Untersuchungen zum Einfluss der Bauteiloberfläche und -randschicht auf die Ermüdungsfestigkeit

FKM 2005
Issue number 286
Project no. 257

Final report
Abstract:

To experimentally investigate the influence of the surface layer on the fatigue strength, selector tests were carried out on unnotched test specimens in which the surface roughness and the notch radius of the turning depths vary. The surface hardening as an influencing parameter was not specifically varied. Normal stresses (4-point bending) were realized as stresses. As part of this research project, 20 test series with six different surface topographies were investigated for three steel and two ductile iron materials. Both the fatigue strength curve and the fatigue strength were determined in single-stage tests. For the influence of the surface topography, the surface factor according to the guideline, the FKM guideline and a new proposal by J. Liu were examined. The comparison with the experimental results of the investigation shows that the results of the test series cannot be described by these factors. The residual stresses after machining were determined radiographically in the longitudinal and circumferential direction of the specimen. Different strength hypotheses were used to evaluate the residual stresses. The influence of the microstructure and the strength could not be quantified further. The calculation proposal by J. Liu does not describe the reduction in fatigue strength due to the influence of the surface significantly better than the previous calculation models, despite the additional parameter surface shape number K o (in addition to roughness). However, it should be pursued further, as the introduction of a surface shape number is appropriate for other roughness profiles, such as those produced during grinding. The influence of the surface on the fatigue strength can only be described if the residual stress state is taken into account. From the results of this investigation, a concept can be proposed with which the fatigue strength can be accurately calculated if the static strength, the surface topography and the residual stresses are known. The objective of the research project was achieved.
Scope of report:
227 pages, 187 illustrations, 71 tables, 106 references
Start of work:
April 01, 2002
End of work:
September 30, 2004
Funding body:
BMWA / AiF-No. 13247 ßG/1 Research institutions: Institute for Mechanical Plant Engineering and Structural Durability (IMAB) Clausthal University of Technology Prof. Dr.-lng. A. Esderts Prof. Dr.-lng. H. Zenner Dipl.-lng. U. Kleemann Institute for Surface Technology and Production Metrology (IOF) Dresden University of Technology Prof. Dr.-lng. U. Günther Dr.-lng. A. Popp
Chairman of the project:
Dr.-lng. H. Waltermann Barmag/Saurer GmbH chstadt