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RISS 인기검색어
- 검색키워드
- 저자 : Fasel, Claudia (검색결과 4 건)
- 무료
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Damage state evaluation of experimental and simulated bolted joints using chaotic ultrasonic waves
Fasel, T.R.,Kennel, M.B.,Todd, M.D.,Clayton, E.H.,Park, G. Techno-Press 2009 Smart Structures and Systems, An International Jou Vol.5 No.4
Ultrasonic chaotic excitations combined with sensor prediction algorithms have shown the ability to identify incipient damage (loss of preload) in a bolted joint. In this study we examine a physical experiment on a single-bolt aluminum lap joint as well as a three-dimensional physics-based simulation designed to model the behavior of guided ultrasonic waves through a similarly configured joint. A multiple bolt frame structure is also experimentally examined. In the physical experiment each signal is imparted to the structure through a macro-fiber composite (MFC) patch on one side of the lap joint and sensed using an equivalent MFC patch on the opposite side of the joint. The model applies the waveform via direct nodal displacement and 'senses' the resulting displacement using an average of the nodal strain over an area equivalent to the MFC patch. A novel statistical classification feature is developed from information theory concepts of cross-prediction and interdependence. This damage detection algorithm is used to evaluate multiple damage levels and locations.
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Damage state evaluation of experimental and simulated bolted joints using chaotic ultrasonic waves
T. R. Fasel,M. B. Kennel,M. D. Todd,E. H. Clayton,G. Park 국제구조공학회 2009 Smart Structures and Systems, An International Jou Vol.5 No.4
Ultrasonic chaotic excitations combined with sensor prediction algorithms have shown the ability to identify incipient damage (loss of preload) in a bolted joint. In this study we examine a physical experiment on a single-bolt aluminum lap joint as well as a three-dimensional physics-based simulation designed to model the behavior of guided ultrasonic waves through a similarly configured joint. A multiple bolt frame structure is also experimentally examined. In the physical experiment each signal is imparted to the structure through a macro-fiber composite (MFC) patch on one side of the lap joint and sensed using an equivalent MFC patch on the opposite side of the joint. The model applies the waveform via direct nodal displacement and ‘senses’ the resulting displacement using an average of the nodal strain over an area equivalent to the MFC patch. A novel statistical classification feature is developed from information theory concepts of cross-prediction and interdependence. This damage detection algorithm is used to evaluate multiple damage levels and locations.
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High-temperature oxidation behavior of polymer-derived SiHfBCN ceramic nanocomposites
Yuan, J.,Galetz, M.,Luan, X.G.,Fasel, C.,Riedel, R.,Ionescu, E. Elsevier Science Publishers 2016 Journal of the European Ceramic Society Vol.36 No.12
Within this study, the oxidation behavior of SiHfBCN ceramic powders and monoliths was studied at temperatures from 1200 to 1400<SUP>o</SUP>C. Both powder and monolithic samples exhibited parabolic oxidation behavior characterized by very low rates (10<SUP>-9</SUP>-10<SUP>-8</SUP>mg<SUP>2</SUP>cm<SUP>-4</SUP>h<SUP>-1</SUP>). The activation energy of 112.9kJmol<SUP>-1</SUP>, which was determined for the SiHfBCN powder, is comparable to that of other silica formers such as silicon or SiC and relates to the diffusion of molecular oxygen through silica scale. Whereas, the values determined for the SiHfBCN ceramic monoliths (174 and 140kJmol<SUP>-1</SUP>, depending on the Hf content) indicate the complex nature of their oxidation process, leading at temperatures below 1300<SUP>o</SUP>C to a continuous oxide scale consisting of borosilicate, silica, m-and t-HfO<SUB>2</SUB>. At higher temperatures, the oxide scale consists of silica, HfSiO<SUB>4</SUB> as well as m-and t-HfO<SUB>2</SUB> and becomes discontinuous, probably due to the evaporation of boria.
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Yuan, Jia,Hapis, Stefania,Breitzke, Hergen,Xu, Yeping,Fasel, Claudia,Kleebe, Hans-Joachim,Buntkowsky, Gerd,Riedel, Ralf,Ionescu, Emanuel American Chemical Society 2014 Inorganic chemistry Vol.53 No.19
<P>Amorphous SiHfBCN ceramics were prepared from a commercial polysilazane (HTT 1800, AZ-EM), which was modified upon reactions with Hf(NEt<SUB>2</SUB>)<SUB>4</SUB> and BH<SUB>3</SUB>·SMe<SUB>2</SUB>, and subsequently cross-linked and pyrolyzed. The prepared materials were investigated with respect to their chemical and phase composition, by means of spectroscopy techniques (Fourier transform infrared (FTIR), Raman, magic-angle spinning nuclear magnetic resonance (MAS NMR)), as well as X-ray diffraction (XRD) and transmission electron microscopy (TEM). Annealing experiments of the SiHfBCN samples in an inert gas atmosphere (Ar, N<SUB>2</SUB>) at temperatures in the range of 1300–1700 °C showed the conversion of the amorphous materials into nanostructured UHTC-NCs. Depending on the annealing atmosphere, HfC/HfB<SUB>2</SUB>/SiC (annealing in argon) and HfN/Si<SUB>3</SUB>N<SUB>4</SUB>/SiBCN (annealing in nitrogen) nanocomposites were obtained. The results emphasize that the conversion of the single-phase SiHfBCN into UHTC-NCs is thermodynamically controlled, thus allowing for a knowledge-based preparative path toward nanostructured ultrahigh-temperature stable materials with adjusted compositions.</P><P>Amorphous SiHfBCN ceramics were prepared from a suitable single-source precursor. Annealing experiments of the SiHfBCN samples in an inert gas atmosphere at temperatures of 1300−1700 °C led to their conversion nanostructured UHTC-NCs, such as HfC/HfB<SUB>2</SUB>/SiC nanocomposites (in argon) and HfN/Si<SUB>3</SUB>N<SUB>4</SUB>/SiBCN nanocomposites (in nitrogen), thus revealing a convenient preparative approach to nanostructured ultrahigh-temperature stable materials starting from a greatly flexible single-source precursor.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/inocaj/2014/inocaj.2014.53.issue-19/ic501512p/production/images/medium/ic-2014-01512p_0016.gif'></P>
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