|
| ||
|
|
||
Acoustic Emission (acoustic + emission)
Selected AbstractsEffects of Fiber Architecture on Matrix Cracking for Melt-Infiltrated SiC/SiC CompositesINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 3 2010Gregory N. Morscher The matrix cracking behavior of slurry cast melt-infiltrated SiC matrix composites consisting of Sylramic-iBN fibers with a wide variety of fiber architectures were compared. The fiber architectures included 2D woven, braided, 3D orthogonal, and angle interlock architectures. Acoustic emission was used to monitor in-plane matrix cracking during unload,reload tensile tests. Two key parameters were found to control matrix-cracking behavior: the fiber volume fraction in the loading direction and the area of the weakest portion of the structure, that is, the largest tow in the architecture perpendicular to the loading direction. Empirical models that support these results are presented and discussed. [source] Paired comparisons for the evaluation of crispness of cereal flakes by untrained assessors: correlation with descriptive analysis and acoustic measurementsJOURNAL OF CHEMOMETRICS, Issue 3 2005Philippe Courcoux Abstract This study investigates the effectiveness of the paired comparison method in the evaluation of a complex sensory attribute by untrained assessors. The crispness perception of cereal flakes by a panel of 100 consumers is measured using a complete block design, and the fitting of the Bradley,Terry,Luce model leads to a ranking of the samples on a crispness intensity scale. A log,linear formulation of the Bradley model provides insight into goodness-of-fit tests and allows the effects of covariates to be incorporated in the prediction of the sensory scores. Results show a high correlation between crispness assessment by consumers and rating of texture attributes by trained assessors. Acoustic emission is shown to have a significant effect on crispness perception, and the power spectra of signals recorded during compression provide a prediction of the crispness of cereal flakes. Copyright © 2005 John Wiley & Sons, Ltd. [source] Degradation of repaired denture base materials in simulated oral fluidJOURNAL OF ORAL REHABILITATION, Issue 3 2000C.-T. Lin This in vitro study evaluates the degradation of repaired denture bases upon immersion in a simulated oral fluid. Denture base materials (Luciton 199®), after being repaired by Repair Material® and Triad®, using three different joint surface designs (butt, round and 45 ° bevel), were immersed onto 99·5 vol.% ethanol/water solution (with similar solubility parameter) for various amounts of time (0,72 h). The flexural loads of the six combination of groups were measured by the three-point bending tests using a universal testing machine. Acoustic emission (AE) during sample fracturing were processed using the MISTRA 2001 system. The fracture pattern and surface details of the interface were examined with a scanning electronic microscope (SEM). Data were analysed using three-way anova and Tukey LSD tests. SEM micrographs of the fracture interface were used to differentiate the fracture mode. The flexural loads (2·72±0·51 Kgf) of the round joint specimens were significantly higher (P<0·05) than those (butt: 1·66±0·38 Kgf, 45 ° bevel: 1·93±0·41 Kgf) of the other two designs. This corresponds to the microscopic examination in which more cohesive failure mode was found for the round joint group after storage. The flexural loads (2·54±0·39 Kgf) of the specimens repaired with Triad® were significantly higher (P<0·05) than those (1·59±0·40 Kgf) of specimens repaired with Repair Material®. Significant progressive reduction of the flexural load and/or AE signals of the specimens was noted in proportion to the length of time of the immersion in the simulated oral fluid. Mechanical strength of a denture base repaired with a round joint design and light-cured material is significantly higher after immersion in simulated oral fluid. [source] Correlation between microbubble contrast,enhanced color doppler sonography and immunostaining for Kupffer cells in assessing the histopathologic grade of hepatocellular carcinoma: Preliminary resultsJOURNAL OF CLINICAL ULTRASOUND, Issue 8 2002Hiroshi Kitamura MD Abstract Purpose The aim of this study was to determine the histopathologic grades of hepatocellular carcinomas (HCCs) on the basis of the presence of Kupffer cells, using color Doppler sonography with the liver-specific microbubble contrast agent Levovist. Methods Color Doppler sonograms generated by stimulated acoustic