Method development for the simulation of the thermomechanical behaviour of adhesive layers in hybrid joints during the hardening process", IGF project no. 18895 N of the Forschungsvereinigung Stahlanwendung e. V. (FOSTA), Sohnstraße 65, 40237 Düsseldorf was funded via the AiF within the framework of the programme for the promotion of joint industrial research (IGF) by the Federal Ministry of Economics and Energy on the basis of a resolution of the German Bundestag. We would like to take this opportunity to thank them for their support. We would also like to thank the members of the project support committee for the experimental materials, auxiliary joining elements and services provided for the implementation of this research project as well as for their support and constructive discussions.

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