Thesis (Ph. D.)--Oregon State University, 2006. / Printout. Includes bibliographical references (leaves 405-411). Also available on the World Wide Web.

Thesis (Ph. D.)--Ohio State University, 2005. / Title from first page of PDF file. Document formatted into pages; contains xviii, 212 p.; also includes graphics (some col.). Includes bibliographical references (p. 202-212). Available online via OhioLINK's ETD Center

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1981. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / by David Matthew DeLonga; Ensign, USN. / M.S.

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science; and, (B.S.)--Massachusetts Institute of Technology, Dept. of Biology, 1978. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / B.S.

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).

Thesis (Ph. D.)--Auburn University. / Abstract. Vita. Includes bibliographical references (p. 202-209).

Drying is one of the most critical process steps in converting trees to a marketable material for use in high value wood products. The primary reasons for drying wood are to prevent biological deterioration and to improve mechanical strength and dimensional stability. The purpose of this research study was to develop an approach to the control of drying red oak lumber that monitors acoustic emission as the basis for setting environmental conditions throughout the drying process. Northern red oak (Quercus sp.) was chosen for this study because it is one of the more difficult woods grown in the United States to dry without inducing defects. This study was limited to end drying of short lengths of full sized red oak lumber. / Ph. D.

As a nondestructive examination, the acoustic emission technique is used to detect the presence of discontinuities inside of pressurized components. However, doubts still exist concerning the loading procedure to accomplish the acoustic emission testing, especially, in a pressure vessel where a uniform pressure can produce a nonuniform stress distribution due to the presence of the singularities such as the nozzles and supports. The combined loading of vapor and hydrostatic pressure can also generate a nonuniform stress distribution throughout the pressure vessel. According to the Kaiser effect, a structure with a nonuniform stress distribution should have a different acoustic emission testing result when compared to a structure with a uniform stress distribution. In this present study, the necessity to perform a stress analysis prior to the acoustic emission testing is examined. Furthermore, for the purpose of the stress analysis, two approaches are discussed, the membrane stress analysis and the finite element approach. By means of the membrane stress analysis, it is shown that the combined loading of the hydrostatic and vapor pressure does not produce a significant variation of stress throughout the spherical vessel. Actually, a computer program based on the membrane stress analysis is written to determine the stress distribution due to the combined loading. The limitation of the membrane stress analysis to handle problem with the presence of bending stress is also indicated. The finite element approach is used to perform the stress analysis of the singularities where the bending stress is important. The finite element computer program ABAQUS is used to perform the finite element stress analysis, and the mechanical computer-aided engineering program PATRAN is also used to construct the finite element model and to interpret the stress analysis results. The convenience and the success of these computer programs to handle this kind of problem are confirmed. The application of different types of finite elements to perform the stress analysis is also discussed. Results from the experiments performed by Gill, Catching and Paine [9] to measure the stress distribution of a pad reinforced nozzle is used as a benchmark to determine the performance of these finite elements. As a consequence, concrete recommendations concerning the selections of the finite elements and the stress analysis procedure are given. Finally, the influence of the stress distribution throughout the spherical pressure vessel on the acoustic emission is discussed, and the actual interpretation of the acoustic emission testing results based on the level of activity of acoustic emission without considering the nonuniform stress distribution throughout the structure is questioned. / Master of Science

Research effort was directed towards developing a near real-time, acousto-ultrasonic (AU), nondestructive evaluation (NDE) tool to study the failure mechanisms of ceramic composites. Progression of damage is monitored in real-time by observing the changes in the received AU signal during the actual test. During the real-time AU test, the AU signals are generated and received by the AU transducers attached to the specimen while it is being subjected to increasing quasi-static loads or cyclic loads (10 Hz, R = 0.1). The received AU signals for 64 successive pulses were gated in the time domain (T = 40.96 µsec) and then averaged every second over ten load cycles and stored in a computer file during fatigue tests. These averaged gated signals are representative of the damage state of the specimen at that point of its fatigue life. This is also the first major attempt in the development and application of real-time AU for continuously monitoring damage accumulation during fatigue without interrupting the test. The present work has verified the capability of the AU technique to assess the damage state in silicon carbide/calcium aluminosilicate (SiC/CAS) and silicon carbide/magnesium aluminosilicate (SiC/MAS) ceramic composites. Continuous monitoring of damage initiation and progression under quasi-static ramp loading in tension to failure of unidirectional and cross-ply SiC/CAS and quasi-isotropic SiC/MAS ceramic composite specimens at room temperature was accomplished using near real-time AU parameters. The AU technique was shown to be able to detect the stress levels for the onset and saturation of matrix cracks, respectively. The critical cracking stress level is used as a design stress for brittle matrix composites operating at elevated temperatures. The AU technique has found that the critical cracking stress level is 10-15 % below the level presently obtained for design purposes from analytical models. An acousto-ultrasonic stress-strain response (AUSSR) model for unidirectional and cross-ply ceramic composites was formulated. The AUSSR model predicts the strain response to increasing stress levels using real-time AU data and classical laminated plate theory. The Weibull parameters of the AUSSR model are used to calculate the design stress for thermo-structural applications. Real-time AU together with the AUSSR model was used to study the failure mechanisms of SiC/CAS ceramic composites under static and fatigue loading. An S-N curve was generated for a cross-ply SiC/CAS ceramic composite material. The AU results are corroborated and complemented by other NDE techniques, namely, in-situ optical microscope video recordings and edge replication. / Ph. D.

[Truncated abstract] Centrifugal pumps are the most prevalent, electrically powered rotating machines used today. Each pump is designed to deliver fluid of a given flow rate at a certain pressure. The point at which electrical energy is converted most efficiently into increased pressure is known as the Best Efficiency Point. For a variety of reasons, pumps often operate away from this point (intentionally or otherwise), which not only reduces efficiency, but also increases the likelihood of premature component failure. Acoustic emissions (AE) are high frequency elastic waves, in the range of 20-2000kHz, released when a material undergoes localised plastic deformation. Acoustic emission testing is the process of measuring and analysing these stress waves in an attempt to diagnose the nature and severity of the underlying fault. AE sensors mounted on the surface of a machine or structure also detect any stress waves generated within the fluid being transmitted through to the structure. Unfortunately, attempts to detect incipient component faults in centrifugal pumps using acoustic emission analysis have been complicated by the sensitivity of AE to a pump?s operating state. Therefore, the aim of this thesis was to determine how acoustic emission monitoring could be used to identify the hydraulic conditions within a pump. Data was collected during performance tests from a variety of small end-suction pumps and from one much larger double-suction pump. A system was developed to collect, process and analyse any number of AE features (be they related to discrete AE events, or due to the continuous background AE level) from continuously operating equipment. ... Unfortunately, results from smaller pumps were less conclusive, particularly at low flows, probably due to the relatively small changes in hydraulic energy across the range of flows, and consequent sensitivity to the testing process. However, even in these pumps consistent patterns in hit energies were observed resulting in the conclusion that low to medium flows in centrifugal pumps are typified by a very large number of very low energy (VLE) events. These decrease in number and increase in energy as flow approaches BEP and/or is reduced to very low flows. High flows above BEP are marked by an absence of these VLE events, with bursts having significantly higher energies and spread over a much greater range. Unfortunately, these VLE events are too small to affect averaged trends, indicating that further work on a suitable filter is required. vi