TY - JOUR A1 - Schönherr, J. A. A1 - Duarte, Larissa A1 - Madia, Mauro A1 - Zerbst, Uwe A1 - Geilen, M. B. A1 - Klein, M. A1 - Oechsner, M. T1 - Robust determination of fatigue crack propagation thresholds from crack growth data JF - Materials N2 - The robust determination of the threshold against fatigue crack propagation DKth is of paramount importance in fracture mechanics based fatigue assessment procedures. The standards ASTM E647 and ISO 12108 introduce operational definitions of DKth based on the crack propagation rate da/dN and suggest linear fits of logarithmic DK– da/dN test data to calculate DKth. Since these fits typically suffer from a poor representation of the actual curvature of the crack propagation curve, a method for evaluating DKth using a nonlinear function is proposed. It is shown that the proposed method reduces the artificial conservativeness induced by the evaluation method as well as the susceptibility to scatter in test data and the influence of test data density. KW - Fatigue crack propagation threshold KW - ISO 12108 KW - ASTM E647 KW - Data evaluation methods KW - Experimental determination PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-552153 DO - https://doi.org/10.3390/ma15144737 SN - 1996-1944 VL - 15 IS - 14 SP - 1 EP - 21 PB - MDPI CY - Basel AN - OPUS4-55215 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Duarte, Larissa A1 - Madia, Mauro A1 - Zerbst, Uwe T1 - The effect of the environmental conditions on the threshold against fatigue crack propagation JF - Procedia Structutal Integrity N2 - The threshold against fatigue crack propagation (ΔKth) is a crucial parameter for the damage tolerance assessment of engineering components subjected to cyclic loading and it is composed by two distinct components, one intrinsic, dependent on the elastic material properties and the lattice type, and one extrinsic, related to the occurrence of crack closure effects. An important issue is that several factors can influence ΔKth and, in general, the fatigue crack propagation behavior. In this work, the influence of the experimental procedure, air humidity, stress ratio and test frequency on da/dN-ΔK data has been investigated. Results are discussed with their potential causes and consequences on the calculations of the residual lifetime. KW - Fatigue crack propagation threshold KW - Crack closure effect KW - Experimental procedure KW - Environmental conditions PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-544905 DO - https://doi.org/10.1016/j.prostr.2022.03.030 VL - 38 SP - 292 EP - 299 PB - Elsevier B.V. AN - OPUS4-54490 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Werner, Tiago A1 - Blasón, Sergio A1 - Madia, Mauro A1 - Kruse, Julius A1 - Benedetti, Matteo T1 - Determination of fatigue crack propagation thresholds using small-scale specimens JF - Procedia Structural Integrity N2 - The damage tolerance approach is widely used in the design and estimation of inspection intervals of safety-relevant metallic components subject to fatigue loading. The approach relies on the knowledge of the fatigue crack propagation characteristics, wherein a relevant role is played by the fatigue crack propagation threshold. Nevertheless, the use of material data determined by testing on conventional specimens is not straightforward in the case of thin-walled components such as turbine blades or additively manufactured parts, in which the local variation of material properties in highly stressed regions must be considered. In these cases, the possibility of investigating the fatigue crack propagation properties on a limited portion of material is crucial. For this purpose, a new test procedure has been developed for small-scale specimens which allows the determination of the intrinsic fatigue crack propagation threshold and the near-threshold regime. The validity and limitations of the method are demonstrated on the high strength steel S960QL, along with a comparison with data determined by testing on conventional geometries. T2 - FATIGUE DESIGN 2021 CY - Online meeting DA - 17.11.2021 KW - Fatigue crack propagation threshold KW - Small-scale specimens KW - High strength steel KW - Crack-tip constraint KW - Damage tolerance PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-544967 DO - https://doi.org/10.1016/j.prostr.2022.03.031 SN - 2452-3216 VL - 38 SP - 300 EP - 308 PB - Elsevier B.V. AN - OPUS4-54496 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Madia, Mauro A1 - Vojtek, T. A1 - Duarte, Larissa A1 - Zerbst, Uwe A1 - Pokorný, P. A1 - Jambor, M. A1 - Hutař, P. T1 - Determination of fatigue crack propagation thresholds for steel in presence of environmental effects JF - International Journal of Fatigue N2 - The experimental determination of the resistance to fatigue crack propagation in steel, particularly in the socalled near-threshold regime, is a crucial issue for safety-relevant components which are designed to operate for a large number of loading cycles before undergoing periodic inspections. This work summarizes the most relevant