Ingenieurwissenschaften und zugeordnete Tätigkeiten
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- 2004 (5) (entfernen)
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- Orientation relationship (2)
- Austenitic stainless steels (1)
- Carrier gas (1)
- Duplex steel (1)
- EBSD (1)
- Electron backscatter diffraction (1)
- Extraction method (1)
- Hybrid (1)
- ISO 3690 (1)
- Iron meteorite (1)
As an approach towards more rough industrial laser welding applications, the Nd:YAG laser welding process has been coupled to the plasma powder welding process for the first time. Process stabilities have been achieved by such hybrid welding which are even better than those known from previous coupling of the laser process with gas metal arc welding (GMAW), for instance.
The present contribution focuses on the technology and potentials of the novel laser hybrid welding technique and addresses the realisation and the perspectives for practical applications. The experimental results demonstrate that the new process coupling enables welding of austenitic stainless steels in the thickness range between 3 mm and 8 mm at various weld geometries and joint configurations and at welding speeds exceeding 2 m/min. In addition it has been proven that the laser plasma powder arc welding (LPPAW) technique can also be applied to out-of-position conditions. Continuous advancement of the welding equipment ensures a high gap bridging ability and levelling of misalignment due to higher powder feeding rates. The recent development of a new plasma powder torch even provides a higher efficiency of powder feeding and guarantees smoth weld surfaces. Up to the present, the investigations demonstrated that the novel laser plasma powder hybrid welding technique offers all perspectives for application in pipe fabrication, ship building and offshore as well as transportation industry.
Is it reasonable to restrict ISO 3690 any longer to the determination of the weld metal hydrogen content of ferritic steel?
In what respect is the determination of the content of the diffusible and of the total hydrogen content, respectively, (still) merely a research task (supermartensite, duplex materials, austenite, magnesium, aluminium), or is there actually a demand in industry and is there already a first cause for monitoring in view of damage prevention, respectively?
Is there a need, arising from the development of materials and filler materials and from their intended applications, for more extensive standards dealing with hydrogen analyses for these materials?
Which parts of ISO 3690 could also be applied to any other metallic material/filler material, if necessary, and where would a complete alteration be required, respectively?
The orientation relationship (OR) between the bcc and fcc phase in the plessite microstructure of the iron meteorites Watson, Agpalilik and Gibeon has been analysed in a scanning electron microscope using electron back-scattered diffraction (EBSD). A very strong OR exists, independently on the analysed plessite type and the observed spreading of single orientation data. The agreement between the experimental orientation distribution and existing models varies for each meteorite. The black plessite in the Agpalilik corresponds to the Nishiyama-Wassermann model whereas the Duplex plessite of the Gibeon meteorite shows an OR close to the Kurdjumov-Sachs model. The Watson meteorite is strongly deformed so that a general OR is difficult to determine due to the blurred experimental orientation distribution.
Characterization of the fcc/bcc orientation relationship by EBSD using pole figures and variants
(2004)
The orientation relationship (OR) between fcc and bcc lattices are described by crystallographic fundamentals using the example of Kurdjumov-Sachs (K-S) and Nishiyama-Wassermann (N-W). Complete pole figures containing all variants will be used to distinguish even between slightly different ORs. EBSD on iron meteorites and duplex steel has been used to analyse a large number of crystal orientations with regard to a high statistical significance and a high probability to capture all variants in a single measurement. It is shown that the use of fixed OR models like K-S, N-W, Bain, Pitsch, or Greninger-Troiano does not satisfacturally reflect the observed experimental pole distributions. It is not convenient to use high-indexed lattice planes and directions to describe the small deviations from the given models. The Euler subspace representation offers a readily comprehensible tool to get an idea about the characteristic of the experimentally detected OR.
Novel fibre optic sensor (FOS) systems maintaining fibre Bragg gratings (FBG) are finding wide application for health monitoring of large-scale structures such as dams, bridges, towers, as well as aircrafts, robots, automotive vehicles, and in composite technology. The principal advantage of such type of sensors is that the measured information is wavelength encoded (an absolute quantity). The main advantages include small size, immunity against electromagnetic field, good resolution, high sensitivity, and possibility to work in adverse environment. Especially small dimensions of the sensor allow its application for investigation of composite materials. The use of sensors enables to get information in areas, where other sensors would affect the structure or the material. On the other hand, it is important to keep signal stability of the sensor to the measured value of interest and obtain reliable data. Intimate embedment produces, however, additional perturbations affecting optical fibre sensor such as general mechanical stress, microbending, bending, and point-wise transverse load, which result in such undesirable sensor signal changes as attenuation, birefringence, spectrum broadening, sideband increasing, or small wavelength shift. No reliable knowledge about those effects and their consequences to the measured signal could be found in literature. This lack of knowledge led to the motivation of this work. The thesis discusses behaviour of uniform short-period fibre Bragg grating signal under before mentioned perturbing influences. The main accent is made onto theoretical and experimental study of additional mechanical perturbations: point-wise transverse indentation, and microbending, arising at sensor operation depending on the grating integration type and measurement purpose. Response of this type of gratings (unapplied and integrated in/on the object to be mesaured) to the axial strain and composite-integrated gratings to the temperature is also investigated. Problems arising from the sensor fixing on/in the object to be measured are considered.