The construction of dynamically loaded metallic materials and components is usually based on the relation between the stress amplitude and the number of cycles to failure, which is displayed in S-N curves. For this reason, the generation of S-N curves, for which a minimum number of 20 tests is recommended according to DIN 50100:2022-12, is of great importance. Statistical statements regarding the probability of fracture or failure result in a significantly improved lifetime prediction, whereas the increased number of tests and the associated experimental effort lead to increased costs. A new lifetime prediction method (LPV) is being developed to bridge the gap between statistically verified lifetime predictions and the resulting increase in time and costs. The lifetime prediction method StressLife, which is characterized by S-N curves in the high cycle fatigue (HCF) range based on data from a small number of fatigue tests, serves as the basis for the new development method. The material reactions from just one load increase test and two constant amplitude tests are determined by using different NDT measurement procedures (e. g. optical strain measurement and electric resistance measurement) and used as an input variable for the LPV. The method to be developed contains fundamental extensions and unique selling points compared to existing methods with regard to two aspects. The first aspect is the systematic investigation and integration of statistical procedures, which makes it possible to estimate different fracture and failure probabilities. The second aspect includes the consideration of data from notched fatigue tests, which can provide notched S-N curves with reduced testing effort and thus provide an initial approach with regard to a component S-N curve.

The method development is carried out on the model material C45E, which is available in two different heat threatment states (annealed and tempered). Comprehensive fatigue tests are carried out using the StressLife method for process development with the steel C45E in two heat treatment conditions. Two different notched geometries are used, which differ in terms of their notch shape numbers.  For the statistical analysis, the primary focus is on recording the scatter due to the small sample size in the LPV. Parametric and non-parametric test methods are used for the density estimation.

The aim of the proposed research project is to develop a lifetime prediction method that enables the most accurate prognosis possible with regard to cyclic deformation behaviour and (residual) fatigue life despite a reduced specimen effort. Since multiaxial stress states occur in the case of notched specimens under stress, this approach can also be transferred to demonstrator or component tests, thereby creating a wide field of application for future use.