emission were obtained 7 minutes after intravenous injection of 5 ml of Levovist (300 mg/dl) in patients with histopathologically confirmed HCCs. CT scans were also obtained and evaluated, and hematoxylin and eosin staining for morphologic examination and immunostaining (anti-CD68) for detecting Kupffer cells were performed for confirmation of the sonographic findings. Results Eighteen tumors had a defect in the color Doppler signal (color void) that corresponded with the baseline gray-scale image of the tumor. On histopathologic examination, these 18 tumors were all found to be either poorly or moderately differentiated HCCs with either a marked reduction in the number of or the absence of Kupffer cells. The remaining 2 tumors showed color signals. Histopathologic examination of these 2 tumors disclosed well-differentiated components within the tumors, with Kupffer cells in the tumor tissue. Conclusions Color Doppler sonography using a liver-specific microbubble ultrasound contrast agent appears to reflect the histopathologic features of HCCs and may thus be useful for differentiating liver tumors and determining a treatment strategy. © 2002 Wiley Periodicals, Inc. J Clin Ultrasound 30:465,471, 2002; Published online in Wiley InterScience (www. interscience.wiley.com). DOI: 10.1002/jcu.10099 [source] Characterization of flow regime transition and particle motion using acoustic emission measurement in a gas-solid fluidized bedAICHE JOURNAL, Issue 5 2010Wang Jingdai Abstract Particle motion is a major determinant of the dynamical performance of a fluidized bed. It plays an important role in determining and optimizing the complex correlation of fluidization condition between particle-particle and particle-environment in a system. A passive acoustic emission (AE) technique is applied to monitor, characterize, and control the fluidization condition of polyethylene particles in a gas-solid fluidized bed. Experimental results show that AE signals are very sensitive to the particle movements by analyzing energy distribution, which can help to understand the status of the system. The AE energy temporal analysis is further used to identify the transition of flow regimes. Moreover, the activity of particle motion can be quantitatively determined by using a combination of granular temperature and AE spatial energy analysis. This work provides valuable insights into the dynamic behavior of particles in a gas-solid fluidized bed based on AE technique. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Resolution of structure characteristics of AE signals in multiphase flow system,From data to informationAICHE JOURNAL, Issue 10 2009Yi-Jun He Abstract This investigation was performed to study the underlying structure characteristics of acoustic emission (AE) signals, which could be helpful not only to understand a relatively complete picture of hydrodynamics in multiphase flow systems, but also to extract the most useful information from the original signals with respect to a particular measurement requirement. However, due to AE signals are made up of emission from many acoustic sources at different scales, the resolution of AE signals is often very complicated and appears to be relatively poorly researched. In this study, the structure characteristics of AE signals measured both in gas,solid fluidized bed and liquid,solid stirred tank were researched in detail by resorting to wavelet transform and rescaled range analysis. A general criterion was proposed to resolve AE signals into three physical-related characteristic scales, i.e., microscale, mesoscale, and macroscale. Multiscale resolution of AE signals implied that AE signals in microscale represented totally the dynamics of solid phase and could be applied to measure particle-related properties. Furthermore, based on the structure characteristics of AE signals, useful features related to particles motion were extracted to establish two new prediction models, one for on-line measurements of particle size distribution (PSD) and average particle size in gas,solid fluidized bed and the other for on-line measurement of the suspension height in liquid,solid stirred tank. The prediction results indicated that (1) measurements of PSD and average particle size using AE method showed a fairly good agreement with that using sieve method both for laboratory scale and plant scale fluidized beds, and (2) measurements of the suspension height using AE method showed a fairly good agreement with that using visual method. The results thus validated that the extracted features based on analyses of structure characteristics of AE signals were very useful for establishing effective on-line measurement models with respect to some particular applications. