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- Zeitschriftenartikel (57) (entfernen)
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- Fracture mechanics (15)
- Fatigue strength (11)
- Fatigue crack propagation (7)
- Fatigue crack propagation threshold (7)
- Weldments (6)
- Cyclic R-curve (5)
- Fatigue (5)
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- Railway axles (4)
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- Flaw assessment (3)
- Kitagawa-Takahashi diagram (3)
- Non-metallic inclusions (3)
- R6 procedure (3)
- Additive manufacturing (2)
- Component assessment (2)
- Constraint (2)
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- Endurance limit (2)
- Experimental determination (2)
- FITNET (2)
- Fatigue crack growth (2)
- Fracture (2)
- Fracture resistance (2)
- Fracture toughness (2)
- Multiple cracks (2)
- Pores (2)
- R6 (2)
- Railway rails (2)
- Residual stresses (2)
- S-N curve (2)
- SINTAP (2)
- Safe life design (2)
- Strength mismatch (2)
- Weld toe geometry (2)
- Welded joints (2)
- Welding residual stresses (2)
- 316L (1)
- AM 316L stainless steel (1)
- ASTM E647 (1)
- Accompanying measures (1)
- Additive Manufacturing (1)
- BS 7910 (1)
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- Crack closure mechanisms (1)
- Critical distance (1)
- Cyclic J-integral (1)
- Cyclic R-curve analysis (1)
- Cyclic stress-strain curve (1)
- Damage tolerance design (1)
- Data evaluation methods (1)
- Elastic follow-up (1)
- Elastic-plastic fracture mechanics (1)
- Environment (1)
- Environmental conditions (1)
- Environmental effect (1)
- Environmental effects (1)
- Experimental procedure (1)
- FAT class (1)
- FAT class approach (1)
- FAT class concept (1)
- Fail-safe design (1)
- Failure analysis (1)
- Failure probability (1)
- Fatigue crack (1)
- Fatigue crack initiation (1)
- Fatigue crack propagation stages (1)
- Fatigue life (1)
- Fatigue life prediction (1)
- Fatigue loading (1)
- Fatigue strength and life (1)
- Finite element (FE) (1)
- Flaw assessment procedures (1)
- Flaw interaction (1)
- Flying ballast impact (1)
- Foot crack (1)
- Fracture assessment (1)
- Global stability criterion (1)
- Graphite modules (1)
- HCF (1)
- Heat affected zone (1)
- IBESS (1)
- ISO 12108 (1)
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- In-situ Process Monitoring (1)
- Inclusion cluster (1)
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- Inclusions (1)
- Influencing factors (1)
- Initial flaw size (1)
- Inspection intervals (1)
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- L-PBF (1)
- LCF (1)
- Life prediction (1)
- L‐PBF (1)
- Material defects (1)
- Material inhomogeneity (1)
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- Mis-match (1)
- Monotonic and cyclic crack driving force (1)
- Multiple crack initiation (1)
- Multiple cracking (1)
- Nichtmetallische Einschlüsse (1)
- Non-destructive Materials (1)
- Non-destructive testing (1)
- Non-propagating cracks (1)
- Non-sharp defects (1)
- Notch fatigue (1)
- Notch sensitivity (1)
- Notches (1)
- Nuclear reactor systems (1)
- Oxide-induced crack closure (1)
- Peak stress method (PSM) (1)
- Pipes (1)
- Plastic collapse (1)
- Process development (1)
- R-curve analysis (1)
- Radsatzwellen (1)
- Railway axle (1)
- Reference stress method (1)
- Residual lifetime (1)
- Root cause (1)
- Safety (1)
- Schadenstoleranz (1)
- Schwingfestigkeit (1)
- Scratches (1)
- Secondary stresses (1)
- Short fatigue-cracks (1)
- Shrinkages (1)
- Sichere Lebensdauer (1)
- Standardisation (1)
- Statistics (1)
- Steel (1)
- Steinschlag (1)
- Stiffness (1)
- Strength mis-match (1)
- Stress analysis (1)
- Stress intensity factor (1)
- Structural integrity (1)
- Structures (1)
- Surface roughness (1)
- SN curve (1)
- Tearing instability (1)
- Testing parameters (1)
- Transferability to components (1)
- Turbine disk (1)
- Weld fatigue (1)
- Weld geometry (1)
- Weld toes (1)
- Zerstörungsfreie Inspektion (1)
Organisationseinheit der BAM
- 9 Komponentensicherheit (31)
- 9.4 Integrität von Schweißverbindungen (30)
- 5 Werkstofftechnik (5)
- 5.1 Mikrostruktur Design und Degradation (4)
- 9.0 Abteilungsleitung und andere (4)
- 9.6 Additive Fertigung metallischer Komponenten (4)
- 8 Zerstörungsfreie Prüfung (3)
- 8.5 Röntgenbildgebung (3)
- 4 Material und Umwelt (2)
- 4.0 Abteilungsleitung und andere (1)
Paper des Monats
- ja (1)
An analytical fracture mechanics model for predicting the finite life fatigue strength of components is
presented which combines a number of well established and newly developed approaches such as
Murakami's and McEvily's approach for describing the transient behaviour of crack closure of short
cracks, the analytical (long) crack closure function of Newman which became part of the widely used
NASGRO approach, the R6 procedure, a method for improving the ligament yielding correction f(Lr ) of
R6 proposed by the authors of the present paper and other elements. Basic assumption is the preexistence
of initial flaws such that the crack initiation or nucleation stage is small and can be neglected.
