TY - CONF A1 - Zerbst, Uwe A1 - Madia, Mauro A1 - Hildenberg, Kai A1 - Hrabe, N. T1 - Thoughts on damage tolerance and safe life design in metallic AM structures N2 - Der Vortrag bietet eine Diskussion zur Abschätzung des Schadenstoleranzverhaltens metallischer AM - Komponenten. Im Fokus stehen Probleme bei der Ermittlung repräsentativer Materialdaten, der Einfluss von Materialdefekten und Eigenspannungen. Ausgehend von derzeitigem Stand auf dem Gebiet werden Möglichkeiten der Schadenstoleranten Bauteileauslegung von AM diskutiert. N2 - The presentation provides a discussion and damage tolerant assessment of metallic AM components. In the focus are problems of the determination of representative material data, the effect of material defects and residual stresses. Starting with the actual state-of-the-art in the field, options and possibilities of a damage tolerant design for AM are discussed. T2 - BAM/NIST-Workshop on Fatigue of Additive Manufactured Metallic Components CY - Berlin, Germany DA - 16.05.2019 KW - Schadenstolerante Bauteilauslegung KW - Repräsentative Werkstoffeigenschaften KW - Defekte Eigenspannung KW - Damage tolerant component design KW - Representative material properties KW - Residual stresses PY - 2019 AN - OPUS4-48810 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Zerbst, Uwe T1 - Foreword JF - Engineering fracture mechanics N2 - The subject of this Special Issue is the fracture mechanics-based determination of the fatigue strength of weldments. Except for one, all papers were written in closer or wider relation to a methodology developed within the framework of the German Project cluster IBESS. Some of them provide background or supplementary information needed in that context but which is also relevant in a wider frame of research activities. The acronym IBESS stands for the topic of this Special Issue (in German: „Integrale Methode zu Bruchmechanischen Ermittlung der Schwingfestigkeit von Schweißverbindungen). Eight partners were involved. The cluster was cooperatively founded by the German Research Foundation (Deutsche Forschungsgemeinschaft) and by the German AiF Network (Arbeitsgemeinschaft industrieller Forschungsvereinigungen) for industrial research. KW - Fracture mechanics PY - 2018 DO - https://doi.org/10.1016/j.engfracmech.2018.05.046 SN - 0013-7944 VL - 198 IS - SI SP - 1 EP - 1 PB - Elsevier Ltd. AN - OPUS4-48696 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Zerbst, Uwe A1 - Madia, Mauro A1 - Vormwald, M. T1 - Applying fracture mechanics to fatigue strength determination - some basic considerations JF - International Journal of Fatigue N2 - A discussion is provided on demands that must be met in order to apply fracture mechanics to the determination of overall fatigue lifetime and strength, i.e., S-N curves and fatigue limits. These comprise the determination of the cyclic crack driving force for all stages of fatigue crack propagation, in particular for the short crack stage where the crack driving force has to be determined for elastic-plastic deformation and the gradual build-up of the crack closure phenomenon. Special emphasis is put on a fatigue damage relevant specification of the initial crack size. Different approaches in the literature are discussed. Another important aspect is the adequate treatment of multiple crack propagation. Finally, the discussion is illustrated by an example of a butt weld made of a medium strength steel. KW - Multiple cracks KW - Fatigue strength KW - Fracture mechanics KW - Fatigue crack propagation KW - Initial crack size PY - 2019 DO - https://doi.org/10.1016/j.ijfatigue.2019.05.009 SN - 0142-1123 VL - 126 SP - 188 EP - 201 PB - Elsevier Ltd. AN - OPUS4-48091 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Zerbst, Uwe T1 - IBESS - an integral method for fracture mechanics-based determination of the fatigue strength of weldments N2 - The paper provides an overview on the results of a German cluster project on the use of fracture mechanics to the determination of the fatigue strength of weldments with fatigue cracks originating at the weld toes. The approach includes (a) a concept for short crack propagation for which the common K concept is not applicable and the crack closure effects are still being gradually build-up, (b) a method for determining fatigue life relevant initial crack sizes as they are needed in any fracture mechanics analysis and (c) multiple cracking and crack coalescence at load levels higher than the endurance limit. The analyses are stochastically performed. Both, the endurance limit as defined for 