Adhesives have presently reached a stage where they have become part of everyday life both in a professional sense as well as for household applications. They offer advantages that in many respects surpass other joining processes such as bonding of large areas, joining a wide range and dissimilar materials; and without the need for special tooling or operator training, that is often required by many other joining processes. They are of course not a panacea to all fastening applications, but they can easily be described as the most versatile and most widely used joining method at present. Engineering applications have also benefited from the advantages offered by adhesives, but they are not as liberally used due to the severe consequences that may result from bond failure. Although adhesives can demonstrate their ability to fulfil the joining strength requirements under laboratory conditions, their application in industry proved to be not as reliable as expected. A number of parameters that can easily be controlled under laboratory conditions such as temperature, humidity, surface preparation and uniform adhesive application are not as easily observed in industry. Quality assurance during manufacturing can achieve excellent results; however even in these cases the probability of having adhesive bond defects is still present. Therefore, there is a need for post process inspection of adhesive bonds where risk levels require higher reliability than what is offered though process quality control. Adhesive bond inspection is a well researched area with respectable outcomes. Non destructive inspection techniques such as x-ray, thermal, and ultrasonic are well utilised in the inspection of adhesive bonds. However, despite all the effort in this area for more than forty years, there is still no singular technique that can achieve the confidence level required in some engineering applications. Therefore, the need for continuing research in the area of non-destructive evaluation of adhesive bonds is as necessary today as it�s ever been. The research presented in this thesis, continues in the same endeavour as many other researchers; that of achieving the ultimate technique in adhesive bond inspection, capable of reaching the confidence level required for all engineering applications. The research in the thesis commenced with coverage of adhesives used for engineering applications and a study of the adhesion science that was considered necessary to enable an informed approach to the problem. Adhesive bond failure is also analysed through a literature survey as well as experimental tests on standard specimens. At the completion of the literature survey and preliminary tests, a decision was taken to follow the ultrasonic path of non-destructive testing of adhesive bonds. The reasons for this, are clearly outlined in the main body of this thesis but in summary, the literature has shown that ultrasonic evaluation is the most widely used technique by industry. Therefore, improvements on data analysis using existing techniques that exploit ultrasonic inspection have the potential to reach the widest spectrum of industrial applications. Ultrasonic inspection equipment was sourced that was capable of achieving experimental results to the accuracy level required in this research. A precision test rig was designed and constructed that was subsequently calibrated using computer based statistical techniques to ensure the validity of all results. Other ancillary equipment, such as a portable tensile testing device were also designed and constructed during the research as it became necessary. Research concentrated on techniques found to be inadequately researched in this domain. The first technique evaluated was to measure bond quality through the stress distribution in adherent and adhesive. Computer based Finite Element Analysis showed that the ability to detect variation in stress distribution at the adhesion interface is capable of revealing the local bond strength. Having found that there is no technique available at present that can measure the stress distribution at the interface, a different direction was taken that showed potential in achieving excellent quantitative results in the analysis of ultrasonic signals from adhesive bonds. This technique was rigorously evaluated and the results are systematically reported in this work.

Thesis (Ph. D. in Civil Engineering)--Vanderbilt University, May 2007. / Title from title screen. Includes bibliographical references.

This thesis evaluates a particular ultrasonic nondestructive testing (NDT) system in order to determine its capabilities and limitations in locating defects in concrete structures; specifically tunnel linings, bridge decks, and pavements. The device, a phased-array ultrasonic tomography (UST) system that utilizes shear waves, is a significant advancement in NDT systems. Consequently, there is a need in structural engineering to verify new technologies by assessing their flaw-detecting capabilities in a variety of structural applications. The UST technique does not currently have a testing methodology that is field-ready. In order to develop a methodology, the system was evaluated based on its ability to detect simulated defects, then taken to the field to evaluate natural structural defects on public tunnels, pavements, and airport runways. Types of concrete defects the system is used to detect and localize include air- and water-filled voids, vertical cracks, horizontal delaminations, and abnormalities such as clay lumps. The device is also used to determine reinforcement depth and spacing as well as concrete thickness measurements. This research concludes that the UST system is exceptional at locating horizontal delaminations ranging from 0.05-2.0 mm (0.002-0.079 in.), and is able to differentiate between fully debonded and partially-bonded areas. Vertical cracks could only be detected once they begin to form parallel to the testing surface; however, omission of surface details was found to be a strong indicator of crack presence. Backwall surfaces up to a depth of 762 mm (30 in.) were successfully and accurately determined. Air- and water-filled voids as well as reinforcement details such as layout and depth were also successfully determined and located. With the exception of some medium-sized clay lumps (with a diameter of approximately 102 mm, or 4 in.) surrounding reinforcement, all clay lumps tested were also highly successful.

