Cohesive zone models (CZM) and more for the automotive industry

For the simulation of adhesively bonded joints, a suitably selected material model is required on the one hand, and experimentally determined model parameters for the specific adhesive on the other. Based on this, Fraunhofer IFAM determines material cards for adhesives. The institute has many years of experience, particularly in the field of cohesive zone models (CZM) in the automotive industry, and can suggest models and suitable experiments or develop them further if required.

Crash safety for the automotive industry through simulation of adhesive bonds

The calculation or simulation of adhesively bonded joints is of great importance, especially in the automotive industry. Above all, cohesive zone models (CZM) have been indispensable for crash simulation in this area since they were established in the German automotive industry in the early 2000s with the participation of our experts. Fraunhofer IFAM has extensive expertise in this area. Finite element software offers cohesive zone models in variants with different levels of complexity, which differ, for example, in terms of strain rate dependence and require different levels of testing for material card determination. Depending on the individual application, we advise you on the selection of model variants and suitable experiments.

Experiments for material card determination

To determine model parameters, Fraunhofer IFAM carries out a wide variety of experiments in its test laboratory, e.g.:

• Tensile test to determine the elastic behavior
• Butt joint tensile test and thick adherend shear test, determination of strengths in tension and shear
• Fracture mechanical tests to determine the critical energy release rates in Mode I and Mode II or III
  • Mode I: TDCB (tapered double cantilever beam) for structural adhesives, DCB (double cantilever beam) with rotation measurement for elastic adhesively bonded joints
  • Mode II e.g. TENF (tapered end notched flexure)
• Experiments performed at different test velocities and temperatures

If one wishes to apply the established cohesive zone models to new material classes, it is usually necessary to adapt or further develop the experiments used for material card determination. An example of this is the experiment developed at Fraunhofer IFAM to determine the critical energy release rate in Mode III of flexible polyurethane adhesives.

Validation of the material card

A material card determination can be complemented by a validation to assess the accuracy of a simulation of adhesively bonded joints with the material card. For this purpose, we carry out a test on an adhesive joint or a bonded component and, for comparison, an FE simulation of the experiment. As an example, the adjacent figure shows a so-called T-joint specimen, which was used as a relatively complex validation specimen with three strongly stressed bonded joints in several AiF projects as well as in work carried out directly for adhesive or automotive manufacturers.

If you want to build up your own know-how for the simulation of adhesively bonded joints, a project with material card determination for a specific adhesive and validation is the ideal way for you - feel free to contact us!