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Deformation Mechanisms in Compression-Loaded, Stand-Alone Plasma-Sprayed Alumina CoatingsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2000Rodney W. Trice Cylindrical, stand-alone tubes of plasma-sprayed alumina were tested in compression in the axial direction at room temperature, using strain gauges to monitor axial and circumferential strains. The primary compression-loading profile used was cyclic loading, with monotonically increased peak stresses. Hysteresis was observed in the stress,strain response on unloading, beginning at a peak stress of 50 MPa. The modulus decreased as the maximum applied stress increased. The stress,strain response was only linear at low stresses; the degree of nonlinearity at high stresses scaled with the stress applied. One-hour dwells at constant stress at room temperature revealed a time-dependent strain response. Using transmission electron microscopy and acoustic emission to investigate deformation mechanisms, the stress,strain response was correlated with crack pop-in, growth, and arrest. It is proposed that the numerous defects in plasma-sprayed coatings, including porosity and microcracks, serve as sites for crack nucleation and/or propagation. As these small, nucleated cracks extend under the applied stress, they propagate nearly parallel to the loading direction along interlamellae boundaries. With increasing stress, these cracks ultimately link, resulting in catastrophic failure. [source] High-pressure short time behavior of traction fluidsLUBRICATION SCIENCE, Issue 1 2006Nobuyoshi Ohno Abstract The squeeze film formation ability of traction fluids is studied under impact load by dropping a steel ball-bearing against a flat anvil made of mild steel. The effect of the pressure,viscosity coefficient and of the viscosity is investigated for plastic impact. The depth difference between the lubricated surface dent and the dry dent increases linearly with the product ,, of the pressure,viscosity coefficient , and the viscosity ,. The importance of the lubricant parameter ,, is observed under the squeeze film formation ability from contact voltage or elastohydrodynamic lubrication central film thickness measurement at rolling condition. The intensity of each impact collision is measured by means of an acoustic emission (AE) sensor. The high-pressure short-time solidification of traction fluids was confirmed by dent analysis after the impact tests and AE analysis under impact loads. Copyright © 2006 John Wiley & Sons, Ltd. [source] Influence of Temperature and Relative Humidity on the Friction and Wear of Unlubricated Reciprocating Sliding Steel/ Steel CouplesLUBRICATION SCIENCE, Issue 4 2004D. Klaffke Abstract Many tribosystems are subjected to different conditions with respect to temperature and humidity. Reciprocating sliding tests with steel/steel couples were performed using a laboratory test rig in air with varying relative humidity and temperature. During each test the friction force, the total linear wear, the electrical contact resistance, and the acoustic emission were recorded. Tests with self-mated couples of bearing steel (100r6) and of stainless steel (X10CrNiMoNb18-10/X5CrNi18-9) in a ball-on-disc arrangement revealed small effects of temperature and humidity on friction, but a strong effect of the water vapour content on the wear rate of the system. Attempts were made to correlate changes of wear behaviour with different wear mechanisms. [source] Entry dynamics and acoustics/infrasonic/seismic analysis for the Neuschwanstein meteorite fallMETEORITICS & PLANETARY SCIENCE, Issue 10 2004D. O. REVELLE This includes ground-based photographic and radiometer data as well as infrasound and seismic data from this very significant bolide event (Spurný et al. 2002, 2003). We have also used these data to model the entry of Neuschwanstein, including the expected dynamics, energetics, panchromatic luminosity, and associated fragmentation effects. In addition, we have calculated the differential efficiency of acoustical waves for Neuschwanstein and used these values to compare against the efficiency calculated using available ground-based infrasound data. This new numerical technique has allowed the source height to be determined independent of ray tracing solutions. We have also carried out theoretical ray tracing for a moving