Modeling of Mechanical Interfaces in a Systems Context

The behavior of a technical system depends on the properties of the subsystems and their physical interaction. The interactions take place at interfaces, which may be characterized as conformal or non-conformal depending on how close the mating surfaces fit together. Engineering surfaces are more or less randomly rough. Contact between rough surfaces is, in general, discontinuous and the real area of contact is a small fraction of the nominal contact area. The influence from roughness increases with the roughness-to-normal load ratio, which normally is significantly higher for conformal interfaces than for non-conformal. The topography of interacting conformal surfaces, as for example in bolted joints, has often a significant influence on the physical behavior of the entire system. Optimization of shape and surface properties of conformal interfaces is thus of vital importance in engineering design of many technical systems. In modularized products, it is of strategic importance. FE modeling of solid bodies is a relatively straightforward technique. Proper modeling of the interaction between the bodies is not straightforward. A method to model the physical behavior of technical systems with a mixture of conformal and non-conformal interfaces is presented. The basic approach is to aggregate mix-fidelity systems models from condensed submodels and to connect them with interface feature models. The parameters describing the properties of an interface feature is obtained directly from characteristic design properties such as shape, material, and surface roughness, or alternatively as a solution to an inverse problem. The modeling method is illustrated with a design scenario for a parallel-kinematics machine.

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