Thesis (M.S. in material science)--Washington State University, December 2005. / Includes bibliographical references.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1959. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves [142]-144).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1983. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 188-190).

Thesis (Ph. D.)--Virginia Commonwealth University, 2009. / Prepared for: Dept. of Anatomy and Neurobiology Title from title-page of electronic thesis. Bibliography: leaves 159-182.

In this research, Acoustography Nondestructive Evaluation method was investigated for inspecting “tight radii” in carbon fiber reinforced polymer (CFRP) components. Ultrasonic inspection of tight radii is challenging because of refraction and/or mode conversion of ultrasound waves at the entry and exiting surfaces of the tight radii. Snell’s law was used to first study the refraction and/or mode conversion behavior of the ultrasound beam at the entry and exiting surfaces of a CFRP panel; to help establish the angular range over which ultrasound is transmitted through CFRP material. Snell’s law data was then used as a guide for setting up the Acoustography system and part orientation to optimize inspection of several real-world CFRP components containing tight radii. CFRP tight-radii specimens were prepared by strategically placing markers around the tight radius of each specimen to ensure full coverage of the tight radius region. Acoustography inspection was first performed with a straight beam to establish limitation of the straight beam in detecting markers in the tight-radii region, as predicted by Snell’s law. Acoustography inspection was then performed using a multi-angle beam (+/- 12.5o) to improve detection of markers in the tight-radii region. Results confirmed that straight beam (flat transducer) could not penetrate the sample at the start of the tight radius because of refraction or mode conversion effects. However, the use of multi-angle beam (multi-angle transducer) greatly improved the penetration through the tight radius because some of beam angles were within the ultrasound transmission range for the tight radii. Experiments were also performed by changing orientation of the CFRP sample under the multi-angle or straight beam. Sample orientation was changed at five-degree increments so that optimum conditions for the tight-radii inspection could be determined. This research provides a basis on which further improvements can be made to advance the Acoustography NDE method for the inspection of tight radii in CFRP components.

Thesis (MTech (Electrical Engineering))--Cape Peninsula University of Technology, 2009 / This thesis presents the design and development of a multicell inverter for ultrasonic plastic welding applications and other ultrasonic applications. An overview of the main multilevel topologies is given, but this research focuses on the multicelll inverter, because of its capacitor voltage balancing properties. Loading effects of various plastic materials to an ultrasonic plastic welding tool are provided in this thesis. A simple method to create an approximate electrical equivalent circuit of the ultrasonic welding tool, using an impedance analyser, loaded with different plastics is discussed and illustrated. Experimental results of the four-level multicell inverter driving a resistive load and an ultrasonic transducer tool are presented in this thesis. These results provide proof that the multicell inverter topology is capable of driving a non-linear load. The inverter was tested with the ultrasonic load as an ultrasonic plastic welder and an ultrasonic drill. The welding joints on the plastic samples are also evaluated in order to evaluate whether or not this solution is suitable for plastic welding. The ultrasonic drilling results are also shown in this thesis. It is further illustrated that the ultrasonic tool and power supply combination may be used in other ultrasonic applications.

A testing method was to he developed based on previous experience on computer tomography. It has been known for some time that an image of a cross-section of an object could be reconstructed using projections or scans at different angles describing 180 degrees around the cross-section. Sound velocity, attenuation and sound reflection are the parameters used in ultrasonic computerised-tomography. The object under investigation in this work is a cylinder of acoustic properties like plastic enclosed in a steel casing. The task was to find defects in the cylinder and these defects were of a nature such, that echoes received from them are low and therefore the pulse echo technique cannot be used in their detection. A reconstruction method, based on the "Algebraic Reconstruction Techniques" (ART) is used here to detect these defects. The main achievements are that these recionstructions are obtained from constrained-scans, due to total reflection of ultrasound near the edge of the field, and a technique of obtaining an image with no background speckles. square An extensive computer simulation was done using a mathematical model of the object, which generated scan data similar to that obtained by actual experiment. Different processing techniques were tried to improve the image quality and testing reliability especially to remove the above mentioned problems. A successful method was chosen such that it will be easy to implement in a real testing situation. Successive marking of defect-free areas of the different scans resulted in a well defined defect structure. No-scan areas were identified by experiment and both the no-scan areas due to total reflection and those due to different modes of propagation received the same treatment. Using a marking technique together with the known coordinates of these areas an integrated image was obtained. The implementation of the system was done using a microcomputer together with a commercial flaw detector. The flaw detector was coupled to a digital counter to measure the transit time. The datawere acquired by interfacing the counter to the microcomputer. Data acquisition, control and processing together with the reconstruction programme constituted the software which was developed for this system.