Thesis (M.S.)--University of Missouri-Columbia, 2003. / Typescript. Includes bibliographical references (leaves 99-101). Also available on the Internet.

Thesis (M.S.)--University of Missouri-Columbia, 2003. / Typescript. Includes bibliographical references (leaves 99-101). Also available on the Internet.

Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Ume, I. Charles; Committee Member: Kalaitzidou, Kyriaki; Committee Member: Mayor, J. Rhett. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Identifying damage of a bridge from a vehicle moving over it is an attractive idea especially for those bridges without structural health monitoring systems as it is faster than putting sensors on the bridges. Many parts of highways and railways have been constructed on bridges and it is important to ensure that they are in good conditions. Therefore a large amount of bridges need to be monitored and for the sake of economy the monitoring should be efficient. If an instrumented vehicle can identify the occurrence and locations of damage by running over the bridges, it would save a lot of labor and time. As acceleration is easier to acquire, it is used as the main signal for damage detection. Research in this area is relatively little, not to mention the need to take into account road surface roughness and experimental verification. Frequencies can be conveniently extracted from the vehicle response. The damage can hence be identified based on the relationship between the change of frequencies and the fractional change of strain energy. A vehicle-bridge interaction system is used to simulate the process of a vehicle running over a bridge and obtain the vehicle response for investigation. The proposed method can identify damage of simply supported and multi-span continuous bridges taking into account road surface roughness and measurement noise. They are also validated in the laboratory where a simply supported bridge is modeled using an aluminum beam and the vehicle is modeled with aluminum vehicles. This method can limit the damage location to two potential locations. The multi-level multi-pass strategy makes use of the identification from the above method, applies genetic algorithm and lets the vehicle run over the bridge at various speeds. The unique damage location can then be identified. A numerical study for simply supported bridges and multi-span continuous bridges has verified its effectiveness. Continuous wavelet transform (CWT) can identify local changes in a signal as damage is assumed to cause local change to the vehicle response, which makes it suitable for damage detection from vehicle response. However, the road surface roughness and measurement noise often mask the information about damage. Smoothing technique and damage indicators are proposed to help with the identification. By validating the method with a numerical vehicle-bridge interaction system and model tests in the laboratory, the damage can be correctly identified. Additional masses and sinusoidal excitation force can help with the identification too. Repeated application of CWT involves applying the CWT to the coefficients of continuous wavelet again and again, which can also improve the results. If CWT is treated as a mathematical microscope, repeated application of CWT is like amplifying the signal several times. The effectiveness of the method has been verified numerically and experimentally. In summary, a convenient and efficient technique to test the conditions of bridges by putting sensors on a moving vehicle is proposed and the method is verified by numerical and experimental studies. It can provide an alternative or a useful complement to conventional structural health monitoring systems. / published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

Thesis (MTech. : Engineering Metallurgy.)--Tshwane University of Technology, 2010. / Establish a qualitative and quantitative comparison between the parameters of the laser used in manufacturing a 120 mm curvature in HSLA steel parts and the micro-structural changes in the steel part. Subsequently, the final microstructure will be used to determine the reason for the poor fatigue performance of the HSLA steel after laser forming.

published_or_final_version / Electrical Engineering / Master / Master of Philosophy

published_or_final_version / Electrical Engineering / Doctoral / Doctor of Philosophy