The application of the model is demonstrated for small tension plates of aluminium Al 5380 H321 with
artificial initial defects generated by FIB technology, the size of which was fixed on the basis of
fractographic investigations on broken, smooth specimens.
The paper gives an overview on safe life and damage tolerance methods applied to railway axles. It describes failure scenarios due to fatigue crack initiation and propagation. Besides common aspects of design, specific features such as corrosion and impact damage from flying ballast are discussed which may reduce the fatigue strength of axles during service. Potential effects of non-metallic inclusions from the steel manufacturing process are addressed in the context of the very high number of loading cycles railway axles are designed for. With respect to damage tolerance general lines of fracture mechanics residual lifetime analyses are introduced. More specific discussion is provided on aspects such as the threshold value of fatigue crack propagation and reliability aspects of non-destructive inspection.
The net section limit load FY necessary for assessment at static loading is a key input for the accuracy of any elasticplastic flaw assessment procedure of the R6 type. Unfortunately available limit load solutions are of variable quality since they have been obtained over decades by different methods. As a consequence the results of the fracture analyses such as the critical load or crack size are limited in their accuracy and are often significantly conservative. Further, common limit load solutions based on ligament yielding are inadequate in a number of cases even for through crack configurations and should be replaced by some kind of local yielding solutions. In the present paper a simple and straightforward reference load definition is proposed instead of the limit load which strictly corresponds to a ligament yielding parameter Lr = 1 in the R6 Routine and similar approaches such as the European SINTAP and FITNET methods. This can be determined by finite element simulation for any geometry. In addition to a previous study on thin wall notched plates the method is applied to plates containing shallow semi-elliptical surface cracks. The results demonstrate that the approach provides a suitable extension and improvement of the existing methods.
The safety assessment of railway axles is based on a two-stage approach: fatigue strength design and regular inspections which, in terms of a general safety philosophy refer to safe-life and damage tolerance concepts. Starting with a recent failure case, a broken axle of a German high speed train, a discussion is presented on issues of both safety levels. These include ideas for finite life design, the treatment of in-service effects on the fatigue strength due to flying ballast damage and corrosion pits, the effect of corrosion on fatigue crack initiation and propagation, potential effects of non-metallic inclusions in steels, the way to detect them by quality control measures and reliability aspects of non-destructive testing with respect to the detection of fatigue cracks. Proposals are made how the safety level could be further improved.
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.
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.
The effect of the environmental conditions on the threshold against fatigue crack propagation
(2022)
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.
The Kitagawa-Takahashi (KT) diagram is a proven concept for describing the fatigue limit in presence of a defect or crack. It can be determined empirically with great experimental effort. It can also be estimated by means of the El Haddad relationship if the endurance limit and the long fatigue crack propagation threshold are available in reasonable accuracy. A third option is the determination using the cyclic R-curve, which describes the dependency of the fatigue crack propagation threshold on the crack growth at the short crack propagation stage. This can be experimentally determined using a closure-free initial pre-crack. It can then be applied to the determination of crack arrest for a given applied load and a given defect or crack size. Compared to the other two methods mentioned above, this option has considerable advantages: It can be applied to any component and any stress ratio. It allows the treatment of multiple cracks and provides estimations of the S-N curve in the finite life regime as well as at the endurance limit. Compared to the empirical determination of the KT diagram, the experimental effort is significantly lower and compared to the El Haddad approach it avoids problems such as the use of non-conservative long fatigue crack propagation thresholds (when the conventional load reduction method is applied to materials prone to corrosion) and the mathematical predetermination of the curve shape. The work introduces the method and provides a critical discussion as well as quantitative comparison between the different methods.
Additive manufacturing (AM) is becoming increasingly important in engineering applications due to the possibility of producing components with a high geometrical complexity allowing for optimized forms with respect to the in-service functionality. Despite the promising potential, AM components are still far from being used in safety-relevant applications, mainly due to a lack of understanding of the feedstock-process-properties-performance relationship. This work aims at providing a full characterization of the fatigue behavior of the additively manufactured AISI 316L austenitic stainless steel and a direct comparison with the fatigue performance of the wrought steel. To this purpose, a set of specimens has been produced by laser powder bed fusion (L-PBF) and subsequently heat treated at 900 °C for 1 hour for complete stress relief, whereas a second set of specimens has been machined out of hot-rolled plates. Low cycle fatigue (LCF) and high cycle fatigue (HCF) tests have been conducted for characterizing the fatigue behavior. The L-PBF material had a higher fatigue limit and better finite life performance compared to wrought material. Both, LCF and HCF-testing revealed an extensive cyclic softening.
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.