Ingenieurwissenschaften und zugeordnete Tätigkeiten
Filtern
Erscheinungsjahr
Dokumenttyp
- Beitrag zu einem Tagungsband (72) (entfernen)
Referierte Publikation
- ja (72) (entfernen)
Schlagworte
- Thermography (5)
- Additive manufacturing (4)
- Welding (4)
- Active thermography (3)
- Additive Manufacturing (3)
- FEM (3)
- Residual stress (3)
- Simulation (3)
- Ultrasound (3)
- Ageing (2)
Organisationseinheit der BAM
- 8 Zerstörungsfreie Prüfung (12)
- 8.0 Abteilungsleitung und andere (9)
- 9 Komponentensicherheit (7)
- 3 Gefahrgutumschließungen; Energiespeicher (4)
- 6 Materialchemie (4)
- 3.4 Sicherheit von Lagerbehältern (3)
- 8.5 Röntgenbildgebung (3)
- 9.4 Integrität von Schweißverbindungen (3)
- 5 Werkstofftechnik (2)
- 6.2 Material- und Oberflächentechnologien (2)
The industrial use of ultrashort laser pulses has made considerable progress in recent years. The reasons for this lie in the availability of high average powers at pulse repetition rates in the several 100 kHz range. The advantages of using ultrashort laser pulses in terms of processing precision can thus be fully exploited. However, high laser intensities on the workpiece can also lead to the generation of unwanted X-rays. Even if the emitted X-ray dose per pulse is low, the accumulated X-ray dose can become significant for high-repetition-rate laser systems so that X-ray exposure safety limits must be considered. The X-ray emission during ultrashort pulse laser processing was investigated for a pulse duration of 925 fs at 1030 nm wavelength and 400 kHz repetition rate. Industrially relevant materials such as steel,aluminum and glass were treated. Tungsten served as reference. X-ray spectra were recorded, and X-ray dose measurements were performed for laser treatment in air. For laser intensities > 2 × 10^13 W/cm2, X-ray doses exceeding the regulatory exposure limits for members of the public were found. Suitable X-ray protection strategies are proposed.
High-power laser beam welding became new stimuli within the last 10 years due to the availability of a new generation of high brightness multi kilowatt solid state lasers. In the welding research new approaches have been developed to establish reliable and praxis oriented welding processes meeting the demands of modern industrial applications during this time. The paper focuses on some of the current scientific and technological aspects in this research field like hybrid laser arc welding, simulation techniques, utilization of electromagnetic fields or reduced pressure environment for laser beam welding processes, which contributed to the further development of this technology or will play a crucial role in its further industrial implementation.
A composite material is a combination of two or more materials with very different mechanical, thermal and electrical properties. The various forms of composite materials, due to their high material properties, are widely used as structural materials in the aviation, space, marine, automobile, and sports industries. However, some defects like voids, delamination, or inhomogeneous fiber distribution that form during the fabricating processes of composites can seriously affect the mechanical properties of the composite material. In this study, several imaging NDE techniques such as: thermography, high frequency eddy current, ultrasonic, x-ray radiography, x-ray laminography, and high resolution x-ray CT were conducted to characterize the microstructure of carbon fiber composites. Then, a 3D analysis was implemented by the destructive technique of serial sectioning for the same sample tested by the NDE methods. To better analyze the results of this work and extract a clear volume image for all features and defects contained in the composite material, an intensive comparison was conducted among hundreds of 3D-NDE and multi serial sections’ scan images showing the microstructure variation.
During the energy transformation from fossil fuels to renewable energy sources, the use of hydrogen as fuel and energy storage can play a key role. This presents new challenges to industry and the scientific community alike. The storage and transport of hydrogen, which is nowadays mainly realized by austenitic stainless steels, remains problematic, which is due to the degradation of mechanical properties and the possibility of phase transformation by hydrogen diffusion and accumulation. The development of materials and technologies requires a fundamental understanding of these degradation processes. Therefore, studying the behavior of hydrogen in austenitic steel contributes to an understanding of the damage processes, which is crucial for both life assessment and safe use of components in industry and transportation. As one of the few tools that is capable of depicting the distribution of hydrogen in steels, time-of-flight secondary ion mass spectrometry was conducted after electrochemical charging. To obtain further information about the structural composition and cracking behavior, electron-backscattered diffraction and scanning electron microscopy were performed. Gathered data of chemical composition and topography were treated employing data fusion, thus creating a comprehensive portrait of hydrogen-induced effects in the austenite grade AISI 304L. Specimens were electrochemically charged with deuterium instead of hydrogen. This arises from the difficulties to distinguish between artificially charged hydrogen and traces existing in the material or the rest gas in the analysis chamber. Similar diffusion and permeation behavior, as well as solubility, allow nonetheless to draw conclusions from the experiments.
