Filtern
Erscheinungsjahr
Dokumenttyp
- Beitrag zu einem Tagungsband (18)
- Vortrag (15)
- Zeitschriftenartikel (6)
- Buchkapitel (1)
- Beitrag zu einem Sammelband (1)
- Dissertation (1)
- Sonstiges (1)
Schlagworte
- Fatigue (17)
- Concrete (10)
- Ermüdung (6)
- Beton (5)
- Damage evolution (5)
- Gründungsstrukturen (4)
- High-cycle (4)
- Crack detection (3)
- Damage Evolution (3)
- High-Cycle (3)
- Leichtbau (3)
- Offshore (3)
- Offshore Windenergieanlagen (3)
- Steel structures (3)
- Ultrasonic testing (3)
- Automatisierte schweißtechnische Fertigung (2)
- Coupler systems (2)
- Cracks (2)
- Grouted connection (2)
- High-speed (2)
- High-strength concrete (2)
- Reinforcement (2)
- Schädigung (2)
- Acoustic emission (1)
- Acoustic emission analysis (1)
- Acoustic emission testing (1)
- Automatisierte Fertigung (1)
- Automatisierte schweißtechniche Fertigung (1)
- Ballast (1)
- Bemessung (1)
- Bionik (1)
- Bruchlastwechselzahlen (1)
- Compression (1)
- Compressive Cyclic loading (1)
- Compressive cyclic loading (1)
- Concrete sleepers (1)
- Constitutive modeling (1)
- Crack (1)
- Crack formation (1)
- Crack growth (1)
- Crack pattern (1)
- Cyclic load (1)
- Cyclic loading (1)
- Damage (1)
- Degradation (1)
- Detection (1)
- Digital image correlation (1)
- Druckfestigkeit (1)
- Druckschwellenversuch (1)
- Energy (1)
- Ermüdungsverhalten (1)
- Failure (1)
- Fatigue damage (1)
- Fatigue strength (1)
- Feuchte (1)
- Grouted Connection (1)
- Grouted connections (1)
- Hochfester Beton (1)
- Hochzyklisch (1)
- Impact (1)
- Imperfektion (1)
- Joint capacity (1)
- Large components (1)
- Lehm (1)
- Leichtbauprinzipien (1)
- Local approaches (1)
- Luminescence (1)
- Mauerwerk (1)
- NDT (1)
- Non destructive testing (1)
- Non-destructive testing (1)
- Normal strength concrete (1)
- Offshore Windenergie (1)
- Offshore wind energy (1)
- Probekörpergeometrien (1)
- Probengeometrie (1)
- Probengröße (1)
- Rehabilitation (1)
- Repair (1)
- Schallemission (1)
- Schrauben (1)
- Schädigungsevolution (1)
- Shear keys (1)
- Shell Buckling (1)
- Size effect (1)
- Slenderness effect (1)
- Soil-Structure-Interaction (1)
- Static load (1)
- Strengthening strategy (1)
- Tensile test (1)
- Test specification (1)
- Track assessment (1)
- Track optimisation (1)
- Train-track-modelling (1)
- Transverse butt weld (1)
- Vorspannung (1)
- Weld imperfections (1)
- Welded (1)
- Wind (1)
- Wind Energy (1)
- Wind energy (1)
- Wind turbine tower (1)
- Windenergieanlage (1)
Organisationseinheit der BAM
- 7 Bauwerkssicherheit (23)
- 7.2 Ingenieurbau (22)
- 7.1 Baustoffe (6)
- 7.0 Abteilungsleitung und andere (5)
- 9 Komponentensicherheit (4)
- 9.3 Schweißtechnische Fertigungsverfahren (4)
- 7.4 Baustofftechnologie (2)
- 8 Zerstörungsfreie Prüfung (1)
- 8.3 Thermografische Verfahren (1)
- 8.4 Akustische und elektromagnetische Verfahren (1)
Paper des Monats
- ja (1)
Eingeladener Vortrag
- nein (15)
Unter zyklischen Belastungen findet im Beton, wie bei anderen Materialien auch, ein Ermüdungsprozess statt, der letztlich im Versagen des Materials enden kann. Im derzeitigen Erkenntnisstand zum Materialverhalten des Betons gibt es gerade bei dessen Ermüdungsverhalten noch viele nicht oder nicht ausreichend geklärte Fragestellungen. Deshalb wurde in Laborversuchen das Ermüdungsverhalten von Beton unter Druckschwellbeanspruchungen untersucht. Im Fokus dieser Untersuchungen standen dabei die während der Lebensdauer im Materialgefüge ablaufenden Prozesse, die zur Schädigung des Gefüges und schließlich auch zum Ermüdungsversagen führen können.