results of extensive experimental campaigns conducted at BAM and IPM over the last years, which have been devoted to the determination of fatigue crack propagation characteristics on medium and high strength steels. The influence of environment, oxide-induced crack closure and test methodologies in the near-threshold regime are discussed. KW - Steel KW - Fatigue crack propagation threshold KW - Oxide-induced crack closure KW - Environmental effect PY - 2021 DO - https://doi.org/10.1016/j.ijfatigue.2021.106449 SN - 0142-1123 VL - 153 SP - 1 PB - Elsevier Ltd. AN - OPUS4-53525 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Duarte, Larissa A1 - Madia, Mauro A1 - Zerbst, Uwe A1 - Schönherr, J. A. A1 - Geilen, M. B. A1 - Klein, M. A1 - Oechsner, M. T1 - Recent developments in the determination of fatigue crack propagation thresholds JF - International Journal of Fatigue N2 - The impact of crack closure and environmental effects on the experimental determination of the fatigue crack propagation threshold is a major problem for the assessment of cyclically loaded components, especially at low stress ratios 𝑅. In this work, the influence of the experimental procedure and air humidity on d𝑎∕d𝑁 − 𝛥𝐾 data at different 𝑅 is discussed. Unlike the results at 𝑅 = −1, the threshold values obtained at 𝑅 ≈ 0.8, i.e. under negligible crack closure levels, show a very small scatter band regardless of the variation of the test parameters and environmental conditions. KW - Fatigue crack propagation threshold KW - Component assessment KW - Crack closure KW - Environmental effects KW - Testing parameters PY - 2022 DO - https://doi.org/10.1016/j.ijfatigue.2022.107131 SN - 0142-1123 VL - 164 SP - 1 EP - 15 PB - Elsevier Ltd. AN - OPUS4-55403 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Zerbst, Uwe A1 - Madia, Mauro A1 - Gerwien, Peter A1 - Kucharczyk, P. A1 - Münstermann, S. A1 - Schork, B. T1 - Fracture-mechanics-based prediction of the fatigue strength of weldments. Material aspects JF - Engineering fracture mechanics N2 - Any fracture mechanics based determination of the fatigue strength of weldments requires different input information such as the local weld geometry and material data of the areas the crack is passing through during its propagation. The latter is so far not a trivial task as the fatigue crack is usually initiated at the weld toe at the transition from the weld metal to the heat affected zone and it subsequently propagates through the different microstructures of the latter to eventually grow into the base material and to cause final fracture. This paper describes how the material input information has gained particularly for heat affected zone material by thermo-mechanically simulated material specimens for two steels of quite different static strength. The data comprise the cyclic stress-strain curve, the crack closure effect-corrected crack growth characteristics, long crack fatigue crack propagation thresholds, the dependency of the parameter on the crack length and monotonic fracture resistance. The substantial experimental effort was necessary for the validation exercises of the IBESS approach, however, within the scope of practical application more easily applicable estimating methods are required. For that purpose the paper provides a number of appropriate proposals in line with its check against the reference data from the elaborate analyses. KW - Heat affected zone KW - Cyclic stress-strain curve KW - Fatigue crack propagation KW - Fatigue crack propagation threshold KW - Fracture resistance PY - 2018 DO - https://doi.org/10.1016/j.engfracmech.2017.09.010 SN - 0013-7944 SN - 1873-7315 VL - 198 SP - 79 EP - 102 PB - Elsevier AN - OPUS4-46854 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Zerbst, Uwe A1 - Madia, Mauro A1 - Maierhofer, J. A1 - Kolitsch, S. A1 - Gänser, H.-P. A1 - Pippan, R. T1 - The cyclic R-curve – Determination, problems, limitations and application JF - Engineering fracture mechanics N2 - The so-called cyclic R curve, i.e. the crack size dependence of the fatigue crack propagation threshold in the physically short crack regime, is a key parameter for bringing together fatigue strength and fracture mechanics concepts. Its adequate determination is of paramount importance. However, notwithstanding this relevance, no test guideline is available by now and only very few institutions have spent research effort on cyclic R curves so far. The aim of the present paper is to give an overview on the state-of-the-art. Besides an introduction into the basic principles, the discussion will concentrate on the experimental determination on the one hand and questions of its application on the other hand. KW - Cyclic R-curve KW - Fatigue crack propagation threshold KW - Crack closure mechanisms KW - Cyclic R-curve analysis KW - Kitagawa-Takahashi diagram PY - 2018 DO - https://doi.org/10.1016/j.engfracmech.2017.09.032 SN - 0013-7944 SN - 1873-7315 VL - 198 SP - 45 EP - 64 PB - Elsevier AN - OPUS4-46855 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -