Reliable modeling and characterization of joints

Joining and Joints

We characterize the mechanical properties of joints and assess them in terms of their deformation and failure behavior. A particular focus of our work is joint modeling for crash simulations, as this is the only way to analyze such a large number of different joints in the whole vehicle structure, thousands of them, and predict their capacity. Work is also carried out on predicting residual stresses and distortion in thermal joints with the aid of numerical welding simulations. By simulating joining processes such as punch riveting we are able to determine the aspects of the process that influence the joint properties.


Characterization of the mechanical properties of joints and joined components

Deformation and failure modeling for joints

Investigations into damage and fracture mechanisms

Development of substitute modeling methods for joints in crash simulations

Characterization and modeling of joint failure (spot welds, laser welds, punch rivets and adhesive bonds) under crash conditions

Assessment and optimization of factors influencing a process with joint process simulations for punch riveting, welding etc.

Calculation of residual stress and distortion after welding with the aid of numerical welding simulations



Substitute modeling for crash simulations


A reliable and practical description of joint failure in crash simulations depends on special elements, so-called substitute models and their input data. The Fraunhofer IWM has developed a simple, efficient substitute model and a technique for determining the failure parameters for spot welds. A material model has also been implemented for modeling the failure of adhesive bonds with parameters that have been determined from substance and joint samples and ...




Modeling the deformation and failure of spot welds in hot-formed high carbon steels


The development of new high strength steels for use by the automotive industry has created the potential for lightweight designs that combine thin walls and low weight with high strength, rigidity and passive safety. So-called softening zones form when welding hot-formed, 22MnB5 boron alloy steels; these zones are much weaker than the surrounding material. The effect of ...




Advanced substitute model for punch rivets joints


Mechanical joining techniques have the advantage that they can be used to join different types of materials in a safe process, without the negative effects of heat on the material properties. A number of mechanical joining techniques, such as semi-tubular punch rivets and direct screw joints are therefore used on multi-material mixes in automobile manufacturing. Until now, there has been a lack of simulation models and characteristic joint data that would ...




Modelling of adhesive joints

By avoiding local stress concentrations, adhesive joining can offer advantages in light-weight structures compared to mechanical fasteners. For a reliable component design the load carrying capacity and failure behavior of the adhesive joint has to be understood and simulation methods are required to be as accurate and as efficient as possible. Cohesive zone models are often used to meet both requirements. In order to provide the necessary material behavior data, scientists at the Fraunhofer IWM experimentally characterize adhesive joints, which can account for additional effects such as loading rate, temperature and humidity. Local details may furthermore be studied by high-discretization continuum mechanics modelling of the deformation and damage behavior, which can be included into the component modelling.


Calculation of welding residual stress and distortion


The heterogeneous nature of welding in which the material is heated up locally and cools down induces internal stresses and leads to component distortion. This has a negative effect on component quality and functionality and can also cause damage, e.g cracks, and/or reduce the service life. Internal stress and distortion are closely related, and many factors lead to their generation. The material properties, clamping conditions as well as ...



Publications regarding Joining and Joints

Contributions to newspapers, books and conferences as well as dissertations and project reports...