No description available.

Slow speed rotating machines are the mainstay of several industrial applications worldwide. They can be found in paper and steel mills, rotating biological contractors, wind turbines etc. Operational experience of such machinery has not only revealed the early design problems but has also presented opportunities for further significant improvements in the technology and economics of the machines. Slow speed rotating machinery maintenance, mostly related to bearings, shafts and gearbox problems, represents the cause of extended outages. Rotating machinery components such as gearboxes, shafts and bearings degrade slowly with operating time. Such a slow degradation process can be identified if a robust on-line monitoring and predictive maintenance technology is used to detect impending problems and allow repairs to be scheduled. To keep machines functioning at optimal levels, failure detection of such vital components is important as any mechanical degradation or wear, if is not impeded in time, will often progress to more serious damage affecting the operational performance of the machine. This requires far more costly repairs than simply replacing a part. Over the last few years there have been many developments in the use of Acoustic Emission (AE) technology and its analysis for monitoring the condition of rotating machinery whilst in operation, particularly on slow speed rotating machinery. Unlike conventional technologies such as thermography, oil analysis, strain measurements and vibration, AE has been introduced due to its increased sensitivity in detecting the earliest stages of loss of mechanical integrity. This programme of research involves laboratory tests for monitoring slow speed rotating machinery components (shafts and bearings) using AE technology. To implement this objective, two test rigs have been designed to assess the capability of AE as an effective tool for detection of incipient defects within low speed machine components (e.g. shafts and bearings). The focus of the experimental work will be on the initiation and growth of natural defects. Further, this research work investigates the source characterizations of AE signals associated with such bearings whilst in operation. It is also hoped that at the end of this research program, a reliable on-line monitoring scheme used for slow speed rotating machinery components can be developed.

The goal of this thesis is to experimentally characterize the flyability of current generation read/write heads over media patterned to densities above the superparamagnetic limit. The superparamagnetic limit is the physical limit to magnetic storage density. In magnetic storage, superparamagnetism is the uncontrollable switching of stored bits during the lifespan of a hard disk. Theoretical analysis has predicted that densities of ~50 Gbit/in2 are not possible using traditional continuous media. One strategy to achieve high storage density, above the superparamagnetic limit, is patterned media. With patterned media the physical separation of magnetic domains increases their stability. One of the major challenges of development of patterned media is achieving acceptable flyability of the read/write head. In that vein, a test stand is built to measure head liftoff speed, head to disk intermittent contact and head fly height. Tangential friction, an indicator of head liftoff is measured by a Wheatstone bridge strain circuit attached to a cantilever beam. Intermittent contact is quantified by the amount of noise emanating from the interface, which is measured by a high frequency acoustic emission sensor. Head fly height is measured indirectly with a capacitance circuit built around the head to disk interface. Experimental samples of current generation read/write heads and media are obtained from industry. Current generation media is patterned using focused ion beam milling to a density of 10 Gbit/in2. Other, extremely dense samples, above 700 Gbit/in2, are created via thin film self assembly on silicon substrate. Conclusions on slider head flyability over patterned media are based on comparison with flyability over non-patterned media. It is demonstrated that loss of hydrodynamic lubrication is small for small pattern regions with high conserved surface area ratio. Conserved surface area ratio is defined as total surface area minus etched surface area all divided by the total surface area of the storage media. For wafer scale patterned media with low conserved surface area ratio, head liftoff cannot be achieved at designed normal load. However, a 50% reduction of load allows slider head liftoff.