The study was aimed at controlling the weld geometry of thin-plate titanium and one of its alloys (Ti-6Al-4V) by ultrasonic means and qualiFying the metals in the as-welded condition in terms of their grain sizes and mechanical properties. The alignment and symmetry of the weld pools were successfully tested by using ultrasonic shear waves. The grain sizes at the weld fusion zone were found to be related to their ultrasonic attenuation by a mathematical relationship. The temperature effect in locating weld pool radii in titanium was found at temperatures up to 600 °C. The ultrasonic velocity decreased as the temperature increased and the square of temperature affected the rate of change of the ultrasonic velocity. After compensation for the temperature effect, the maximum location error of the weld pool radius was 17 % which was comparable to previous measurement using different techniques.A positive relationship was seen between weld geometry (penetration depth and weld width) and heat input. A welding spectrum for titanium and its alloys of different thicknesses was obtained. Back shielding gas was beneficial in obtaining good welds. Both heat input rate and cooling rate were found to affect the grain size of the weld, with the cooling rate being the dominant factor. The grain size exhibited a Hall-Petch effect on mechanical properties, such as the tensile properties and fracture toughness of the weld. The phase transformation positively contributed to better mechanical properties in most cases, whilst the presence of interstitials worsened tensile properties. A system was developed in this study to utilise the above information and data for possible real-time and closed-loop control of the TIG welding process to give a desirable weld. Specifically, a process control data base was built up using software and a knowledge-based system for acceptable welding parameters, which were determined by acceptable penetration depth, grain size and mechanical properties. An algorithm was successfully written which relates the ultrasonic signal to the penetration depth of the weld. A hardware control circuit was built which took in the ultrasonic signal and converted it to a driving signal to change the welding speed and thereby change cooling rate.

An experimental investigation of the velocity of sound in liquid helium at temperatures near 1° K was abandoned (at an early stage)^when the results of Whitney and Chase(16) became available. The original investigation, which had been motivated by the idea that the peak in the attenuation-temperature curve near 1° K is related to a corresponding feature in the velocity-temperature curve, evolved into a search for mathematical relations connecting the temperature variations of velocity and attenuation. Classical dispersion theory is reviewed, with emphasis on its physical and mathematical foundations. Applications of the theory in the fields of electrical network design, dielectric dispersion and ultrasonics are described in order to illustrate the use and the limitations of the Kramers-Kronig relations. The possibility of extending the scope of the Kramers-Kronig relations, by using variables other than frequency, is discussed. A brief sketch of the quantum mechanical basis of linear response theory is given in support of a proposal to use reciprocal temperature as a variable in dispersion-type relations. An attempt was made to apply dispersion relations in reciprocal temperature to the problem of ultrasonic propagation in liquid helium and a comparison of the predicted and the experimentally observed attenuations at the λ point was found to give encouraging results. The interferometer, to have been used in the proposed experiment is described. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Existing methods of joining automotive aluminium alloys are either expensive (Self Pierce Rivets) or di cult to implement (Resistance Spot Welding). Ultrasonic spot welding (USW) is a new alternative method using ~2% of the energy of resistance spot welding. USW is a solid state welding process that combines vibration and pressure at the interface of a joint to produce a weld. Much of the existing research focuses testing under laboratory conditions, using simple coupon sample geometry, and has proven to be an extremely robust process. This thesis shows a detailed investigation into the implementation of USW on automotive body panels, in collaboration with Jaguar Land Rover. Weld performance, bonding mechanisms and temperature gradients found in AA5754 align well with other research conducted using 6XXX series aluminium alloys. A laboratory trial was completed to verify all joints could be achieved on a Jaguar XJ dash panel, followed by installation of a USW machine in a production cell. A detailed statistical analysis was performed on strength and sticking data gathered from 60 Jaguar XJ dash panels that were welded in the trial. Results showed difficulty to apply USW in certain areas of the panel, although previous trials had suggested it was possible. A collaboration with Ford Motor Company allowed research to be conducted at the Ford Research and Innovation Center. Experiments were designed to discover which elements of the USW equipment had the most profound effect on weld strength, and a full factorial Design of Experiments was produced to and the most effective method of reducing variation in weld strength. Results showed that the vibrational response of complex geometry parts makes USW very difficult to predict, making it difficult to successfully implement in the automotive industry.