1,721,060 research outputs found
Image Processing for Fringe Unwrapping in Speckle Interferometry
No full textAlthough Electronic Speckle Pattern Interferometry (ESPI) is a well known optical technique which can provide stationary vibration patterns with high spatial resolution, it has not yet became a widespread methodology in modal analysis and related areas such as system identification and updating. The main reason for such situation can be recognized in the difficulties of the retrieval of quantitative information about modal parameters from the fringe pattern images. In this paper an algorithm based on the Hilbert transform is presented, it is capable of extracting mode shapes from the fringe pattern images obtained by Time Average ESPI, which is the easiest procedure for applying ESPI to modal analysis. Starting from the paper which Hilbert was firstly adopted, the method has been applied to numerical examples of a cantilever beam and plate
Metal matrix composites based on aluminum and optical fibers
No full textEmbedding optical fibers into structural components is a very promising technology for real time health monitoring. Recently the interest for producing low cost and reliable sensors is increased in the mechanical, civil and aerospace engineering community. In this work aluminum and polyimide coated optical fibers have been successfully embedded in different aluminum alloys by using both cast and colamination techniques. The studied samples have been subjected to the following tests: mechanical test and optical transmission tests to highlight the fiber integrity after the embedding process; metallographic observation of the fiber/matrix interface. It is also reported a preliminary interferometric test to show that the embedded optical fiber can be usefully used as a global sensor for measuring variations of the physical properties of the hosting material. The possibility of embedding optical fibers in aluminum alloys has been demostrated
Characterization of Pseudomonas syringae ssp. savastanoi strains isolated from ash
No full textIsolates of Pseudomonas syringae ssp. savastanoi from ash were examined for their ability to produce phytohormones in culture and for pathogenicity, in comparison with isolates from olive and oleander. Nineteen out of 20 ash isolates produced low levels of indole-3-acetic acid and its methyl ester but no cytokinins. In contrast, the remaining isolate, NCPPB3474, accumulated high levels of auxins and cytokinins in culture, comparable to those of olive and oleander strains. Hybridization of DNA preparations with tryptophan mono-oxygenase (iaaM) and isopentenyl transferase (qt) gene-containing probes showed sequences of DNA homologous to both probes only in isolate NCPPB3474, and in which the iaaM and ipt genes were located on the chromosome and on a plasmid of about 80 kb, respectively. When assayed for pathogenicity on ash, olive and oleander, 19 of the 20 ash isolates caused disease only on ash but NCPPB3474 caused knots on both ash and olive. Oleander isolates infected all three hosts whereas those from olive caused symptoms only on olive and ash. All the cultures were able to multiply in host plant tissues, but the growth rates and final population densities were correlated to the plant species inoculated and the host origin of the isolates. In particular, the highest population densities were reached by isolates capable of causing symptoms on the inoculated host. The phytohormone production shown by ash, olive and oleander isolates of P. syringae ssp. savastanoi was in accordance with the type of symptoms: cankers accompanied by wart-like excrescences on ash and knots on olive and oleander. Furthermore, the pathogenic features of these isolates and, in particular, their growth patterns in the different host tissues, support previous evidence on the existence of three distinct pathovars in P. syringae ssp. savastanoi
Use of Speckle Interferometry and Modal Assurance Criterion for Identification of Component Modes
No full textOne of the problems encountered in performing modal analysis is the identification of different modes occurring at close natural frequencies. In this paper it is proposed to face such problem by an original application of the Modal Assurance Criterion, that is typically used to verify the reliability of numerical structural models by evaluating the correspondence between numerical and experimental mode shapes. To properly apply the Modal Assurance Criterion, experimental mode shapes must be retrieved acquiring data at a high number of experimental points suitably distributed on the surface of the structure. Using usual modal analysis techniques based point wise transducers, difficulties can be encountered to retrieve mode shapes with the required spatial resolution. To overcome such difficulties Speckle Interferometry techniques can be used. In this paper it is proposed a procedure based on the application of highly reliable Modal Assurance Criterion evaluated by time average Speckle Interferometry for recognising the modes contributing to the stationary vibration patterns. The results obtained from the modal analysis of a thin square plate have shown that the proposed procedure is capable to point out the component modes
Modal Tests on the Full-scale Model of a Microsatellite
No full textMicrosatellites are suitable to undergo modal test.? by Time Average Holographic Interferometry due to their small dimensions and weight. This technique has been used to detect modal shapes of the small spacecraft both in the free-free condition, and in the constrained configuration expected at the launch. Nodal lines occurring at natural frequencies are visualized as bright interferometric fringes appearing over the holographic image of the structure. Stationary vibrations occurring on the whole surface are detected adopting a holographic optical setup with a thermoplastic holographic camera. The experimental modal patterns obtained on the full-scale model, both by the holographic interferometry and the broad band technique have been used to validate the numerical model for predicting the dynamic behavior of the satellite under development
Global temperature measurements of aluminum alloy specimens with embedded optical fibers
No full textSeveral types of sensors based on optical fiber technology are available today. They can be classified into two wide categories: sensors for local and global measurements. The first ones are more expensive since they imply further processing of the optical fiber while the second one uses it directly as provided by the manufacturer. The disadvantage is that only the value of the physical quantities integrated over the fiber length can be retrieved. This is not a limitation for the present research because the main purpose of this work is to show that the process of embedding into metallic materials does not damage the optical fiber properties thus opening the way for further studies on other fiber optic sensors such as the Fiber Bragg Gratings. In the paper will be presented two different technologies for integrating the optical fibers into Aluminum alloys for aerospace use. One, tested only qualitatively in an earlier work, have been used here to build specimens with embedded optical fiber to be used as one arm of a Michelson interferometer. The results, relevant to temperature measurement. are quite satisfactory. The second one, still under development but more adequate to actual space and mechanical applications will be briefly considered
- …
