The focus of this thesis is to derive analytical tools for the design of infrared nondestructive tests in single and multi layer material bodies. This requires the predetermination of the parameters of the experiment such that the infrared image has the required resolution for defect detection. Inverse heat conduction in single and multi-layer materials is investigated to determine the required frequency of excitation in order to obtain a desired temperature at the observation point. We use analytical quadrupole representation to derive a polynomial relation to estimate the frequency of the periodic excitation as a function of the temperature amplitude at a given observation point within the body. The formula includes characteristic geometric and material parameters of the system. The polynomial formula can be an e ective design tool for quick frequency predetermination in the design of non-destructive testing experiments with infrared thermography. The convergence and accuracy of the formula is assessed by comparison with the analytical thermal quadrupole solution and experimental results. We also investigate the e ect of the nite length of the material domain in order to establish the range of applicability of a simpli ed formula based on semi-in nite domain assumption. The e ect of nite length is investigated analytically by using (i) Fourier series which accounts for transients and (ii) Time varying solution associated to the steady state solution when a purely periodic excitation is applied. These results are also compared with numerical solution obtained with commercial nite element software ANSYSTM.

Time of Flight Diffraction (TOFD) is one of the most accurate ultrasonic methods for crack detection and sizing in pipeline girth welds. Its performance, however, is limited by the temporal resolution of the signal. In this thesis, we develop a signal processing method based on autoregressive spectral extrapolation to improve the temporal resolution of ultrasonic signals. The original method cannot be used in industrial applications since its performance is highly dependent on selection of a number of free parameters. This method is modified by optimizing its various steps and limiting the number of free parameters, and an automated algorithm for selection of values for the remaining free parameters is proposed based on the analysis of a large set of synthetic signals. The performance of the final algorithm is evaluated using experimental data; it is shown that the uncertainty in crack sizing accuracy can be reduced by as much as 80%. Furthermore, the proposed method is shown to be capable of resolving overlapping echoes; therefore, smaller cracks that have echoes that are not clearly resolved in the raw signal, can be detected and sized in the enhanced signal.

Time of Flight Diffraction (TOFD) is one of the most accurate ultrasonic methods for crack detection and sizing in pipeline girth welds. Its performance, however, is limited by the temporal resolution of the signal. In this thesis, we develop a signal processing method based on autoregressive spectral extrapolation to improve the temporal resolution of ultrasonic signals. The original method cannot be used in industrial applications since its performance is highly dependent on selection of a number of free parameters. This method is modified by optimizing its various steps and limiting the number of free parameters, and an automated algorithm for selection of values for the remaining free parameters is proposed based on the analysis of a large set of synthetic signals. The performance of the final algorithm is evaluated using experimental data; it is shown that the uncertainty in crack sizing accuracy can be reduced by as much as 80%. Furthermore, the proposed method is shown to be capable of resolving overlapping echoes; therefore, smaller cracks that have echoes that are not clearly resolved in the raw signal, can be detected and sized in the enhanced signal.

In certain industries, quality testing is crucial, to make sure that the components being manufactured do not contain any defects. One method to detect these defects is to heat the specimen being inspected and then to study the cooling process using infrared thermography. The explorations of non-destructive testing using thermography is at an early stage and therefore the purpose of this thesis is to analyse some of the existing techniques and to propose improvements. A test specimen containing several different defects was designed specifically for this thesis. A flash lamp was used to heat the specimen and a high-speed infrared camera was used to study both the spatial and temporal features of the cooling process. An algorithm was implemented to detect anomalies and different parameter settings were evaluated. The results show that the proposed method is successful at finding the searched for defects, and also outperforms one of the old methods.

No description available.

In order to reach the economic scale, reduce unit cost and to enhance the international competitiveness, China Steel Cooperation constructed a subsidiary - Dragon Steel Cooperation, a 5-million-ton integrated steel plant nearby Taichung Harbor. Starting from iron-smelting, steel-making till steel-rolling, each step follows one another. If any of the steps occurs a problem, the whole production will be affected. The quality of the new construction is related to the life cycle of the equipments, the stability of the operation and the quality of the products. Further more, if the new construction is imperfect, there might be plenty of accidents, such as public safety, environment issues, protest from the inhabitants, etc. The influences could be huge. The main quality influences of the new construction work are low bids from the contractors, shoddy work and use inferior material during the construction, lack of control, welding problems, etc. According to the above main factors, we listed 20 secondary factors, e.g. bad financial situation, vicious competition, budget shortfalls, etc., and use analytical hierarchy process to find the relationship between them. In this thesis, there are in total 32 people have been interviewed, 8 of them are first-line supervisors (the up, middle and downstream of the steel plant, from steel-smelting plant, steel-rolling plant, public facility department to civil department.) Meanwhile, 10 senior executives are also interviewed; relevant literatures are used as related inference. Via this analysis, the most important factor of influencing the welding quality of new construction work is ¡§welding problem¡¨ with 0.297 rating point. Analyzing the third layer factors of low bids rating, the highest point is ¡§vicious competition¡¨ with 0.354. In shoddy work and use inferior material factor, ¡§changing subcontractor frequently¡¨ is the highest with 0.491 rating point. In false inspection, the ¡§progressing pressure¡¨ is the highest with 0.378 rating point. In welding problem, the ¡§construct without drawing¡¨ is the highest point with 0.371. In other factors, ¡§defected raw material¡¨ is the highest with 0.275 rating point. If the above problem solved, the welding quality in new construction work will improve tremendously. Keywords: non-destructive testing, quality of construction, new construction work, turnkey contractors, defect.

Thesis (M.S.)--Mechanical Engineering, Georgia Institute of Technology, 2004. / Berthelot, Committee Chair; Lynch, Committee Member; Jacobs, Committee Member. Includes bibliographical references (leaves 111-113).

Thesis (M. Phil.)--University of Hong Kong, 1981.

As of September 2007, there were over 67,000 U.S. bridges in the National Bridge Inventory classified as having unknown foundations. The bridges spanning rivers are of critical importance due to the risks of potential scour. In fact, over half of all bridge collapses are due to scour. Not only are these failures costly, they can be deadly for the traveling public. On April 5, 1987, ten people were killed in New York when a pier collapsed on the Schoharie Creek Bridge causing two spans of the deck to fall into the creek. Several other fatal collapses have occurred since the Schoharie Creek Bridge failure. Detecting scour is only part of the assessment that must take place to determine risk of failure and knowing the foundation depth is a critical component of the assessment. While this issue is not new, current techniques are typically invasive or costly. This research explores the feasibility and effectiveness of induced polarization (IP) and electrical resistivity imaging (ERI), near surface geophysical methods, for determining the depth of unknown foundations. In this work, forward models are created to ascertain the effects of the bridge layout on data quality such as varying depths and the impact of adjacent foundations on the foundation in question. Next, an experimental study is conducted at a National Geotechnical Experimentation Site (NGES) to further identify key parameters for the testing design and setup in order to obtain optimal surveys of bridge foundations. The conclusions of the forward modeling and NGES investigations are used to plan the field surveys on four bridges with known foundations. The outcomes of the four bridges show that IP and ERI can be used in concert with one another to estimate the type and depth of bridge foundations. The results of the field surveys are used to create a probability of non-exceedance curve for future predictions of unknown bridge foundations using the methods described in this research.

No description available.