Filtern
Dokumenttyp
- Vortrag (25) (entfernen)
Sprache
- Englisch (25)
Referierte Publikation
- nein (25) (entfernen)
Schlagworte
- Steel (25) (entfernen)
Organisationseinheit der BAM
- 7 Bauwerkssicherheit (11)
- 7.6 Korrosion und Korrosionsschutz (7)
- 9 Komponentensicherheit (5)
- 7.3 Brandingenieurwesen (4)
- 9.4 Integrität von Schweißverbindungen (4)
- 1 Analytische Chemie; Referenzmaterialien (2)
- 1.6 Anorganische Referenzmaterialien (2)
- 7.5 Technische Eigenschaften von Polymerwerkstoffen (2)
- 9.0 Abteilungsleitung und andere (2)
- 5 Werkstofftechnik (1)
Eingeladener Vortrag
- nein (25)
The detection and characterization of surface breaking cracks in steel prior to damage is a technologically as well as economically important task especially for safety-relevant structures. Detection of small cracks already during the steel production process might significantly reduce the risk of failure and reduce production costs due to an obsolete post-processing.
However, the hostile environmental conditions (high temperature specimens) together with very strict requirements in current steel production (production speeds, in-line testing and evaluation) are challenging and render many well-established NDE techniques hardly applicable.
We present an approach to use laser thermographic testing as a fast, remote and contactless NDE method, that addresses these challenges and might ultimately allow for online crack detection.
The basic idea of laser thermographic testing, introduced by Kubiak in 1968, is the monitoring of the heat flow as induced by local heating. Disturbances within the heat flow generated by the presence of surface cracks can then be analyzed by image processing algorithms, as we have shown in previous work.
The aim of the presented work is to advance laser thermographic testing to be applicable to the specific conditions of steel production environments. This purpose was met by the development of a laboratory setup that allows us to simulate production conditions, as rolling speed, specimen temperature, laser heating power and study their influence on crack detection performance. This parametric study enabled us to develop and improve data processing and crack detection algorithms with the final goal of providing optimized in-line crack detection. The studies were accompanied by comprehensive FEM simulations to intensify the understanding of the contrast formation as well as the crucial parameters influencing the performance of the method.
The wetting behavior of material surfaces can be controlled by surface structures. We functionalized case-hardened alloyed carbon steel to modify the wetting behavior using ultrashort laser pulses (fs- to ps-range). The laser processing was performed by scanning the laser beam across the surface of initially polished flat sample material. An experimental study of the laser processing parameters (peak fluence, scan velocity, line overlap) rendered an assignment of different regimes associated with characteristic surface morphologies (laser-induced periodic surface structures, grooves, micro cones, etc.) possible. Analyzing the surface using optical as well as scanning electron microscopy allowed the identification of morphologies providing the optimum similarity to the natural skin of non-moisture havesting lizards. For mimicking skin structures of moisture-harvesting lizards, additionally a two-step laser processing strategy was established for realizing hierarchical microstructures. In this approach, micrometer-scaled capillaries (step 1) were superimposed by a laser-generated regular array of small dimples (step 2). Optical focus variation imaging measurements finally revealed the three dimensional topography of the laser processed surfaces derived from lizard skin structures. The functionality of these surfaces was analyzed in view of wetting and directional fluid transport properties. The results suggest possible applications of the laser-structured surfaces.
Nature provides countless examples of surface structures featuring extraordinary properties such as directional fluid transport. In order to mimic the morphology and outstanding wetting behaviour of bark bugs, ultrashort laser pulses with durations in the fs- to ps-range were employed for large area surface processing of steel. By scanning the laser beam across the surface of initially polished flat sample surfaces and systematically varying the laser processing parameters (peak fluence, scan velocity, line overlap), different regimes associated with characteristic surface morphologies (laser-induced periodic surface structures (LIPSS), grooves, spikes, etc.) could be identified. Additionally, different laser processing strategies were applied, varying laser wavelength, pulse duration and repetition rates, which allowed to achieve a range of morphologies that resemble different structures found on bark bugs. For identifying the ideal combination of parameters for mimicking such bug-like structures, the surfaces were inspected by means of optical and scanning electron microscopy.
Complementary to the morphology study, the wetting behaviour of the surface structures for water and oil was examined intensively in terms of fluid transport and philic/-phobic nature. Additionally, with these results in hand, tribological tests investigating the wear resistance of the laser-induced nano- and microstructures were carried out. Our results demonstrate that the functionality of surface structures found in nature could be transferred to technologically relevant materials, such as steel, providing a huge potential for industrial applications for instance in friction and wear reduction.
