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 - Scacco, F. A1 - Zerbst, Uwe A1 - Meneghetti, G. A1 - Madia, Mauro T1 - Comparison between PSM and IBESS approaches for the fatigue life estimation of weldments JF - Welding in the World N2 - In the framework of the fatigue assessment of welded components, several methods are available in design standards such as the nominal stress, hot-spot stress, notch stress and linear elastic fracture mechanics approaches. The present paper aims at comparing two advanced local approaches for the fatigue strength assessment of different welded joints made of steel. The first one is IBESS which is based on short crack fracture mechanics. The second one is the PSM which instead involves the strain energy density approach. Both methods will be briefly presented, and the fatigue life prediction results discussed. The results obtained for the joint geometries considered in this work show advantages and drawbacks of the approaches, which are thoroughly analysed as well. KW - Fatigue KW - Welded joints KW - FAT class KW - IBESS KW - Peak stress method (PSM) KW - Finite element (FE) PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-545139 DO - https://doi.org/10.1007/s40194-022-01284-7 SP - 1 EP - 23 PB - Springer AN - OPUS4-54513 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schork, B. A1 - Zerbst, Uwe A1 - Kiyak, Yusuf A1 - Kaffenberger, M. A1 - Madia, Mauro A1 - Oechsner, M. T1 - Effect of the parameters of weld toe geometry on the FAT class as obtained by means of fracture mechanics-based simulations JF - Welding in the World N2 - The fracture mechanics-based IBESS approach is applied to the determination of FAT classes of butt welds with crack Initiation along the weld toe. The aim is an investigation of the effect of the geometrical parameters toe radius, flank angle, reinforcement and secondary notches such as roughness or undercuts. The influence of these parameters is discussed both individually and in combination; however, excluding statistical distributions of them and the material data. The results, when compared with conventional FAT classes for butt welds, are encouraging with respect to a potential contribution of IBESS to the discussion of more advanced quality criteria for welds. To that purpose, demands for further research are proposed. KW - Fracture mechanics KW - Weld toe geometry KW - Fatigue crack initiation KW - FAT class approach PY - 2020 DO - https://doi.org/10.1007/s40194-020-00874-7 IS - 64 SP - 925 EP - 936 PB - Springer AN - OPUS4-53079 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bergant, M. A1 - Werner, Tiago A1 - Madia, Mauro A1 - Yawny, A. A1 - Zerbst, Uwe T1 - Short crack propagation analysis and fatigue strength assessment of additively manufactured materials: An application to AISI 316L JF - International Journal of Fatigue N2 - This paper presents the application of short crack propagation models based on the cyclic R-curve for assessing the fatigue strength of additively manufactured (AM) materials containing fabrication defects. Chapetti’s and IBESS models were implemented in combination with Murakami’s √area parameter, considering recently published data on laser powder bed fusion processed AISI 316L stainless steels. Estimated S-N curves and Kitagawa-Takahashi diagrams predict fairly well the experimental data, especially the origin of the failure from internal or surface defects. These results provide an indication that the methods based on the cyclic R-curve constitute suitable tools for fatigue behavior assessment of AM materials. KW - AM 316L stainless steel KW - Cyclic R-curve KW - Chapetti’s and IBESS model KW - S-N curve KW - Kitagawa-Takahashi diagram PY - 2021 DO - https://doi.org/10.1016/j.ijfatigue.2021.106396 VL - 151 PB - Elsevier Ltd. AN - OPUS4-53082 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 - Zerbst, Uwe A1 - Madia, Mauro A1 - Bruno, Giovanni A1 - Hilgenberg, Kai T1 - Towards a Methodology for Component Design of Metallic AM Parts Subjected to Cyclic Loading JF - Metals N2 - The safe fatigue design of metallic components fabricated by additive manufacturing (AM) is still a largely unsolved problem. This is primarily due to (a) a significant inhomogeneity of the material properties across the component; (b) defects such as porosity and lack of fusion as well as pronounced surface roughness of the asuilt components; and (c) residual stresses, which are very often present in the as‐built parts and need to be removed by post‐fabrication treatments. Such morphological and microstructural features are very different than in conventionally manufactured parts and play a much bigger role in determining the fatigue life. The above problems require specific solutions with respect to the identification of the critical (failure) sites in AM fabricated components. Moreover, the generation of representative test specimens characterized