EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Cracks in components are subjected to crack-closure-mechanisms that affect the build-up of the relevant stress intensity range threshold during cyclic loading. These mechanisms are essential for crack propagation under service loads in mechanical engineering applications. Such varying load ratios enforce an appropriate change of the long crack threshold value, thus leading to stress ratio depended resistance curves incorporating the build-up of crack-closure-mechanisms. It should be noted that an extensive number of crack propagation experiments is required to gain statistically evaluable fracture mechanical parameters for a specific material.
In the present work a generalized dataset to describe the formation of crack-closure-mechanisms is developed for the cast steel G21Mn5+N. Numerous crack propagation experiments covering a stress range from alternate to tumescent are conducted and a generalized resistance curve is derived statistically, which allows the description of the build-up of effects on the crack propagation rate uniformly for varying load ratios. The effect of initial pre-cracking by compressive loading on the fracture parameters is also studied.
Furthermore, the approach according to Newman is implemented to derive the respective long crack threshold value for arbitrary load ratios. Thus, a generalized dataset for crack-propagation studies considering closure-effects for G21Mn5+N is maintained by statistical evaluation.
To validate the aforementioned dataset, analytical fracture mechanical calculations invoking a modified NASGRO equation are conducted for the utilized SENB-sample geometries. A sound correlation of analytical and experimental crack propagation rates is observed.
The analytically derived fatigue life calculations show slightly conservative predictions of the experimental fatigue life of the considered specimens and validate the established generalized dataset for G21Mn5+N. Hence the implementation of the derived master resistance curve in numerical crack propagation calculations is featured and finally demonstrated for respective SENB-samples. This facilitates the calculation of the fatigue life of crack-affected cast steel components subjected to arbitrary load stress ratios.