Novel Approach for Endurance Testing of Riblet-Structured Thin Sheets Under Realistic Loading Conditions in Active Drag-Reduction Systems

摘要

A novel fatigue testing device for bending loading was developed that resembles loading conditions in aerodynamic drag-reduction systems, creating transversal surface waves to modify the surfaces' turbulent boundary layer. The setup uses Lorentz force actuators and is employed in fully reversed loading (R= -1) at a testing frequency of around 100 Hz. Tests were run on riblet-structured Alclad 2024 T351 material. The damage mechanisms for this material are found to be similar for axial and flexural loading. In the high cycle fatigue regime up to a few 106 load cycles, the S/N-curves are also comparable for both loading modes. One distinct difference between the loading modes is a less pronounced threshold behavior in the S/N-curve for bending. Furthermore, a higher stress level has to be applied for fatigue failure in this case.