No description available.

No description available.

No description available.

Capacitor discharge welding (CDW) is a rapid solidification joining process under the influence of one-dimensional thermal gradients. Although CDW is useful for joining small parts and dissimilar metals, CD welded joints have a large variability in weld strength. CDW is not widely accepted because of a lack of automated process control. Studying the sources of variability in the CDW process can guide the automation of CDW. Therefore, the objectives of this study were to investigate sources of variability that affect weld strength and to generate a model to predict the weld strength variability in CDW. The source of variability was investigated by using screening experiments. Four different materials, stainless steel, Nitronic 50 Steel, copper, and low oxygen copper (C101), were selected to represent various levels of thermal conductivity and absorbed gas content. Thermal conductivity, percentage of gas content absorbed, diameter, and welding time were treated as the independent variables while the dependent variables were the standard deviation of CD weld strength as a percentage of base material strength and the mean of CD weld strength as a percentage of base material strength. A screening experiment and a statistical analysis of the data were used to develop a predictive model of the weld strength variability in CDW. Electron photomicrographs of weld fracture surfaces and dynamic current and resistance curves for each welding cycle were used to support conclusions from the statistical analysis. Conclusions of this study are that thermal conductivity and absorbed gas content do have a significant influence on weld strength variability in CDW. / Graduation date: 1999

Thesis (Ph. D.)--Lehigh University, 2002. / Includes vita. Includes bibliographical references (leaves 143-159).

The tubular welded joints used in the construction of Offshore structures can experience millions of variable amplitude wave induced stress cycles during their operational life. Fatigue has been identified as the main cause of degradation of structural integrity in these structures. As a result, fatigue is an important consideration in their design. Jack-up legs are made from a range of high strength steels with yield strengths up to 70OMPa. These steels are thought to exhibit fatigue resistance properties which are different when compared with conventional fixed platform steels such as BS 4360 50D and BS 7191 355D. The difference in their behaviour was heightened by the discovery, in the late 80s and early 90s, of extensive cracking around the spud can regions of several Jack-ups operating in the North Sea. It was thought that these steels may be more susceptible to hydrogen cracking and embrittlement. There was the additional requirement to study their behaviour under realistic loading conditions typical of the North Sea environment. This thesis contains results of an investigation undertaken to assess the performance of a typical high strength weldable Jack-up steel under realistic loading and environmental conditions. Details of the methodology employed to develop a typical Jack-up Offshore Standard load History (JOSH) are presented. The factors which influence fatigue resistance of structural steels used in the construction of Jack-up structures are highlighted. The methods used to model the relevant factors for inclusion in JOSH are presented with particular emphasis on loading and structural response interaction. Results and details of experimental variable amplitude corrosion fatigue (VACF) tests conducted using JOSH are reported and discussed with respect to crack growth mechanisms in high strength weldable Jack-up steels. Different fracture mechanics models for VACF crack growth prediction are compared and an improved generalised methodology for fast assessment of Offshore structural welded joints is proposed.

Thesis (M. Phil.)--University of Hong Kong, 1999. / Includes bibliographical references (leaves 124-127).

No description available.

Thesis (Ph. D.)--Oregon Graduate Center, 1982.

Thesis (Ph. D.)--Lehigh University, 2000. / Includes vita. Includes bibliographical references (leaves 306-314).