In den Ermüdungsversuchen wurden versuchsbegleitend Dehnungsmessungen, Ultraschall-Laufzeitmessungen und Schallemissionsmessungen an den Proben zur Erfassung der Schädigungsevolution eingesetzt. Die Schallemissionsmessung ist dabei ein wichtiges Instrument, da sie die Rissentwicklungsprozesse detektiert, die die Ursache für die Materialschädigung sind. Mit ihr konnten die unterschiedlichen Phasen der Rissentwicklungen über die gesamte Lebensdauer der Betonproben festgestellt werden. Diese Phasen sind gekennzeichnet durch sich stabilisierende, stabile und instabile Rissprozesse, die entsprechende Auswirkungen auf das Materialverhalten haben. Ein Vergleich mit den Ergebnissen der anderen Messtechniken zeigt den entsprechenden Einfluss der Rissentwicklungen auf die Materialeigenschaften des Betons.
The fatigue process of concrete under compressive cyclic loading is still not completely explored. The corresponding damage processes within the material structure are especially not entirely investigated. The application of acoustic measurement methods enables a better insight into the processes of the fatigue in concrete. Normal strength concrete was investigated under compressive cyclic loading with regard to the fatigue process by using acoustic methods in combination with other nondestructive measurement methods. Acoustic emission and ultrasonic signal measurements were applied together with measurements of strains, elastic modulus, and static strength. It was possible to determine the anisotropic character of the fatigue damage caused by uniaxial loading based on the ultrasonic measurements. Furthermore, it was observed that the fatigue damage seems to consist not exclusively of load parallel oriented crack structures. Rather, crack structures perpendicular to the load as well as local compacting are likely components of the fatigue damage. Additionally, the ultrasonic velocity appears to be a good indicator for fatigue damage beside the elastic modulus. It can be concluded that acoustic methods allow an observation of the fatigue process in concrete and a better understanding, especially in combination with further measurement methods.
Fatigue is of relevance not only for metals but also for concrete. The current knowledge about fatigue behaviour of concrete is, however, incomplete. This concerns especially the progress of fatigue which precedes the fatigue failure. Some macroscopic effects of this process are well known but the governing material changes behind them are still less studied. The focus of the present contribution lay on a systematic and comprehensive investigation of the fatigue process under cyclic compressive loading. The aim was to obtain a deeper insight and to provide a better understanding of the damage process in the material. Cylindrical specimens were tested with a number of cycles to failure between 106 and 107. Various methods of non-destructive and destructive testing were used to investigate macroscopic and microscopic changes in the material. One main result was that the changes in the macroscopic material behaviour could not be explained only by the development of micro cracks. The results indicated that the related changes in the fatigue behaviour originate rather from viscous processes in the cement stone, similar to the process of creep. A sound description of the possible processes was derived from the obtained experimental results which concerns material structure during fatigue loading. It has been shown that in case of isotropic material behaviour a stiffness reduction related to a scalar value could not capture the damage effect on the stress-strain relationship caused by fatigue.
The current knowledge about fatigue behavior of concrete is still incomplete. This concerns especially the progress of fatigue which precedes the fatigue failure. Therefore, the process of fatigue itself under cyclic compressive loading was investigated in a systematic and comprehensive way. The aim of this investigation was to obtain a deeper insight and to provide a better understanding of the damage process occurring within the material during fatigue loading. Concrete cylinders were tested with a number of cycles to failure between 106 and 107. To investigate macroscopic and microscopic changes in the material, various methods of non-destructive and destructive testing were used. One main result was, in contrast to other authors, that the investigated changes in macroscopic material behavior could not be explained only by a development of micro-cracks. The results indicated rather, that the related changes in the fatigue behavior are mainly a result of viscous processes in the hardened cement paste, similar to the processes of creep. Based on the experimental results a description of the possible processes was derived which take place in the material structure during fatigue loading and also leads to the observed macroscopic changes in the material behavior. In this context, the results have shown that in case of isotropic material behavior a stiffness reduction related to a scalar value could not capture the damage effect on the stress-strain-relationship caused by fatigue.