107 loading cycles and the finite life branch of the S-N curve are determined. Besides a brief introduction into the approach, a wide range of validation examples is presented. These comprise different weldment types (butt welds, cross joints and longitudinal stiffened plates), two steels of quite different strengths, different weld geometries due to different welding techniques (TIG, MAG), as-welded and stress relieved welds and different stress ratios varying from R = -1 to R = 0.5. T2 - Vortrag beim TWI (Welding Institute) CY - Great Abington, Cambridge, UK DA - 06.06.2017 KW - Fracture mechanics KW - S-N curve KW - Weldments PY - 2017 AN - OPUS4-43771 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Zerbst, Uwe A1 - Madia, Mauro A1 - Vormwald, M. T1 - Fatigue strength and fracture mechanics JF - Procedia Structural Integrity N2 - If fracture mechanics shall be applied to the total lifetime respectively the fatigue limit of components (within the meaning of the S-N curve approach) it has to address four challenges: (a) It has to adequately describe so-called short crack propagation, which cannot be based on the common long crack concepts for principle reasons. Since the crack size is in the order of the plastic zone size, the modelling of short crack propagation cannot be based on the common linear elastic Delta K concept. Instead, an elastic-plastic parameter such as the cyclic J integral has to be applied. A second point is that the crack closure concept has to be modified in that the crack opening stress is not a constant, crack size- independent parameter but shows a transient behaviour with increasing short crack size. (b) It has to provide a meaningful definition of the initial crack dimensions as the starting point for an S-N curve relevant (residual) lifetime analysis. This can be based either on the (statistical) size of material defects which can be treated as cracks or by the size of the crack which would arrest subsequent to early crack propagation, whatever is larger. (c) It has to cope with the problem of multiple cracks for load levels higher than the fatigue limit such as it occurs in many applications in the absence of very large initial defects. (d) This requires consequent statistical treatment taking into account variations in the local geometry of the area where crack initiation has to be expected as well as the scatter in the initial crack size and in the material data used for the analyses. T2 - 2nd International Conference on Structural Integrity CY - Funchal, Madeira, Portugal DA - 04.09.2017 KW - Fatigue strength KW - Fracture mechanics KW - Initial crack size KW - Short crack propagation KW - Multiple crack propagation PY - 2017 DO - https://doi.org/10.1016/j.prostr.2017.07.065 SN - 2452-3216 VL - 5 SP - 745 EP - 752 AN - OPUS4-42545 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Zerbst, Uwe A1 - Madia, Mauro A1 - Vormwald, M. T1 - Fatigue strength and fracture mechanics N2 - If fracture mechanics shall be applied to the total lifetime respectively the fatigue limit of components (within the meaning of the S-N curve approach) it has to address four challenges: (a) It has to adequately describe so-called short crack propagation, which cannot be based on the common long crack concepts for principle reasons. Since the crack size is in the order of the plastic zone size, the modelling of short crack propagation cannot be based on the common linear elastic Delta K concept. Instead, an elastic-plastic parameter such as the cyclic J integral has to be applied. A second point is that the crack closure concept has to be modified in that the crack opening stress is not a constant, crack size- independent parameter but shows a transient behaviour with increasing short crack size. (b) It has to provide a meaningful definition of the initial crack dimensions as the starting point for an S-N curve relevant (residual) lifetime analysis. This can be based either on the (statistical) size of material defects which can be treated as cracks or by the size of the crack which would arrest subsequent to early crack propagation, whatever is larger. (c) It has to cope with the problem of multiple cracks for load levels higher than the fatigue limit such as it occurs in many applications in the absence of very large initial defects. (d) This requires consequent statistical treatment taking into account variations in the local geometry of the area where crack initiation has to be expected as well as the scatter in the initial crack size and in the material data used for the analyses. T2 - 2nd