Contact mechanics

Aim is the description of the normal and tangential contact behavior of metal surfaces by constitutive contact laws which are suitable for the application in numerical simulation tools like the finite element method.
Starting point is the measurement, description and characterisation of rough surfaces at the micro scale and the subsequent simulation of the deformation behavior of the surface rough roughness by an elasto-plastic halfspace model, which takes into account lubrication and coatings.
From the halfspace simulations, constitutive contact laws can be identified, whih represent the homogenized behavior on the macroscale and can be experimentally verified at this scale.

Applications can be found in forming simulations, the modelling of energy dissipation in joints and the simulation of lamination stacks in electrical machines.


Constitutive friction law for the description and optimization of tailored surfaces

A central challenge in sheet-bulk metal forming is a partially uncontrolled material flow. This worsens the achievable geometrical accuracy of the parts. In this context, the objective of the project is to control the material flow by local adjustments of the friction by modifying the workpiece or tool surface. Hereby, the die filling of the functional elements is improved. Especially tool-sided modifications have a high potential, since they do not extend the process chain. However, for an efficient application, they must offer a high wear resistance, which is why the functional relationships between wear-induced changes in the tool topography and friction are being researched.

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A coupled MD-FE simulation method accounting for interphases in nanoparticle filled thermoplastics.

This proposal aims at an extension of a recently developed, hybrid MD-FE simulation scheme towards its application to materials dominated by polymer-solid interphases. Only particle-based methods are able to intrinsically resolve microstructure and mechanical behavior of interphases. Therefore, we proceed with the following setup: A coarse-grained MD domain, which contains a single nanoparticle and as much polymer as necessary to ensure bulk behavior at the boundary, is included into a FE do-main. The FE boundary is used to apply various types of deformations and to record the overall stress responses of particle, surrounding interphase and bulk. With these data, the parameters of a purely continuous counterpart to the hybrid setup are iteratively adjusted until it behaves identically. As its main feature, the continuous ersatz-model substitutes the interphase between particle and polymer by an interface governed by a surface energy in the sense of Gibbs. This can be understood as a condensation of micro-scale property profiles within the 3-D interphase into a 2-D continuum mechanical model. Ultimately, after homogenizing the continuous ersatzmodel, macroscopic structure simulations allowing for a due consideration of interphase effects as occurring around nanoparticles are to be realized.

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Reduced order modelling of non-linear gyroscopic systems in ALE formulation with frictional contact

Rotating systems are subject to gyroscopic effects, which influence the structure’s dynamics. The Arbitrary-Lagrangian-Eulerian formulation in the finite element method offers an efficient way to include translational and rotatory guiding movement in the model in the course of decoupling this motion from the FE mesh. At the same time this approach aggravates the computation of frictional contact of the rotating body with other still-standing structures.
This procedure stems from the…

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Material modelling of sheet-layered lamination stacks

The numerical simulation of sheet-layered lamination stacks, which can be found in electric motors and transformers, is a challenging task in structural mechanics due to the layout of these components.  Depending on the manufacturing process, these sheets are either in frictional contact to each other or are linked together with the help of a bonding varnish. Especially the interlayer between individual sheets and their interaction have a strong influence on the structure and may be responsible for a nonlinear deformation behavior. In the context of performance and computational effort, it is desirable to avoid a full Finite-Element simulation incorporating every layer such that homogenization techniques are used in this project to derive a sophisticated surrogate material model, which takes the special micro-structure of these lamination stacks into account.

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