The current knowledge about fatigue behavior of concrete is still incomplete. This concerns especially the progress of fatigue which precedes the fatigue failure. Therefore, the process of fatigue itself under cyclic compressive loading was investigated in a systematic and comprehensive way. The aim of this investigation was to obtain a deeper insight and to provide a better understanding of the damage process occurring within the material during fatigue loading. Concrete cylinders were tested with a number of cycles to failure between 106 and 107. To investigate macroscopic and microscopic changes in the material, various methods of non-destructive and destructive testing were used. One main result was, in contrast to other authors, that the investigated changes in macroscopic material behavior could not be explained only by a development of micro-cracks. The results indicated rather, that the related changes in the fatigue behavior are mainly a result of viscous processes in the hardened cement paste, similar to the processes of creep. Based on the experimental results a description of the possible processes was derived which take place in the material structure during fatigue loading and also leads to the observed macroscopic changes in the material behavior. In this context, the results have shown that in case of isotropic material behavior a stiffness reduction related to a scalar value could not capture the damage effect on the stress-strain-relationship caused by fatigue.
Reinforced concrete is a widely used material for power generation structures, where load scenarios like impact loadings need to be considered. In this context mechanical splicing systems for the connection of reinforcement bars are of specific interest and impact resistance for the splicing systems has to be verified. High speed tensile tests need to be performed on splicing systems for reinforcement bars to confirm the capability of the coupler to resist impact loading. Furthermore, the ability of the reinforcement steel to dissipate energy by ductile behaviour with pronounced plastic strains should be confirmed by these tests. During the last decades comprehensive experiences were developed at BAM performing high speed tensile tests on reinforcement bars as well as on several splicing systems. For the lack of available standards defining these tests in detail an appropriate test procedure was developed and continuously optimized during this period at BAM. The test procedure is partially based on testing principles adapted from available standards. The main intention behind this test procedure is to perform high-speed tensile tests with a specific constant strain rate generated at the specimen. Furthermore, main objective was to establish a procedure to guarantee the comparability of test results for different diameter of reinforcement as well as for different types of couplers. Besides the pure execution of the high-speed tensile tests, the test specification also declares how to evaluate the measurements and the test results. Finally, some typical results will be presented in this contribution.
This document presents the specification for the execution and evaluation of high-speed tensile tests on reinforcement bar coupler systems. This specification was developed at BAM - Bundesanstalt für Materialforschung und -prüfung (Federal Institute for Materials Research and Testing, Germany) - following test principles from related international standards.
The present document represents the latest status of the test specification. It is noted that until 2010 the test procedure was characterised on a test velocity based on L0. In an improved test conception and after intensive investigations in cooperation with industry partners, this procedure has been updated to consider instead a test velocity based on Lr, since this warrants more comparable and meaningful results.
At present, to produce renewable energy offshore wind farms play an important role. The available space combined with the more valuable wind conditions make offshore locations very attractive for wind powered energy production. In Europe a significant number of offshore wind farms already exist, especially in the North and Baltic Sea. In future this trend will continue, and further offshore wind farms will be built. The majority of offshore wind turbines are mounted on steel foundation structures. Due to the high-cyclic loading by wind and waves fatigue stress plays a substantial role regarding structural safety.
Besides the consideration of fatigue within the design process, to monitor existing steel structures for potential fatigue cracks during their life time is a major topic and a challenge.
For the structures of the offshore wind turbines are large and partially under water effective reliable methods for the detection of fatigue cracks are required.
This contribution presents investigations on different crack detection methods applied at high-cycle fatigue tests on small-scale welded steel samples as well as on large-scale welded steel components. The tests were conducted at the BAM laboratories. For crack detection mainly three different methods were used and compared. The first method regards to the measurement of strain by conventionally strain gauges. Secondly, the crack luminescence was used as a new and effective optical method for surface monitoring. And finally, crack detection by pressure differentials of the inner and outer section of tubular steel elements was investigated. A comparison study will emphasize the advantages and disadvantages of the different methods and show which of the described methods is potentially more suitable for an application on real offshore wind structures.
Unter zyklischen Belastungen findet im Beton, wie bei anderen Materialien auch, ein Ermüdungsprozess statt. Im derzeitigen Erkenntnisstand zum Materialverhalten des heterogenen Betons gibt es gerade bei dessen Ermüdungsverhalten momentan noch viele nicht oder nicht ausreichend geklärte Fragestellungen. Deshalb befasst sich der vorliegende Beitrag mit der experimentellen Untersuchung des Ermüdungsverhaltens von Beton, speziell unter hochzyklischen Druckschwellbelastungen. Im Fokus der Untersuchungen stehen dabei die während der gesamten Lebensdauer im Materialgefüge ablaufenden Prozesse, die zu Veränderungen im Materialverhalten und schließlich auch bis zum Ermüdungsversagen führen können. Ziel ist es, eine möglichst realitätsnahe Beschreibung des im Materialgefüge ablaufenden Ermüdungsprozesses zu entwickeln.