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The determination of dynamic crack resistance curves from single specimen fracture tests requires information about the crack advance during the experiment. Here, attention is focused on crack resistance curves for nodular cast iron based on experimental data from instrumented Charpy tests. In order to estimate the actual crack length a key curve method (KCM) is employed. On the other hand, the Charpy impact tests were realized numerically using finite element calculations in conjunction with a continuum damage model (CDM) to simulate ductile crack growth. The parameters of the CDM model were determined from the experimental data of single specimen fracture tests. Equivalence between the experimental and the numerical realization of a fracture test was ensured by validating the predictions of the numerical simulations by means of low blow fracture tests. Comparison between the crack advance predicted by the numerical simulations and the results obtained using the proposed KCM shows a sufficiently well agreement with the actual crack length. Furthermore, crack resistance curves obtained from single specimen tests using A. Emrich · U. Michael Mühlich (B) · M. Kuna either standard estimation schemes in conjunction with the KCM or numerical simulations are compared with the predictions based on low blow fracture tests.

Abstract. Total strain-controlled low-cycle fatigue tests were performed at room temperature on a high alloyed metastable austenitic stainless cast steel in the range of 1x10 -3 ≤ Δ t/2 ≤ 3x10 -2 at constant strain rate of 4x10 -3 s -1 . The cyclic stress response revealed combinations of cyclic hardening, saturation and cyclic softening, depending on the applied cyclic total strain amplitude. Total strain amplitudes higher than 8x10-3 result in a pronounced secondary hardening up to fracture. In the case of metastable austenitic steels, at higher strain amplitudes the secondary hardening is an indicator for the austenitic-martensitic transformation. The deformation-induced α'-martensite content was detected using a nondestructive magnetic measuring technique (feritscope). The microstructure was investigated for different total strain amplitudes applying optical and scanning electron microscopy (SEM). It could be observed that with an increasing total strain amplitude the deformation band density increased considerably.

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Estimation of fatigue strength of nitrided samples by means of standardized Wohler diagramBased on results of rotation bending tests of the annealed and nitrided steel 3 1 CrMoV9 statistic verified S-N-curves were estimated.The location of the failure initiation point, surface or subsurface, has an importened influence on the parameters of the S-N-curve. The origin of failure mainly depends of the specimen geometry, the structure of the nitrided case and the load conditions. For smooth and notched specimens with subsurface failure the fatigue strength can be calculated by Kogaev and Serensen and the standardized Wohler diagram can be used for fatigue limit calculation independently of the structure of nitrided core.