Vibration resistance of surface-hardened components and ultra-high-strength steels

In this work, methods were developed to calculate the fatigue strength of high- and ultra-high strength steels as well as of surface-hardened components. Using various experimental investigations of different materials, methods of the FKM-Guideline Nonlinear were adapted to determine the cyclic material behaviour of high- and ultra-high strength steels on the basis of quasi-static material properties. For this, methods were extended to allow the estimation of the cyclic stress-strain curve, the mean-stress sensitivity as well as damage parameter life curves based on the ultimate tensile strength. Furthermore, methods were developed to allow an assessment of structural durability on the basis of the local strain approach for surface-hardened components. Since the failure of these components can originate from both the notch root as well as the transition area between the low-strength core material and the high-strength surface layer due to the inhomogeneous material properties and the residual stresses present, the proof of structural durability of the FKM-Nonlinear Guideline was adapted. The algorithms of the local strain approach were extended to include a so-called two-point assessment and the consideration of residual stresses. An approximation method for estimating the elastic-plastic stresses at both assessment points was also developed.