point source (not strictly a cylindrical line emission) and for an infinite speed line source. In addition, we have determined the ray turning heights as a function of the source height for both initially upward and downward propagating rays, independent of the explicit ray tracing (detailed propagation path) programs. These results all agree on the origins of the acoustic emission and explicit source heights for Neuschwanstein for the strongest infrasonic signals. Calculated source energies using more than four different independent approaches agree that Neuschwanstein was certainly <500 kg in initial mass, given the initial velocity of 20.95 km/s, resulting in an initial source energy ,0.0157-0.0276 kt TNT equivalent (4.185 times 1012 J). Local source energies at the calculated infrasonic/seismic source altitudes are up to two orders of magnitude smaller than this initial source energy. [source] Helioseismic analysis of the solar flare-induced sunquake of 2005 January 15MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2007H. Moradi ABSTRACT We report the discovery of one of the most powerful sunquakes detected to date, produced by an X1.2-class solar flare in active region AR10720 on 2005 January 15. We used helioseismic holography to image the source of seismic waves emitted into the solar interior from the site of the flare. Acoustic egression power maps at 3 and 6 mHz with a 2-mHz bandpass reveal a compact acoustic source strongly correlated with impulsive hard X-ray and visible-continuum emission along the penumbral neutral line separating the two major opposing umbrae in the ,-configuration sunspot that predominates AR10720. At 6 mHz the seismic source has two components, an intense, compact kernel located on the penumbral neutral line of the ,-configuration sunspot that predominates AR10720, and a significantly more diffuse signature distributed along the neutral line up to ,15 Mm east and ,30 Mm west of the kernel. The acoustic emission signatures were directly aligned with both hard X-ray and visible continuum emission that emanated during the flare. The visible continuum emission is estimated at 2.0 × 1023 J, approximately 500 times the seismic emission of ,4 × 1020 J. The flare of 2005 January 15 exhibits the same close spatial alignment between the sources of the seismic emission and impulsive visible continuum emission as previous flares, reinforcing the hypothesis that the acoustic emission may be driven by heating of the low photosphere. However, it is a major exception in that there was no signature to indicate the inclusion of protons in the particle beams thought to supply the energy radiated by the flare. The continued strong coincidence between the sources of seismic emission and impulsive visible continuum emission in the case of a proton-deficient white-lightflare lends substantial support to the ,back-warming' hypothesis, that the low photosphere is significantly heated by intense Balmer and Paschen continuum-edge radiation from the overlying chromosphere in white-light flares. [source] An acoustic emission study on the fracture behavior of continuous glass fiber/polypropylene composites based on commingled yarnPOLYMER COMPOSITES, Issue 7 2008Yantao Wang The fracture behavior of continuous glass fiber reinforced polypropylene composites made of commingled yarn in the form of biaxial (±±45°) noncrimp warp-knitted fabric, twill woven fabric, and swirl mat, respectively, was investigated by virtue of single edge notched tensile (SEN-T) specimens. These composite laminates were manufactured by compression molding and cooled at two different rates (1°C/min and 10°C/min) during the last processing phase of the laminates. The failure mechanisms were studied by acoustic emission (AE) analysis. AE amplitude ranges corresponding to the individual failure modes have been identified. For biaxial noncrimp fabric reinforced materials, the failure mechanisms involved in the fracture procedure are governed by the interface related failure events. Higher cooling rate, which is accompanied by better fiber/matrix adhesion, results in not only the increase in the relative proportion of high-amplitude failure events, but also the occurrence of a large quantity of fiber fracture events. For woven fabric and mat reinforced composites, fiber-dominated failure mechanisms result in the higher fracture toughness when compared with biaxial noncrimp fabric composites. Under this circumstance, the change in cooling rate only results in the difference in the relative frequency of the individual failure modes. In addition, it is found out that the initiation fracture toughness of SEN-T specimens can be easily assessed by marking the load value which corresponds to the first point of AE signals emitted stably in AE events-displacement curves. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers [source] Fracture and failure behavior of fabric-reinforced all-poly(propylene) composite (Curv®),POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 2 2007Gábor Romhány Abstract The in-plane static fracture of a fabric reinforced all-poly(propylene) (all-PP, Curv®) composite was studied at ambient temperature using the concept of the linear elastic fracture mechanics. The apparent fracture toughness was determined on single-edge notched tensile specimens (SEN-T) considering the maximum load. The related values did not differ much from those determined by the resistance curve (KR) method. The crack growth, requested to construct the KR curves, was traced by the movement in the center of gravity of the cumulative amplitude of the located acoustic emission (AE) events. The quality of consolidation of the all-PP composite was reflected by the force-displacement curve (appearance of pop-in), course of the cumulative AE events during loading, extension and change of the estimated damage zone during fracture. The failure behavior was studied also by fractography and is discussed. Copyright © 2006 John Wiley & Sons, Ltd. [source] A New Method to Identify Quaternary Moraine: Acoustic Emission Stress MeasurementACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 5 2006ZHAO Zhizhong Abstract: How to effectively identify glacial sediments, especially Quaternary moraine, has been in dispute for decades. The traditional methods, e.g., sedimentary and geomorphologic ones, are facing challenge in eastern China where controversial moraine deposits are dominatingly distributed. Here, for the first time, we introduce the acoustic emission (AE) stress measurement, a kind of historical stress measurement, to identify Quaternary moraine. The results demonstrate that it can be employed to reconstruct stress information of glaciation remaining in gravels, and may shed light on the identification of Quaternary moraine in eastern China. First, we measured the AE stress of gravels of glacial origin that are underlying the Xidatan Glacier, eastern Kunlun Mountains in western China. Second, we calculated the stress according to the actual thickness of the glacier. The almost identical stress values suggest that the glacial gravels can memorize and preserve the overlying glacier-derived aplomb stress. And then we introduce this new approach to the controversial moraine in Mount Lushan, eastern China. The results indicate that the stress is attributed to the Quaternary glacier, and the muddy gravels in the controversial moraine in Mount Lushan are moraine deposits but not others. [source] Ultrasound contrast enhancing agents in neurosonology: principles, methods,future possibilitiesACTA NEUROLOGICA SCANDINAVICA, Issue 1 2000D. W. Droste Objectives, Ultrasound of the brain supplying arteries is a standard diagnostic procedure in patients with suspected and definite acute and chronic cerebrovascular occlusive disease. Anatomical and pathological limitations led to the development of echocontrast agents which are able to survive pulmonary and capillary transit and improve the echogenicity of the flowing blood. Material and Methods, This article reviews present and future applications of echocontrast agents in conjunction with personal experiences. Results, Currently, echocontrast is used for the differentiation of internal carotid artery occlusion and pseudoocclusion, better delineation of the maximal narrowing in high-grade stenoses, and better visualization of the extracranial vertebral artery and its collaterals. Transcranial applications include the insufficient foraminal or temporal window, assessment of arteriovenous malformations, thrombosis of cerebral veins and sinuses, and intracranial aneurysms. The use of echocontrast can have direct diagnostic and therapeutic consequences. Harmonic imaging, perfusion imaging, stimulated acoustic emission, and drug delivery are possible future domains of the technique. Discussion, Besides the support of conventional neurovascular ultrasound in poor examination conditions due to the patients' anatomy or pathology, echocontrast agents may allow for novel applications in the diagnosis and treatment of cerebrovascular patients. [source] Tests on the vibro-acoustic behaviour of