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.

On Site Inspection is the final measure for verifying compliance of Member States with the Comprehensive Nuclear-Test-Ban Treaty. In order to enable the use of ³⁷Ar as a radiotracer for On Site Inspection, the sources of radioargon background must be characterized and quantified. A radiation transport model of the University of Texas at Austin Nuclear Engineering Teaching Laboratory (NETL) TRIGA reactor was developed to simulate the neutron flux in various regions of the reactor. An activation and depletion code was written to calculate production of ³⁷Ar in the facility based on the results of the radiation transport model. Results showed ³⁷Ar production rates of (6.567±0.31)×10² Bq·kWh⁻¹ in the re- actor pool and the air-filled irradiation facilities, and (5.811±0.40)×10⁴ Bq·kWh⁻¹ in the biological shield. Although ⁴⁰Ca activation in the biological shield was found to dominate the total radioargon inventory, the contribution to the effluent release rate would be diminished by the immobility of Ar generated in the concrete matrix and the long diffusion path of mobile radioargon. Diffusion of radioargon out of the reactor pool was found to limit the release rate but would not significantly affect the integrated release activity. The integrated ³⁷Ar release for an 8 hour operation at 950 kW was calculated to be (1.05±0.8)×10⁷ Bq, with pool emissions continuing for days and biological shield emissions continuing for tens of days following the operation. Sensitivity analyses showed that estimates for the time-dependent concentrations of ³⁷Ar in the NETL TRIGA could be made with the calculated buildup coefficients or through analytical solution of the activation equations for only (n,[gamma]) reactions in stable argon or (n,[alpha]) reactions in ⁴⁰Ca. Analyses also indicated that, for a generalized system, the integrated thermal flux can be used to calculate the buildup due to air activation and the integrated fast flux can be used to calculate the buildup due to calcium activation. Based on the results of the NETL TRIGA, an estimate of the global research reactor source term for ³⁷Ar and an estimate of ground-level ³⁷Ar concentrations near a facility were produced. / text

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

Non-destructive testing (NDT) plays an important role today in condition assessment of civil infrastructure. Among these NDT methods, the Impact-Echo (IE) method is widely used to determine the thickness of a plate structure and locate delaminations in concrete. The conventional IE test uses a contact impact source and a contact sensor, which limits the scanning speed. Recent studies show the feasibility of applying the air-coupled sensing technology to the IE test. With the contact requirement eliminated, a fully air-coupled NDT system can be realized to achieve rapid scanning on large scale structures. In this dissertation, the air-coupled IE test is first simulated using 2D finite element models. The numerical simulation results are validated by experimental measurements. It is shown that the airborne IE mode is a quasi-plane wave in air. A parabolic reflector is proposed to focus the airborne IE wave and amplify the air-coupled IE test signals. The focusing effect is validated by experimental results. By applying a parabolic reflector to the air-coupled sensor, it is found that large sensor lift-off height and source-receiver spacing can be used in the air-coupled IE test. The geometry of the parabolic reflector and source-receiver spacing are optimized using numerical simulations. A focused spark source is proposed as a non-contact source for the fully air-coupled test system. The spark source is first calibrated in an anechoic chamber. The feasibility of using the focused spark source for stress wave excitation is validated by experiments. A fully air-coupled testing system is realized by combining the air-coupled sensor and the air-coupled source. Experimental studies show that this system can measure surface wave and the IE mode. The fully air-coupled system is tested using a conventional IE test setup and a through transmission test setup. An acoustic muffler is introduced to suppress the acoustic noise from the spark source. Several advanced signal processing techniques to reduce the acoustic noises are also investigated. The air-coupled sensor has been adopted on a crawler NDT system for concrete inspection in a noisy field environment. / text