International Conference on Structural Integrity CY - Funchal, Madeira, Portugal DA - 04.09.2017 KW - Fatigue strength KW - Fracture mechanics KW - Initial crack size KW - Short crack propagation KW - Multiple crack propagation PY - 2017 AN - OPUS4-42546 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Madia, Mauro A1 - Zerbst, Uwe A1 - Beier, T. A1 - Tchoffo Ngoula, D. T1 - Approximation of the crack driving force for cracks at notches under static and cyclic loading JF - Procedia Structural Integrity N2 - The work deals with the efficient calculation of the elastic-plastic crack driving force (J-integral for monotonic loading andΔJ-integral under cyclic loading) for short cracks at notches as essential parameter for the reliable static and fatigue assessment of notched structures. The J- or ΔJ-integral is calculated based on analytical solutions for stress intensity factors, estimated by means of well-known weight function solutions in the case of cracks under power-law stress distributions. A plasticity-correction function is applied to the stress intensity factors to obtain the final expression of the crack driving force. The comparison between analytical solutions and finite element calculations in case of cracks at the weld toe in welded joints shows good agreement. T2 - 2nd International Conference on Structural Integrity CY - Funchal, Madeira, Portugal DA - 04.09.2017 KW - Structural integrity KW - Fracture mechanics KW - Crack driving force KW - Notches PY - 2017 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-425577 DO - https://doi.org/10.1016/j.prostr.2017.07.111 SN - 2452-3216 VL - 5 SP - 875 EP - 882 PB - Elsevier B.V. AN - OPUS4-42557 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Zerbst, Uwe T1 - Lessons learned on FFS particulary of (short) fatigue crack propagation N2 - The presentation provides a brief overview on results obtained in the context of fracture mechanics based flaw assessment particularly in the context of short crack propagation. Background is the planned updating of international fitness-for-service procedures such as BS 7910. Specific topics addressed are the determination of the cyclic elastic-plastic crack driving force, the description of the gradual build-up of the crack closure phenomenon at the short crack stage, cyclic R curve analysis and residual stresses. T2 - 2nd "Mind the Gap" in FFS assessment procedures workshop CY - Bristol, United Kingdom DA - 19.10.2017 KW - Reference yield load KW - Cyclic J-integral KW - Crack closure phenomenon PY - 2017 AN - OPUS4-42559 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Madia, Mauro A1 - Zerbst, Uwe A1 - Beier, T. A1 - Schork, B. T1 - The IBESS model – Elements, realisation and validation JF - Engineering fracture mechanics N2 - The work presents the procedure developed within the German research project IBESS, which allows for the fracture mechanics-based prediction of the fatigue strength of welded joints under constant amplitude loading. Based on the experimental observations of the crucial failure mechanisms, the approach focuses on the short crack propagation, where elastic-plastic fracture mechanics and the build-up of closure effects must be considered as well as the variability of the local geometry at the weld toe and the modelling of multiple crack interaction. Analytical solutions are provided for the approximation of the through-thickness stress profiles at the weld toe and for the determination of the crack driving force in the form of a plasticity-corrected stress intensity factor range ∆K_p. Proposals for the determination of the initial crack size and the crack closure factor are also included. The approach is validated against a large number of experimental data, which comprises fatigue tests on individual cracks monitored by heat tinting and beach-marking techniques, as well as stress life curves. Three kinds of welded joints, two steels of significant different strengths and three stress ratios are considered. The results show that the procedure provides good estimations of the statistical distribution of the fatigue strength of welded joints both for the finite and infinite life regime. Furthermore, the predictions are compared with available benchmark data for structural steels. KW - Welded joints KW - Life prediction KW - Fatigue crack growth KW - Short cracks KW - Crack closure PY - 2018 DO - https://doi.org/10.1016/j.engfracmech.2017.08.033 SN - 0013-7944 SN - 1873-7315 VL - 198 SP - 171 EP - 208 PB - Elsevier AN - OPUS4-46852 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 -