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The development of precise data for the effect of chemistry and processing variables on the fracture toughness of low to medium carbon cast steels, is paramount to an increased understanding of the fracture behaviour of these important engineering materials. This knowledge would, in itself, lead to improvements in alloy development/selection rationale and increased cast steel usage, particularly in critical areas. / Toward this end, an investigation into the influence of Cr, Mn and Ni additions on the room temperature fracture toughness and flow properties of 0.30, 0.40 and 0.55 wt% C cast alloys was conducted. In order to avoid the chemical and processing complexity normally associated with commercial castings, the study was undertaken on heavy section castings produced in the laboratory from melts composed of commercial purity ingredients. Measurements were conducted on three-point bend test pieces machined from heat-treated castings. The fracture toughness techniques used included LEFM (K(,IC)), J integral and COD ((delta)(,c)). A potential drop method was employed to record crack initiation. / Very high room temperature fracture toughnesses were achieved in the majority of the alloys examined, with only three alloys having K(,IC) values of less than 150 MN.m('-3/2) or COD, (delta)(,c), values of less than 0.1 mm. Further, yield stress ((sigma)(,ys)) values were found to lie within 80-105% of those recorded for commercial castings of comparative composition. / At the 0.30 and 0.40 wt% C levels it was found that the room temperature fracture toughness of the alloys was relatively independent of the microstructure as well as the amount and particular addition element employed, although variations in the tensile properties were noted. / At the 0.55 wt% C level significant differences in the fracture behaviour were caused by the individual element additions. Manganese was found to improve the toughness of the high carbon alloys, while nickel produced little change and chromium had a negative effect on toughness. In each case the influence of these elements was manifested in microstructural differences. / The results of this study are reviewed in the light of the limited data available from commercial cast steels and the need for improved toughness performance without undue loss of yield strength and other properties. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of author.) UMI

The current research work investigates the behaviour of steel and composite beams as well as beam-to-column connections at elevated temperatures. Significant attention is needed to identify the main issues. as the behaviour is profoundly different from that at ambient temperature. Local buckling of the beam flange outstands has been found to be highly significant in accelerating the development of catenary action in fire, since this action is reliant on hinges forming which may result from local buckling. Local buckling of the beam web, which experiences a non-uniform temperature variation, is also important because the mechanical properties of the steel are degraded non-uniformly from their ambient values. Current formulations for web buckling at ambient temperature therefore need substantial revision at elevated temperatures. Very large compressive forces are developed within the beams initially and these induce large stresses in the column web; hitherto this has not been considered. Developing a formulation representing the mechanics of this potential failure zone in the column web in the compression region of the connection is a useful and needed addition to research in the topic. Predicting the critical temperature in a connection that causes failure of the bolts, end plate and column flange in the tension zone of the connection is considered in this research work. An elastic analysis of a panel zone in a rigid or semi-rigid joint in a steel frame, which is based on simple equilibrium considerations that takes into account the shear and flexural deformations of the panel zone, is developed at elevated temperatures. In order to model the structural response of a composite beam restrained by cooler members in a steel compartment fire in a frame structure at elevated temperature, recourse is needed to a geometric nonlinear formulation, since the beam transverse deflections are not negligible and the axial eompressive force in the member is also substantial at the early stages of the fire. This thesis presents such a formulation, which incorporates partial interaction between the concrete slab and steel component, as well as the degradation of the stiffnesses of the components of the composite beam prior to yield at elevated temperature.

Thesis (Ph.D.)--University of Wollongong, 2004. / Typescript. Includes bibliographical references: leaf 192-205.

Thesis (M.S.)--University of Missouri, School of Mines and Metallurgy, 1924. / The entire thesis text is included in file. Typescript. Title from title screen of thesis/dissertation PDF file (viewed June 19, 2009)