A system for the publication of the control results on food businesses were introduced in Sweden but for various reasons it was never fully implemented. It was, however, a few municipalities in Sweden which became curious about this system and gradually began to use it. In this study, I have investigated what perceptions and views local authorities and associated food businesses that use the system have and if they think that it is a good system. 2 municipalities were interviewed with related food industries and a simple questionnaire about their views on the system was sent to a few more establishments. The results showed that local authorities were satisfied with the system and considered that so far there were no disadvantages to the system. The food businesses felt that the Smiley system was mainly a positive system, and in their view above all for the customer. The non-premier a Smiley considered it a positive system so long as it was done in the right way. The majority of the interviewed businesses felt that there was a marketing value in having the Smiley sticker. / Ett system för offentliggörande av kontrollresultat på livsmedelsverksamheter i Sverige planerades för några år sedan men av olika skäl infördes aldrig systemet. Det var dock några kommuner i Sverige som på frivillig väg började använda sig av systemet. I denna studie ville jag undersöka vad inspektörerna och tillhörande livsmedelsverksamhetsutövare, som använder sig av systemet, hade för uppfattning och synpunkter på systemet benämnt Smiley. Undersökning genomfördes dels med intervjuer och dels med enkäter. Inspektörer och livsmedelsverksamhetsutövare intervjuades i två kommuner i Skåne. En enkel enkät skickades ut till några fler verksamhetsutövare i kommunen. Resultatet visade att inspektörerna var nöjda med systemet och de ansåg att det än så länge inte fanns några större nackdelar med systemet. Livsmedelsverksamhetsutövarna ansåg att i grunden är Smiley ett positivt system och framförallt ansåg de att Smiley är bra för kunden. Vid de verksamheter som inte premierats med en Smiley ansåg verksamhetsutövarna att det var ett positivt system så länge det gjordes på rätt sätt. Majoriteten av de intervjuade verksamhetsutövarna ansåg att det fanns ett marknadsföringsvärde att ha Smiley-dekalen.

published_or_final_version / Electrical and Electronic Engineering / Master / Master of Philosophy

Current metrology methods involve technicians viewing through a microscope, increasing the time, cost, and error rate in inspection. Developing an automated inspection system eliminates these difficulties. Shown in this work is a laser scanning microscope (LSM) design for an opto-electronic detection system (OEDS), based upon the concept that intensity differences related to pattern defects can be obtained from reflections off fused silica samples coated with photoresist (PR) or Aluminum. Development of this system for data collection and processing is discussed. Results show that 2.1 μm resolution of these defects is obtainable. Preliminary results for larger-array patterns through stitching processes are also shown. The second part of this work uses the concept of phase contrast edge detection. Looking at non-metallized patterns, one can use the property that phase changes induced by a refractive-index sensitive material can be seen with a multi-cell array, rendering the image visible by comparing the respective phases. A variety of defects and samples are shown. Extrapolating results to larger arrays is also discussed. Latent imaging, or imaging without development, is also evaluated. Future work in the areas of system commercialization, sample storage, and other mass-printing techniques are discussed.

The proposed study explores the feasibility of detecting and quantifying corrosion and delamination (physical separation) at the interface between reinforcing steel bars and concrete using ultrasonic guided waves. The problem of corrosion of the reinforcing steel in structures has increased significantly in recent years. The emergence of this type of concrete deterioration, which was first observed in marine structures and chemical manufacturing plants, coincided with the increased applications of deicing salts (sodium and calcium chlorides) to roads and bridges during winter months in those states where ice and snow are of major concern. Concrete is strengthened by the inclusion of the reinforcement steel such as deformed or corrugated steel bars. Bonding between the two materials plays a vital role in maximizing performance capacity of the structural members. Durability of the structure is of concern when it is exposed to aggressive environments. Corrosion of reinforcing steel has led to premature deterioration of many concrete members before their design life is attained. It is therefore, important to be able to detect and measure the level of corrosion in reinforcing steel or delamination at the interface. The development and implementation of damage detection strategies, and the continuous health assessment of concrete structures then become a matter of utmost importance. The ultimate goal of this research is to develop a nondestructive testing technique to quantify the amount of corrosion in the reinforcing steel. The guided mechanical wave approach has been explored towards the development of such methodology. The use of an embedded ultrasonic network for monitoring corrosion in real structures is feasible due to its simplicity. The ultrasonic waves, specifically cylindrical guided waves can propagate a long distance along the reinforcing steel bars and are found to be sensitive to the interface conditions between steel bars and concrete. Ultrasonic transducers are used to launch and detect cylindrical guided waves along the steel bar.In this dissertation, in-situ corrosion monitoring technique for reinforced concrete is developed based on two methods - 1) variation of signal strength and 2) the time-of-flight (TOF) variations as the corroded member is loaded transversely. This is the first attempt ever to monitor corrosion inside concrete by measuring the change in the time of flight of guided waves along reinforcing bars as the concrete beam is subjected to bending. Advantages of corrosion monitoring by TOF change are discussed in the dissertation.

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