Ultrashort laser pulses with durations in the fs- to ps-range were used for large area surface processing of steel aimed at mimicking the morphology and extraordinary wetting behaviour of bark bugs (Aradidae) found in nature. The processing was performed by scanning the laser beam across the surface of initially polished flat sample surfaces. A systematic variation of the laser processing parameters (peak fluence, scan velocity, line overlap) allowed the identification of different regimes associated with characteristic surface morphologies (laser-induced periodic surface structures (LIPSS), grooves, spikes, etc.). Additionally, we show that different laser processing strategies, varying laser wavelength, pulse duration and repetition rates, allowed to achieve a range of morphologies that resemble different structures found in bark bugs. For identifying the ideal combination of parameters for mimicking bug-like structures, the surfaces were inspected by optical and scanning electron microscopy.
Complementary to the morphology study, the wetting behaviour of the surface structures for water and oil was examined intensively in terms of philic/-phobic nature and fluid transport. With these results in hand, tribological tests were carried out investigating the wear resistance of the laser-induced nano- and microstructures. Our results demonstrate a route towards reproducing complex structures inspired by nature and their functional response in technologically relevant materials.
The frictional response of molybdenum bis(C11-14 branched and linear alkyl) carbamodithioate oxo thioxo complex (Mo-dttc) versus bismuth dimethyldithiocarbamate (Bi-dtc) and bismuth dodecylbenzene Sulfonate (Bi-ddbsa) slip-rolling under mixed/boundary lubrication (T=120°C, n=10 millions of cycles, P0max=2.25 GPa) in PAO-based formulation against three different steel alloys were compared.
The electrochemical behavior of UNS N08031 was investigated as a function of electrode potential in Green-Death solution at 40 °C. The UNS N08031 surface is in a stable passive state during cyclic potentiodynamic polarization without an initiation and/or propagation of localized corrosion. In potentiostatic polarization of UNS N08031 for 3600 s, passive current density increases with an increase in the passivation potential from 0.7 to 1.0 VSSE (silver/silver chloride reference electrode in saturated potassium chloride) Electrochemical impedance spectroscopy (EIS) and Mott-Schottky (M-S) analysis showed that a more defective n-type semiconductive passive film forms as the potential increases. X-ray photoelectron spectroscopy (XPS) revealed that passive film consists of mainly chromium and minor iron and nickel oxides. The mechanism of the defective passive film formation is discussed. The increase of the applied potential is considered to be a reason for the change in passive film stability.
Neutron cameras allow visualizing hydrogen distributions with radiographic or tomographic imaging methods in iron and steel.
The necessary contrast between hydrogen and iron stems from the high difference in the total neutron cross section of both elements. This allows e.g. the in situ measurement of hydrogen mass flow inside cm thick steel samples with a temporal resolution of 20 s using neutron radiography as well as the quantitative measurement of hydrogen accumulations at the crack’s inner surfaces in hydrogen embrittled iron samples with neutron tomography. We could detect directly gaseous hydrogen in the crack cavities and we measured the gas pressure. This new quality of the information on a micrometer scale allows new insights for the analysis of hydrogen-induced damage mechanisms. Further, this method is non-destructive and provides local information in situ and in three dimensions with a spatial resolution of 20-30 μm.
In this contribution, we show examples that demonstrate the spatial and temporal resolution of the neutron radiography and tomography methods in order to visualize and quantify hydrogen accumulations at cracks. The measurements were performed
at the research reactor BER II of the HZB in Berlin and at the FRM II reactor of the neutron source Heinz Maier-Leibnitz in
Garching.
Steel tension rod systems consist of tension rods, fork connectors and associated intersection or connecting plates. They are used for truss systems, bracings or suspensions owing to slender design and increased economic efficiency. In case of fire, beside the tension rods themselves, the connection parts require appropriate fire protection. The use of intumescent fire protection coatings prevents a rapid heating of the steel and helps to ensure the load-carrying capacity of the structures. Because the connection components of the tension rod systems feature surface curvature as well as a complex geometry, high demand is placed on the intumescence and thermal protection effectiveness of the reactive fire protection coatings. Experimental studies were carried out to investigate the performance of intumescent coatings applied to the components of tension rod systems. The examined aspects include the foaming and cracking behaviour of the intumescent coatings, the influence of different dry film thicknesses (DFT), the heating rate of the steel connecting parts in comparison to the tension rods, as well as the mounting orientation of the tension rods together with their associated fork connectors. The results show that a decrease in the surface curvature and/or an increase in the mass concentration of the steel components lead to a lower heating rate of the steel. Moreover, the performance of the intumescent coating on tension rod systems is influenced by the mounting orientation of the steel components.