Structural damping in contacts and joints subjected to simultaneous action of normal and tangential vibrations (Relaxation damping)

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The present project is dedicated to the active control of structural damping, a problem that is both important and not yet satisfactorily solved in many areas of engineering. For example, some engineers involved in the design of the International Space Station report that, due to the weak structural damping of the ISS, astronauts work and live under permanent, heavy noise pollution. Due to the metal structure of the ISS and the absence of damping material, even small sources of noise tend to become a big problem, e.g. the noise of a small that would be barely noticeable on Earth. This problem remains unsolved since weight constraints preclude the use of heavy dampers. In such cases it can be useful to rely on structural damping, e.g. by taking advantage of contact friction. In this project we will attempt to control structural damping through frictional contacts - either using joints already present in the structure or contacts introduced for the specific purpose of damping control. Although joints with micro sliding make an important contribution to the damping of real structures, it is still not possible to accurately model and therefore control them. From our perspective, there are two reasons for this: On the one hand, problems of tangential contact with friction are particularly difficult mathematically - due to various non-linearities occurring in the contact and the complexity of the boundary conditions, which are unknown a priori and must be determined iteratively during the solution process. The other reason is that an important dissipation mechanism seems to have been overlooked in frictional contacts so far. This dissipation mechanism was recently proposed by us and is called "relaxation damping". Depending on the type of loading it may contribute significantly to the total dissipation, or even become the main dissipation mechanism. Of particular importance is that this damping can be controlled in a simple manner. The main objective of the project is a comprehensive experimental and theoretical study of relaxation damping in frictional contacts under simultaneous action of tangential and normal vibration. First the existing theory of relaxation damping will be verified experimentally, then further experimental studies will provide information about the relative contribution of relaxation damping compared to classic "Mindlin damping" and to internal losses in the material. Based on that, methods for the active control of structural damping through frictional contact will be developed and implemented. Experimental studies will be carried out by means of an experimental apparatus, which shall be designed and constructed as part of the project. From the obtained results, strategies for effective and low-wear structural damping will be developed and implemented for an example system.