Development of a Test Procedure for the Experimental Determination of the Static Friction Coefficient in Friction-Locked Connections for Mechanical and Plant Engineering

Short title: Haftreibungszahl Maschinenbau

Funding reference number: 01IF23636N

Project period: Jul 2025 – Dec 2027

Project budget: 228.681 €

Research focus:

Focus 2 (since 02/2024): Sustainable Objects, Urban Structures, Materials and Processes

Structural unit:

Faculty of Engineering

Project management:

Prof. Dr.-Ing. Ralf Glienke

Project supporter:

German Aerospace Center (DLR)

Funding:

Federal Ministry for Economic Affairs and Energy (BMWE)

At the top left, an inclined escalator structure with a visible side panel is shown. Next to it, at the top right, are technical drawings of various fasteners. At the bottom left, a test rig with multiple sensors and cables is displayed. To its right, there is a color-coded 3D surface analysis with microscopic structures. At the bottom right, a numerical simulation with color-coded stress distribution is shown. — From left to right: Use case (source: Wismar University of Applied Sciences/Prof. Glienke), connecting elements (source: IGP Rostock), testing device (source: Wismar University of Applied Sciences/Andreas Ebert), surface characterization (source: IGP Rostock), numerics (source: Wismar University of Applied Sciences/Melanie Hagemann).

The aim of the research project is to determine the sensitivity of existing factors influencing the static friction coefficient of slip-resistant preloaded connections.

The safe and economical design of mechanically joined connections is of great importance to companies due to the multiplier effect. In mechanical and plant engineering, the transverse forces occurring in a bolted connection must be transmitted by frictional locking in accordance with VDI 2230-1. Both the clamping force and the coefficient of static friction are included in the slip safety verification.

Since the coefficient of static friction can vary greatly depending on the design, only conservative values or ranges are specified in regulations. In the case of coated components, experimental investigations often have to be carried out. For the aforementioned industry, these can be carried out in accordance with EN 1090-2, whereby the procedure is geared towards steel construction and does not take into account the geometric diversity or complex load history in mechanical engineering.

Therefore, this project aims to develop a test procedure for determining the coefficient of static friction, taking into account the application-specific influencing factors of the connection. To this end, the coefficient of static friction is first determined on samples subjected to transverse forces using TBJ and TTJ. For a better understanding of the mechanisms, the surfaces are characterized and the pressure state is analyzed using FEM. The transferability of the results to more complex connections will be carried out using FEM and validated with corresponding experimental investigations. Among other things, different types of loads, load histories, connecting elements, and friction surface pretreatments will be investigated.

Based on the findings, taking into account the relevant influencing factors, an efficient test procedure for determining the static friction coefficient on small test specimens and a catalog of measures for optimization are derived, which in particular will save SMEs the trouble of developing individual test concepts in the future and enable the transferability of the results.