Joints represent a design challenge, especially for composite structures. Among the available joining methods, co-curing is an efficient way to integrate parts for some applications. Coates and Armanios have proposed a Single Nested Overlap (SNO) co-cured joint configuration, obtained from a single lap joint through the overlap/interleafing of the adjoining top/bottom adherend plies, respectively. Through a comparative investigation, they have demonstrated joint strength and fatigue life improvements over the single lap joint counterparts for unidirectional and quasi-isotropic adherend lay-ups. This research extends the comparative investigation of Coates and Armanios by focusing upon characterizing and differentiating the damage initiation and progression mechanisms under quasi-static loading. Six specimen configurations are manufactured and tested. It is confirmed that single nested overlap joints show 29.2% and 27.4% average improvement in strength over single lap counterparts for zero-degree unidirectional and quasi-isotropic lay-ups, respectively. Several nondestructive evaluation techniques are used to observe and analyze damage initiation, damage progression and failure modes of the studied specimens and to monitor their mechanical response. Using X-ray Radiography and Optical Microscopy techniques during quasi-static loading, a physical characterization of damage and failure mechanisms is obtained. The acoustic emission data acquired during monotonic loading could reveal the overall picture of AE activities produced by the damage initiation, development and accumulation mechanisms within the specimen via parametric analysis. Further AE analysis by a selected supervised clustering method is carried out and shown successful in differentiating and clustering the AE data. Correlation with physical observations from other techniques suggests that the resulting clusters may be associated to specific damage modes and failure mechanisms.

No description available.

<p>Automobile and aero industries have an increasing interestin materials with improved mechanical properties. However, manyof these new materials are classified as difficult-to-cut withconventional tools. It is obvious that tools, cutting processesand cutting models has to be devel-oped parallel to materialsscience. In this thesis rotary cutting tools are tested as analternative toexpensive diamond or cubic bore nitridetools.</p><p>Metal matrix composites mostly consist of a light metalalloy (such as aluminium or titanium) reinforced with hard andabrasive ceramic parti-cles or fibres. On machining, thereinforcement results in a high rate of tool wear. This is themain problem for the machining of MMCs. Many factors affect thelife length of a tool, i.e. matrix alloy, type, size andfraction of the reinforcement, heat treatment, cuttingconditions and tool properties.</p><p>In tests, the Al-SiC MMC formed a deformation layer duringmilling, probably affected by lack of cooling. The dominatingfactor for tool life was the cutting speed. Water jet or CO2cooling of turning did not provide dramatic increase in toollife. With PCD, cutting speeds up to 2000 m/min were usedwithout machining problems and BUE formation. Tool flank wearwas abrasive and crater wear created an "orange-peel type" wearsurface. PCD inserts did not show the typical increase in flankwear rate at the end of its lifetime.</p><p>The use of self-propelled rotary tools seems to be apromising way to increase tool life. No BUE was formed on therotary tool at high cutting data. The measurements indicatethat the rotary tool creates twice as good surface as PCDtools. The longest tool life was gained with an inclinationangle of 10 degrees. Tool costs per component will beapproximately the same, but rotary cutting tool allows higherfeeds and therefore a higher production rate and thus a lowerproduction cost.</p><p>The rotary cutting operation might have a potential toincrease productiv-ity in bar peeling. The lack of BUE withrotary cutting gives hope on higher tool life. The test resultsshow that tool wear was 27% lower with rotary cutting tools.Increase of cutting speed from 22 to 44 m/min did not affectcutting forces. This indicates that the cutting speed canincrease without significant change in tool wear rate.</p><p>Issues related to rotary cutting like cutting models,cutting processes, standards, tools and models have beendiscussed. A tool wear model with kinetic energy has beendiscussed.</p><p><b>KEYWORDS:</b>Difficult-to-Cut material, Metal MatrixComposite (MMC), Machining, Machinability, Rotary Cutting Tool,Acoustic Emission</p>

Thesis (M.S.)--West Virginia University, 2003. / Title from document title page. Document formatted into pages; contains x, 61 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 59-61).

Ο Έλεγχος Δομικής Ακεραιότητας (ΕΔΤ) μέσω Ακουστικής Εκπομπής, αποτελεί ένα σημαντικό εργαλείο της μηχανικής στην έγκαιρη διάγνωση δομικών σφαλμάτων και στην αύξηση της διάρκειας ζωής κτηρίων. Οι σύγχρονες εφαρμογές συστημάτων ΕΔΤ χαρακτηρίζονται από μεγάλο κόστος εφαρμογής και συντήρησης. Χρησιμοποιώντας νέες τεχνολογίες ολοκληρωμένων συστημάτων χαμηλής κατανάλωσης ισχύος, ασύρματης επικοινωνίας, καθώς επίσης και τεχνικών ψηφιακής επεξεργασίας σημάτων και αναγνώρισης προτύπων, μπορεί να δημιουργηθεί ένα σύστημα ΕΔΤ φθηνό και αποδοτικό. Στόχος μας σε αυτή την διπλωματική είναι η υλοποίηση ενός συστήματος ασύρματων αισθητήρων, ικανών να επιτελέσουν έλεγχο δομικής ακεραιότητας μέσω ακουστικής εκπομπής, χρησιμοποιώντας μικροελεγκτές LPC2148 και πομποδέκτες nRF24L01. / Structural health monitoring with acoustic emission techniques is an important engineering tool in the diagnosis of structural faults. Modern applications of SHM systems are difficult to implement and cost inefficient. By using new integrated systems technologies, wireless communications, coupled with better techniques in signal processing and pattern recognition, a much more cheap and efficient SHM system may be build. Our target in this thesis, is to implement a wireless sensor system, capable of SHM with acoustic emission, by using LPC2148 microcontrollers and nRF24L01 transceivers.

Η διπλωματική εργασία ασχολείται με τον χαρακτηρισμό σημάτων ακουστικής εκπομπής και της πηγής τους μέσω της επεξεργασίας χαρακτηριστικών παραμέτρων που έχουν εξαχθεί από αυτά. Θεωρητικό υπόβαθρο της εργασίας είναι οι επιστημονικές περιοχές της Αναγνώρισης Προτύπων, Τεχνητής Νοημοσύνης και Νευρωνικών Δικτύων καθώς και η Επεξεργασία Σημάτων. Ο τομέας εφαρμογής της εργασίας είναι ο Μη Καταστροφικός Έλεγχος και η Ακουστική Εκπομπή και η ίδια αποτελεί μια τέτοια εφαρμογή. Τα δεδομένα που επεξεργάστηκαν χωρίζονται σε δύο κατηγορίες: σε εκείνα που δόθηκαν έτοιμα και σε εκείνα που προέκυψαν μετά από επεξεργασία. / This graduate project concerns the characterization of the acoustic emission of signals and their sources that have been exported through the process of characteristic parameters.The theoritical substratum of this project are scientific areas such as pattern recognition, artificial intelligence, neural network ,as well as signal processing.The sector which this project applicate is non-distractive testing and signal emission and the project itself consists such an application.The data that have been processed are divided in two categories:in this one where the data were already given and in that one where the data arised after process.

The failure of brittle rocks around deep underground excavations due to the high induced stress is controlled by the crack accumulation in the rock. The study shows that the damage initiation strength, CI, corresponds to the long-term strength, and the short-term strength of the brittle rocks in-situ is the crack interaction strength, CD. Therefore the damage thresholds that are being used for the calibration and validation of numerical models are important parameters in the design of underground structures. The accurate detection of the damage thresholds is important as they define the in-situ behaviour of the brittle rocks. The two most common methods of detecting damage thresholds are the Acoustic Emission method and the strain measurement method. Apparent discrepancy that exists between the accuracy of these methods was the author’s motivation for comparing these two methods on Stanstead and Smaland granites. The author introduced two new parameters based on the measured strains for improving the strain measurement method. Based on the comparisons, the author is of the opinion that the Acoustic Emission method is a more accurate method of detecting damage thresholds. Numerical models are an important tool in the design of underground structures. The numerical methods that are able to simulate fractures explicitly have the ability to predict the brittle failure, the density and the extension of the microcracks around the opening. Itasca’s Particle Flow Code (PFC) was used in this study due to its potential to simulate fractures explicitly. Calibration of PFC models to Unconfined Compressive Strength properties of the rock does not mean that the model will behave correctly under other confining stresses or in tension. The author has tried to solve this problem by different methods and developing new procedures. Improvements in the model behaviour have been achieved but more work is required. The definition, and detection and calibrated simulation of rock damage thresholds for calibration of numerical models is helpful for a successful design of underground excavations and long term, lower bound strength, a critical design parameter for deep geological repositories for the storage of nuclear wastes, for example. / Thesis (Master, Geological Sciences & Geological Engineering) -- Queen's University, 2010-09-23 13:59:28.795