We demonstrate narrow band spectral intensity switching in dual-core photonic crystal fibers made of highly nonlinear glass under femtosecond excitation. The fibers expressed dual-core asymmetry, thus the slow and fast fiber cores were unambiguously distinguished according to their dispersion profiles. The asymmetry effect on the dual-core Propagation in anomalous dispersion region was studied both experimentally and numerically. The experimental study was carried
out using femtosecond laser amplifier system providing tunable pulses in range of 1500 nm - 1800 nm. The obtained results unveiled, that it is possible to improve nonlinearly the coupling between the two waveguides by excitation of the fast fiber core. The results were obtained in regime of high-order soliton propagation and were verified numerically by the coupled generalized nonlinear Schrödinger equations model. The spectral analysis of the radiation transferred to the non-excited core revealed the role of effects such as third order dispersion, soliton compression and spectral dependence of the coupling efficiency. The simulation results provide reasonable agreement with the experimentally observed spectral evolutions in the both fiber cores. Under 1800 nm excitation, narrow band spectral intensity switching was registered with contrast of 23 dB at 10 mm fiber length by changing the excitation pulse energy in sub-nanojoule range.
Due to the rapid thermal cycles involved in additive manufacturing of metals, high internal stresses and peculiar microstructures occur, which influence the parts mechanical properties. To systematically examine their formation, in-process measurements of the temperature are needed. Since the part emissivity is strongly inhomogeneous and rapidly changing in the process, the applicability of thermography for the determination of thermodynamic temperatures is limited. Measuring the thermal radiation in different wavelengths simultaneously, temperature and emissivity can be separated. Here, we present results of a preliminary study using multispectral thermography to obtain real temperatures and emissivities in directed energy deposition (DED) processes.
In this paper we present results of our recent efforts to understand the mechanical interface behaviour of single-walled carbon nanotubes (CNTs) embedded in metal matrices. We conducted experimental pull-out tests of CNTs embedded in Pd or Au and found Maximum forces in the range 10 - 102 nN. These values are in good agreement with forces obtained from molecular Dynamics simulations taking into account surface functional Groups (SFGs) covalently linked to the CNT material. The dominant failure mode in experiment is a CNT rupture, which can be explained with the presence of SFGs. To qualify the existence of SFGs on our used CNT material, we pursue investigations by means of fluorescence labeling of surface species in combination with Raman imaging. We also report of a tensile test system to perform pull-out tests inside a transmission electron microscope to obtain in situ images of CNT-metal interfaces under mechanical loads at the atomic scale.
In this paper, we present a study aimed at characterizing the optimal fiber optic components for Brillouin sensing in multimode fibers. For this purpose the use of single-mode and multimode circulators as well as couplers typically used in the Brillouin measurement setups was investigated. On the one hand the undesired coupling losses between conventional fiber optic measurement system components and a multimode sensor fiber can be overcome by replacing the singlemode components with their own multimode equivalents. On the other hand the use of multimode fiber optic circulators and multimode couplers affects the mode distribution of laser light which can impair the measurement signal backscattered in the multimode sensor fibers. In view of an increasing interest in high strain measurements using polymer optical fibers (POFs) as Brillouin-distributed sensors the investigation on Brillouin scattering effects in multimode fibers (MMFs) was performed on a low-loss perfluorinated graded-index polymer optical fiber (PFGI-POF). The obtained results were compared with those of a standard graded-index multimode (GI-MMF) silica glass optical fiber (GOF).
This study confirms the relevance of the adaptation of the measurement system components to the use of the multimode sensor fibers. In addition, due to mode coupling effects occurring in the tested POF itself, the results show differences in the yield of the components adaptation in the sensory implementation of the two kinds of the tested optical fibers.
THz and mid IR spectroscopy of high-molecular PE (HMW) and ultra high-molecular PE (UHMW) reveals modifications of the molecular structure. Characteristic absorption bands are changed if the two materials are exposed by γ-Co60 radiation up to 600 kGy and subsequently stored at an annealing temperature of 398 K until for 729 days.