Fatigue Strength Assessment of Elastic Couplings under Rotating Loads Using FKM Guideline

• Analytics & Modeling - Digital Twin / Simulation
• Sensors - Haptic Sensors

• Equipment & Machinery
• Metals

• Logistics & Transportation
• Procurement

• Manufacturing Process Simulation
• Virtual Reality

Elastic couplings, frequently used in industries like automobile, power, and manufacturing, present a unique challenge due to their nonlinear characteristics, relative rotation, and large cycle number of the radial load. These peculiarities do not allow the usage of the superposition principle of loads, meaning that every possible combination of loads (axial force, radial force, and torsional torque) must be separately considered. This results in a large number of load cases and consequently a large number of strength assessments. The simple assessment of the superimposed stress states, resulting from a single unit load, would lead to false results, possibly showing a higher component strength than in reality, which could result in a failure of the part. Therefore, all load combinations must be simulated and subsequently assessed against the fatigue strength accordingly.

The customer in this case study is Süddeutsche Gelenkscheibenfabrik GmbH & Co. KG (SGF), a German company that specializes in the production of elastic couplings. These couplings are used in a variety of industries, including automobile, power, and manufacturing. The elastic couplings of SGF are designed to reduce vibrations and compensate for axis misalignment, while simultaneously improving the fatigue strength of the complete machine. However, the company faced a challenge in assessing the fatigue strength of the metal parts of these couplings due to their nonlinear characteristics and the large cycle number of the radial load.

The solution to this challenge involves a three-step method. First, the actual forces and torques applied to the metal flanges resulting from the loads on the coupling are determined by means of a multibody simulation for every possible load combination. These forces and torques are then transferred to a FEM analysis in the second step to determine the stress states for each load combination. In the third step, the appropriate load combinations are determined and a static and fatigue strength assessment according to the FKM guideline is conducted with S-Life FKM. The MSC Marc FEM software is used to perform the FEM analyses due to the simple table-driven load definition. With this approach, all possible load combinations are compiled in tables, one for each force and torque direction respectively. All possible load combinations are therefore simulated by a single FEM-load case with the usage of such tables. The transfer of forces and torques from the MBS software to MSC Marc is done with the help of scripts, resulting in a very simple and fast process for the first two steps of the strength assessment.

• The implementation of the three-step method using the MSC Marc FEM software and S-Life FKM has streamlined the process of assessing the fatigue strength of the metal parts of the elastic couplings. The method has simplified the process of determining the actual forces and torques applied to the metal flanges, transferring these to a FEM analysis, and conducting a static and fatigue strength assessment according to the FKM guideline. This has not only reduced the time and effort required by the engineers but also minimized the potential for errors and misinterpretations of the results. Furthermore, the method has improved the accuracy of the fatigue strength assessment, providing a more reliable prediction of the fatigue strength of the metal parts of the coupling.

• Reduction in the number of load cases and strength assessments by considering all possible load combinations in a single FEM-load case.
• Significant reduction in the engineer’s time and interaction required for the simulation procedure.
• Minimization of possible errors and misinterpretations of the results.