a brushless DC-motorEUROPEAN TRANSACTIONS ON ELECTRICAL POWER, Issue 5 2000W. Heylen In the design of rotating electrical machines, the vibro-acoustic behaviour becomes an important criterion. In an electrical machine, electromagnetically induced forces may cause vibrations of, for instance, the stator. These vibrations may radiate annoying acoustic energy, especially at resonances of the stator assembly. This paper describes some techniques to analyse the vibro-acoustic behaviour of a (brushless DC-) motor. However, the technique is quite general and can be used for all types of electrical machines. The "inverse-frequency-response-function" technique (I FRF) allows the identification of the actual vibration behaviour of the motor frame from the measurement of the acoustic field around the motor. Experimental modal analysis yields the resonant behaviour of the motor. A combination of both techniques indicates the critical resonances, causing the undesired acoustic emissions. This may lead to an improved, quieter design of the electrical motor. [source] Freeze,thaw-induced embolism in Pinus contorta: centrifuge experiments validate the ,thaw-expansion hypothesis' but conflict with ultrasonic emission dataNEW PHYTOLOGIST, Issue 4 2010Stefan Mayr Summary ,The ,thaw-expansion hypothesis' postulates that xylem embolism is caused by the formation of gas bubbles on freezing and their expansion on thawing. We evaluated the hypothesis using centrifuge experiments and ultrasonic emission monitoring in Pinus contorta. ,Stem samples were exposed to freeze,thaw cycles at varying xylem pressure (P) in a centrifuge before the percentage loss of hydraulic conductivity (PLC) was measured. Ultrasonic acoustic emissions were registered on samples exposed to freeze,thaw cycles in a temperature chamber. ,Freeze,thaw exposure of samples spun at ,3 MPa induced a PLC of 32% (one frost cycle) and 50% (two cycles). An increase in P to ,0.5 MPa during freezing had no PLC effect, whereas increased P during thaw lowered PLC to 7%. Ultrasonic acoustic emissions were observed during freezing and thawing at ,3 MPa, but not in air-dried or water-saturated samples. A decrease in minimum temperature caused additional ultrasonic acoustic emissions, but had no effect on PLC. ,The centrifuge experiments indicate that the ,thaw-expansion hypothesis' correctly describes the embolization process. Possible explanations for the increase in PLC on repeated frost cycles and for the ultrasonic acoustic emissions observed during freezing and with decreasing ice temperature are discussed. [source] Differences in hydraulic architecture account for near-isohydric and anisohydric behaviour of two field-grown Vitis vinifera L. cultivars during droughtPLANT CELL & ENVIRONMENT, Issue 8 2003H. R. SCHULTZ ABSTRACT A comparative study on stomatal control under water deficit was conducted on grapevines of the cultivars Grenache, of Mediterranean origin, and Syrah of mesic origin, grown near Montpellier, France and Geisenheim, Germany. Syrah maintained similar maximum stomatal conductance (gmax) and maximum leaf photosynthesis (Amax) values than Grenache at lower predawn leaf water potentials, ,leaf, throughout the season. The ,leaf of Syrah decreased strongly during the day and was lower in stressed than in watered plants, showing anisohydric stomatal behaviour. In contrast, Grenache showed isohydric stomatal behaviour in which ,leaf did not drop significantly below the minimum ,leaf of watered plants. When g was plotted versus leaf specific hydraulic conductance, Kl, incorporating leaf transpiration rate and whole-plant water potential gradients, previous differences between varieties disappeared both on a seasonal and diurnal scale. This suggested that isohydric and anisohydric behaviour could be regulated by hydraulic conductance. Pressure-flow measurements on excised organs from plants not previously stressed revealed that Grenache had a two- to three-fold larger hydraulic conductance per unit path length (Kh) and a four- to six-fold larger leaf area specific conductivity (LSC) in leaf petioles than Syrah. Differences between internodes were only apparent for LSC and were much smaller. Cavitation detected as ultrasound acoustic emissions on air-dried shoots showed higher rates for Grenache than Syrah during the early phases of the dry-down. It is hypothesized that the differences in water-conducting capacity of stems and especially petioles may be at the origin of the near-isohydric and anisohydric behaviour of g. [source] | |||||||||||||||||||||||||