Ingenieurwissenschaften und zugeordnete Tätigkeiten
Filtern
Dokumenttyp
Referierte Publikation
- ja (6) (entfernen)
Schlagworte
- Absorption (1)
- Colour center (1)
- Ellipsometry (1)
- Etalon feature (1)
- FT-IR spectroscopy (1)
- Far-infrared spectroscopy (1)
- Irradiation (1)
- Modul (1)
- Optical layer analysis (1)
- Optical properties of dielectric materials (1)
Organisationseinheit der BAM
ür die Berücksichtigung mechanischer Belastungen unterhalb der Streckgrenze ist im Rahmen einer zuverlässigen Bauteilauslegung die Kenntnis der elastischen Konstanten von besonderer Bedeutung. Für die experimentelle Bestimmung des Elastizitätsmoduls wurde eine Vielzahl von Verfahren entwickelt, die zum Teil werkstoffspezifisch Eingang in die Normung gefunden haben.
Prinzipiell können diese Verfahren in zwei Gruppen unterteilt werden: die statischen und die dynamischen Prüfverfahren. Die statischen Verfahren beruhen auf der direkten Messung des Spannungs-Dehnungs-Zusammenhangs während einer mechanischen Belastung im elastischen Verformungsbereich (Zug, Biegung, Druck). Die dynamischen Verfahren basieren auf der Schwingungsanregung eines Prüfkörpers und der Analyse der resultierenden Schwingungen (Resonanzmethode oder Impulsanregungsmethode) oder auf der Messung der Ultraschallausbreitungsgeschwindigkeit.
Stellvertretend für die dynamischen Verfahren wird im ersten Teil dieses Beitrages die Resonanzmethode vorgestellt. Der zweite Teil dieses Beitrages fasst die werkstoffabhängigen Ergebnisse der E-Modulbestimmung mit statischen Verfahren im Zug- und Biegeversuch zusammen.
Removal of Etalon Features in the Far-Infrared–Terahertz Transmittance Spectra of Thin Polymer Films
(2020)
Etalon features in infrared spectra of stratified samples, their influence on the interpretation and methods to circumvent their presence in infrared spectra have been in discussion for decades. This paper focuses on the application of a method originally developed to remove interference fringes in the mid-infrared spectra for far-infrared Fourier transform spectroscopy on thin polymer films. We show that the total transmittance-reflectance technique, commonly used for mid-infrared, also works successfully in the far infrared spectral range where other approaches fail. Experimental spectra obtained by such technique are supported by model calculations and reveal the possibility and limits to obtain almost undisturbed far-infrared spectra which are suitable to determine low energy vibrations of ionomer salts under certain sample conditions.
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.
Discoloration Effects of High-Dose gamma-Irradiation and Long-Term Thermal Aging of (U) HMW-PE
(2017)
Two polyethylene types with ultra-high (UHMWPE) and high molecular weight (HMW-PE) used as neutron radiation shielding materials in casks for radioactive waste were irradiated with doses up to 600 kGy using a 60Co gammasource. Subsequently, thermal aging at 125∘C was applied for up to one year. Degradation effects in the materials were characterized using colorimetry, UV-Visspectroscopy, IR spectroscopy, and DSC. Both materials exhibited a yellowing upon irradiation.The discoloration of UHMW-PE disappeared again after thermal aging.Therefore, the yellowing is assumed to originate fromannealable color centers in the formof free radicals that are trapped in the crystalline regions of the polymer and recombine at elevated temperatures. For the antioxidantcontaining HMWPE, yellowing was observed after both irradiation and thermal aging. The color change was correlated mainly to decomposition products of the antioxidant in addition to trapped radicals as in UHMW-PE. Additionally, black spots appeared after thermal aging of HMW-PE.
THz – ToF optical layer analysis (OLA) to determine optical properties of dielectric materials
(2017)
Electromagnetic waves with frequencies between 0.1 and 10 THz are described as THz-radiation (T-ray). The ability to penetrate dielectric materials makes T-rays attractive to reveal discontinuities in polymer and ceramic materials.
THz-Time Domain Spectroscopy Systems (THz-TDS) are available on the market today which operates with THz-pulses transmitted and received by optically pumped semiconductor antennas. In THz-TDS the travelling time (ToF) and shape of the pulse is changed if it interacts with the dielectric material and its inherent discontinuities. A tomogram of the object under the test can be reconstructed from time of flight diffraction (ToFD) scans if a synthetic focusing aperture (SAFT) algorithm is applied. The knowledge of the base materials shape and optical properties is essential for a proper reconstruction result. To obtain these properties a model is assumed which describes the device under the test as multilayer structure composed of thin layers with different dielectric characteristics. The Optical Layer Analysis (OLA) is able to fulfill these requirements. A short description why the optical properties are crucial for meaningful SAFT reconstruction results will be given first. Afterwards the OLA will be derived and applied on representative samples to discuss and evaluate ist benefits and limits.
Optical constants of harmful and highly energetic liquids for application to THz screening systems
(2016)
The far-infrared (IR) optical constants of a set of hazardous and flammable liquids have been obtained by means of spectroscopic ellipsometry in attenuated total reflection configuration over a broad spectral range. Such liquids recently became of considerable concern for transportation security measures worldwide. Their optical identification at check-in gates can only become possible if the characteristic spectra are already known. The refractive indices and the extinction coefficients reported here contribute to a spectroscopic data base in the far-IR and terahertz (THz) spectral regions and may support modeling the performance of THz screening systems on liquids for airports and other security sensitive areas. Examples of several container material/liquid systems are discussed. From the measured optical constants typical THz waveforms are calculated and discussed.