by similar temperature cycles needs to be guaranteed if one wants to reproducibly identify the critical sites and establish fatigue assessment methods taking into account the effect of defects on crack initiation and early propagation. The latter requires fracture mechanics‐based approaches which, unlike common methodologies, cover the specific characteristics of so‐called short fatigue cracks. This paper provides a discussion of all these aspects with special focus on components manufactured by laser powder bed fusion (L‐PBF). It shows how to adapt existing solutions, identifies fields where there are still gaps, and discusses proposals for potential improvement of the damage tolerance design of L‐PBF components KW - L‐PBF KW - Fatigue KW - Fracture KW - Defects PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-525822 DO - https://doi.org/10.3390/met11050709 VL - 11 IS - 5 SP - 709 PB - MDPI CY - Basel AN - OPUS4-52582 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Zerbst, Uwe A1 - Madia, Mauro A1 - Kiyak, Yusuf A1 - Breidung, Marc A1 - Baer, Wolfram A1 - Küppers, M. ED - Madia, Mauro T1 - Stiffness/constraint effects in analytical flaw assessment - A technical note JF - Engineering Fracture Mechanics N2 - Using the case study of a fail-safe design criterion for a steering knuckle of a commercial vehicle, the effect of stiffness/constraint on the crack driving force in the component is discussed. The problem arises when assessment procedures such as R6, BS 7910 or SINTAP/FITNET are applied in conjunction with substitute geometries for determining the model parameters K-factor and limit load (or a substitute for the latter), as it is common practice. In the example, the conservatism was so pronounced that this procedure was in fact unusable. A way out could be the finite element-based determination of the model parameters and their use in the analytical framework. This procedure is useful and effective if the finite element-based calculations are used in parameter sensitivity analyses. KW - Fail-safe design KW - Fracture resistance KW - Fracture assessment KW - Stiffness KW - Constraint PY - 2022 DO - https://doi.org/10.1016/j.engfracmech.2022.108728 SN - 0013-7944 IS - 273 SP - 1 EP - 15 PB - Elsevier Science CY - Kidlington AN - OPUS4-55544 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 T1 - Analytical flaw assessment JF - Engineering Fracture Mechanics N2 - The paper provides a review on analytical flaw assessment methods with the focus on fracture under monotonic loading and fatigue crack propagation. The first topic comprises linear elastic as well as elastic-plastic fracture mechanics approaches. It essentially follows their historical development. Topics which are separately discussed are reference/Limit loads, the treatment of secondary stresses, strength mismatch, constraint, unstable crack propagation (monotonic R-curve analyses) and statistical aspects. With respect to fatigue crack propagation the analytical treatment of crack closure and constraint and the Determination of the cyclic elastic-plastic crack driving force is discussed. Finally, cyclic Rcurve analyses are briefly addressed. KW - Monotonic and cyclic crack driving force KW - Secondary stresses KW - Strength mismatch KW - Constraint KW - Crack closure KW - R-curve analysis PY - 2018 DO - https://doi.org/10.1016/j.engfracmech.2017.12.002 SN - 0013-7944 SN - 1873-7315 VL - 187 SP - 316 EP - 367 PB - Elsevier AN - OPUS4-44234 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Zerbst, Uwe A1 - Klinger, Christian T1 - Material defects as cause for the fatigue failure of metallic components JF - International Journal of Fatigue N2 - The paper provides an overview on material defects which may serve as fatigue crack initiation sites and can cause final fatigue failure of a component. These comprise nonmetallic inclusions in Steel and aluminum alloys, cavities such as pores, micro-shrinkages and un-welded regions in cast, sinter and additively manufactured alloys, graphite nodules, shrinkages and other items in modular cast iron, regions of defective microstructure, microcracks and secondary notches such as undercuts and surface roughness. Besides their origin, the effect and mechanisms on fatigue crack initiation and propagation are discussed. The considerations are proceeded and accompanied by a Brief discussion of some Basic aspects such as the stages of crack propagation along their length scale, the overcoming of crack arrest and the question when a secondary notch can be treated as a crack. KW - Material defects KW - Fatigue strength and life KW - Non-metallic inclusions KW - Pores KW - Shrinkages KW - Graphite modules KW - Surface roughness PY - 2019 DO - https://doi.org/10.1016/j.ijfatigue.2019.06.024 SN - 0142-1123 SN - 1879-3452 VL - 127 SP - 312 EP - 323 PB - Elsevier AN - OPUS4-49127 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -