Thesis (Ph. D.)--Lehigh University, 2005. / In two parts. Includes bibliographical references and vita.

Thesis (Ph.D.)--University of Nebraska-Lincoln, 2008. / Title from title screen (site viewed Jan. 15, 2009). PDF text: 260 p. : ill. (some col.) ; 19 Mb. UMI publication number: AAT 3315882. Includes bibliographical references. Also available in microfilm and microfiche formats.

With the increase in the application of ultra-precision manufactured parts and the absence of much participation of researchers in ultra-high precision grinding of optical glasses which has a high rate of demand in the industries, it becomes imperative to garner a full understanding of the production of these precision optics using the above-listed technology. Single point inclined axes grinding configuration and Box-Behnken experimental design was developed and applied to the ultra-high precision grinding of BK7 glass. A high sampling acoustic emission monitoring system was implemented to monitor the process. The research tends to monitor the ultra-high precision grinding of BK7 glass using acoustic emission which has proven to be an effective sensing technique to monitor grinding processes. Response surface methodology was adopted to analyze the effect of the interaction between the machining parameters: feed, speed, depth of cut and the generated surface roughness. Furthermore, back propagation Artificial Neural Network was also implemented through careful feature extraction and selection process. The proposed models are aimed at creating a database guide to the ultra-high precision grinding of precision optics.

Experience shows that the noise and sound quality in vehicles are often a recurring criticism. The bodies of modern vehicles consist predominantly of thin sheets of metal. It is hard to prevent the excitation of bending vibrations and the subsequent emission of disturbing noise while driving. The noise spectrum in a car that can be heard by the driver is from ”latent roar” to ”chattering” noise of the body and engine. In automotive vehicles damped materials, especially plastics or materials made from sheet metal and surface damping treatments, are used. Those have high internal energy losses and damp sound oscillatory systems found in the body or interior of cars. A further advantage of such treated components is that they are applied to existing components working over wide temperature and frequency ranges. Many companies provide such ”sound-absorbing compounds”. The requirements for these damping materials are high temperature-resistance, water repellence, fuel and oil-resistance and good adhesion to the base material [17]. The acoustic properties, especially the damping of the plate vibrations through rubber are of interest. the question arises how can the damping coeficient of coated metal sheets can be measured and secondly, by how much the road noise is reduced when built-in sheets are coated with a known damped material. With the Oberst Bar Test Method (named after Dr. H. Oberst) the properties are determined of the internal damping materials that can be used to simulate mechanical constructions to determine damping of larger surfaces. This method describes a laboratory test procedure for measuring the mechanical properties of damped materials. A block diagram of the test system consisting of a damped material bonded to a vibrating cantilever steel bar is shown in figure 2.1. This method is useful for testing materials such as metals, enamels, ceramics, rubbers, plastics, reinforced epoxy matrices and wood. In addition to damping measurement, the test allows for the determination of the Young’s modulus E of the material. E is calculated from the resonance frequency of a given mode and from the physical constants of the bar. By associating the damping factor with the Young’s modulus, a complex quantity is defined which is called the Complex Modulus of Elasticity. Measurements of dynamic mechanical properties are also useful in the research on the molecular structure of materials.

abstract: Acoustic emission (AE) signals have been widely employed for tracking material properties and structural characteristics. In this study, the aim is to analyze the AE signals gathered during a scanning probe lithography process to classify the known microstructure types and discover unknown surface microstructures/anomalies. To achieve this, a Hidden Markov Model is developed to consider the temporal dependency of the high-resolution AE data. Furthermore, the posterior classification probability and the negative likelihood score for microstructure classification and discovery are computed. Subsequently, a diagnostic procedure to identify the dominant AE frequencies that were used to track the microstructural characteristics is presented. In addition, machine learning methods such as KNN, Naive Bayes, and Logistic Regression classifiers are applied. Finally, the proposed approach applied to identify the surface microstructures of additively manufactured Ti-6Al-4V and show that it not only achieved a high classification accuracy (e.g., more than 90\%) but also correctly identified the microstructural anomalies that may be subjected to further investigation to discover new material phases/properties. / Dissertation/Thesis / Masters Thesis Statistics 2020

This dissertation proposes a system for weighing commercial vehicles in motion using acoustic emission sensors attached to a metal bar placed across the roadway. The signal from the sensors is analyzed by a computer and the vehicle weight is determined by a statistical model which correlates the acoustic emission parameters to the vehicle weight. Such a system would be portable and low-cost, allowing for the measurement of vehicle weights in much the same way commercial tube and radar counters routinely collect vehicle speed and count. The system could be used to collect vehicle speed and count data as well as weight information. Acoustic emissions are naturally occurring elastic waves produced by the rapid release of energy within a material. They are caused by deformation or fracturing of a solid due to thermal or mechanical stress. Acoustic emission sensors have been developed to detect these waves and computer software and hardware have been developed to analyze and provide information about the waveforms. Acoustic emission testing is a common form of nondestructive testing and is used for pressure vessel testing, leak detection, machinery monitoring, structural integrity monitoring, and weld monitoring, among other things (Miller, 1987). For this dissertation, acoustic emission parameters were correlated to the load placed on the metal test bar to determine the feasibility of using a metal test bar to measure the weight of a vehicle in motion. Several experiments were done. First, the concept was tested in a laboratory setting using an experimental apparatus. A concrete cylinder was mounted on a frame and rotated using a motor. The metal test bar was applied directly to the surface of the cylinder and iv acoustic emission sensors were attached to each end of the bar. As the cylinder rotated, a motorcycle tire was pushed up against the cylinder using a scissor jack to simulate different loads. The acoustic emission response in the metal test strip to the motorcycle tire rolling over it was detected by the acoustic emission sensors and analyzed by the computer. Initial examinations of the data showed a correlation between the force of the tire against the cylinder and the energy and count of the acoustic emissions. Subsequent field experiments were performed at a weigh station on I-95 in Flagler County, Florida. The proposed weigh-in-motion system (the metal test bar with attached acoustic emission sensors) was installed just downstream of the existing weigh-in-motion scale at the weigh station. Commercial vehicles were weighed on the weigh station weigh-in-motion scale and acoustic emission data was collected by the experimental system. Test data was collected over several hours on two different days, one in July 2008 and the other in April 2009. Initial examination of the data did not show direct correlation between any acoustic emission parameter and vehicle weight. As a result, a more sophisticated model was developed. Dimensional analysis was used to examine possible relationships between the acoustic emission parameters and the vehicle weight. In dimensional analysis, a dimensionally correct equation is formed using measurable parameters of a system. The dimensionally correct equation can then be tested using experimental data. Dimensional analysis revealed the following possible relationship between the acoustic emission parameters and the vehicle weight: ! = " # $% &2 , '(, )% *+( , ,% +( , ,-% +( , %3 +( . (/0% , 1% +( 2 v The definitions of these variables can be found in Appendix A. Statistical models for weight using the laboratory data and using the field data were developed. Dimensional analysis variables as well as other relevant measurable parameters were used in the development of the statistical models. The model created for the April 2009 dataset was validated, with only 27 lbs average error in the weight calculation as compared with the weight measurement made with the weigh station weigh-in-motion scale. The maximum percent error for the weight calculation was 204%, with about 65% of the data falling within 30% error. Additional research will be needed to develop an acoustic emission weigh-in-motion system with adequate accuracy for a commercial product. Nevertheless, this dissertation presents a valuable contribution to the effort of developing a low-cost acoustic emission weigh-in-motion scale. Future research needs that were identified as part of this dissertation include: ! Examination of the effects of pavement type (flexible or rigid), vehicle speeds greater than 50 mph, and temperature ! Determination of the best acoustic emission sensor for this system ! Exploration of the best method to separate the data from axles which pass over the equipment close together in time (such as tandem axles) ! Exploration of the effect of repeated measures on improving the accuracy of the system.

No description available.

Velocity tomography is a noninvasive technique that can image the interior of a rock structure. To apply tomography to rock specimens, a propagation wave, which acts as a probe, is used. The propagation wave propagates from a source until it reaches a sensor on the surface of the rock specimen. Tomograms can then be generated from the velocity distribution within the rock structure. Areas of higher velocity are typically representative of higher stress concentrations, whereas areas of low velocity can be areas of fracturing. The variation of velocity tomography described in this thesis uses acoustic emissions as sources for the propagation wave. Acoustic emission sources provide advantages over mechanical sources, since the acoustic emission source is generated by the rock as a result of deformation and fracturing. Velocity tomography of rock structures in the field has numerous applications and advantages. Velocity tomography can be used to monitor rock structures surrounding tunnels and underground openings such as mines. To monitor the rock structure, velocity tomography is used to determine areas of higher stress concentration that may be precursors to rock failure. However, velocity tomography must first be used in a laboratory environment to determine failure in rock samples before being applied to the field. The research presented includes the unconfined compression strength testing of 19 Berea sandstone samples. These samples were loaded to failure and during the experiment the acoustic emission events within the samples were monitored using a commercial acquisition system manufactured by Engineering Seismology Group (ESG) Canada. Source location software, also produced by ESG, was used for the location of the acoustic emission events. Ray inversions were performed on the data from the experiments to generate tomograms. The tomograms generated display the p-wave velocity distribution imaged within the Berea sandstone samples with the ultimate goal of being able to predict rock failure. Based on the experiments discussed in this thesis it can be inferred that velocity tomography is a useful tool for imaging the inside of the Berea sandstone samples. Precursors of rock failure could not be determined in this early stage of research. However, the tomograms do image the p-wave velocity distribution and do show a gradual progression of the p-wave velocity from the initial velocity model to higher velocities. Results of these 19 experiments do provide reasonable confidence in the method and warrant pursuit of further research to refine and improve this method of monitoring velocity tomography. / Master of Science

With increasing applications of composite materials, their health monitoring is of growing importance in engineering practice. Damage development in composite materials is more complex than for metallic materials, because in composite materials (a) multiple damage modes are simultaneously in play, and (b) individual 'damage events' that occur throughout a component's service life may neither noticeably affect its performance, nor suggest future failure. Therefore, informed health monitoring of composite components must include monitoring and analysis of their health state throughout their service life. A crucial aspect of the health monitoring process of composites is the development of tools to help with this goal of understanding the health state of composites throughout their life. This knowledge can lead to timely anticipation of future failure in composite components, and advance the state of current technology. One, timely maintenance can be planned in advance. Two, each component's service life can be determined based on its individual health information, rather than empirical statistics of previously failed components. This dissertation develops such tools and methods. Composite specimens of multiple ply-layups are subjected to tensile loading schemes until failure. Pencil Lead Breaks (PLBs) are used to simulate Acoustic Emission sources and generate acoustic waves that are acquired by installed piezoelectric sensors. A numerical method to estimate the arrival of wave modes from ultrasonic signals is presented. Methods are also presented that utilize PLB signals to indicate approaching failure of specimens under monotonic as well as cyclic loading. These processes have been developed prioritizing simplicity and ease-of-execution, to be adapted for practical deployment. / Ph. D.

Approved for public release, distribution is unlimited / When a burst of air is produced in water, the result can be a toroidal bubble. This thesis is concerned with experimental investigations of three acoustical properties of toroidal bubbles: (i) propagation through high-intensity noise, (ii) emission, and (iii) scattering. In (i), an attempt to observe a recent prediction of the acoustic drag on a bubble is described, which is analogous to the Einstein-Hopf effect for an oscillating electric dipole in a fluctuating electromagnetic field. No effect was observed, which may be due to insufficient amplitude of the noise. In (ii), observations of acoustic emissions of volume oscillations of toroidal bubbles are reported. Surprisingly, the emission occurs primarily during the formation of a bubble, and is weak in the case of very smooth toroidal bubbles. In (iii), we describe an experiment to observe the effect of a toroidal bubble on an incident sound field. In addition to the acoustical investigations, we describe the construction of a large hallway apparatus for further investigations and for hands-on use by the public. The tank has cross section 2 feet by 2 feet and height 6 feet, and the parameters of reservoir pressure and time between air bursts are adjustable by the observer. / Lieutenant, United States Navy