No description available.

published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

The overall objective of this study is to develop methods for providing a statistical summary of material fatigue stress-life (S-N) data for engineering design purposes. Specific goals are: (1) Development of an analytical model for characterizing fatigue strength. This model would include: (a) a description of the trend of the data (e.g., the median curve through the data), (b) a description of the scatter of the data (e.g., the standard deviation of N as a function of S), and (c) the statistical distribution of N given S or S given N. (2) Development of an algorithm for constructing a design curve from the data. The curve should be on the safe side of the data and should reflect uncertainties in the physical process as well as statistical uncertainty associated with small sample sizes. (3) Development of a statistical model that can be applied in a structural reliability analysis in which all design factors are treated as random variables. Significant achievements are: (1) Demonstration, using representative fatigue data sets, that the bilinear model seems to provide a consistently adequate description of the trend of fatigue data. (2) Demonstration, using representative fatigue data sets, that the pure X error source model seems to provide a consistently adequate description of the uncertainties observed in heteroscedastic fatigue data. The pure X error source model is based on recognition of the uncertainties in local fatigue stress. (3) Development of a procedure for constructing a design curve using the tolerance limit concept developed by D. B. Owen. A more practical simplified or approximate Owen curve was shown to have a minimum loss of confidence level, relative to exact Owen theory, under fairly general conditions. (4) Recommendations for methods of developing a statistical model for reliability analysis. A comprehensive study of this issue was not pursued.

published_or_final_version / abstract / Industrial and Manufacturing Systems Engineering / Master / Master of Philosophy

The interference-fit joint is widely used in machine design to connect two cylindrical machine elements. Its popularity comes from the simplicity of the assembly and the low cost of the production process. Even so, no study has examined the boundary non-linearities in the assembly of these joints. Moreover, the contact stresses and the stress concentration factors in interference-fit joints under torsional loads have not yet been examined in detail. In addition, the interface stresses and stress concentration factors in interference-fit joints subjected to bending loads have not been approached theoretically before. The sugar-mill roller is one of the oldest and most important examples of the interference-fit joints. The frequent fatigue failure of the sugar-mill rollers under reversed bending causes costly emergency line-shut downs. The versatility of the finite element method and the capability of the point-matching technique in handling contact problems have been combined, in the present work, to produce a surface-matching technique. It has been found that the complete-cohesion contact assumption may be acceptable for coefficients of friction ≥ 0.2, which is the case for most of the normally machined surfaces. An approach combining the semi-inverse displacement finite element method and the surface-matching technique has been developed to perform the torsional analysis. It has been found that the governing non-dimensional quantities are the ratio of the cohesion-length to the interface-length and the coefficient of friction divided by the load-level. The load-level is the ratio between the angle of twist of the shaft per unit length when the torque acts on the shaft alone and the amount of the diametral interference divided by the shaft diameter. A finite element model, using 8-noded solid elements together with linear interface elements, has been employed to locate the cohesion and slippage-zones in the sugar-mill roller under bending. The contact pressure increases along the compression side and decreases along the tension side. On the contrary, the interface shear decreases along the compression side due to bending and increases along the tension side. Subsequently, a larger slippage-length has been detected along the tension side.

The Oregon Department of Transportation is responsible for many steel deck truss bridges containing connection details that are fatigue prone. A typical bridge, the Winchester Bridge in Roseburg, Oregon, was analyzed to assess the loading conditions, stress levels, and fatigue life of the connection details. The analysis included linear-elastic beam analysis, 2D and 3D finite element modeling, and fatigue modeling. A field identification methodology was developed to expand the analysis to other steel deck truss bridges. Five retrofit strategies were investigated to determine their effectiveness in reducing the stress ranges developed in the connection details. / Graduation date: 1998

Copies of author's previously published articles inserted. / Bibliography: leaves 254-264. / xx, 297, [26] leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Studies the effects of various weld geometry parameters, residual stresses and the combined axial and bending loadings on the fatigue behaviour of butt-welded steel joints. Presents ways of improving the fatigue strength. Simulates the effect of the induced surface compressive residual stresses on the welded joints (for the improvement of the fatigue life). Explains the phenomenon of large scatter band associated with fatigue tests results. Suggests a new procedure for performing and evaluating the fatigue tests. / Thesis (Ph.D.)--University of Adelaide, Dept. of Mechanical Engineering, 1996

Copies of author's previously published articles inserted. / Bibliography: leaves 254-264. / xx, 297, [26] leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Studies the effects of various weld geometry parameters, residual stresses and the combined axial and bending loadings on the fatigue behaviour of butt-welded steel joints. Presents ways of improving the fatigue strength. Simulates the effect of the induced surface compressive residual stresses on the welded joints (for the improvement of the fatigue life). Explains the phenomenon of large scatter band associated with fatigue tests results. Suggests a new procedure for performing and evaluating the fatigue tests. / Thesis (Ph.D.)--University of Adelaide, Dept. of Mechanical Engineering, 1996

The concise description of one- and multidimensional stationary and non stationary vehicle loading histories for fatigue analysis using stochastic process theory is presented in this study. The load history is considered to have stationary random and nonstationary mean and variance content. The stationary variations are represented by a class of time series referred to as Autoregressive Moving Average (ARMA) models, while a Fourier series is used to account for the variation of the mean and variance. Due to the use of random phase angles in the Fourier series, an ensemble of mean and variance variations is obtained. The methods of nonparametric statistics are used to determine the success of the modeling of nonstationarity. Justification of the method is obtained through comparison of rainflow cycle distributions and resulting fatigue lives of original and simulated loadings. Due to the relatively small number of Fourier coefficients needed together with the use of ARMA models, a concise description of complex loadings is achieved. The overall frequency content and sequential information of the load history is statistically preserved. An ensemble of load histories can be constructed on-line with minimal computer storage capacity as used in testing equipment. The method can be used in a diversity of fields where a concise representation of random loadings is desired. / Ph. D.

Bibliography: leaves 140-144. / xix, 156 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Determines the effect of partial-interaction and interfacial friction on the fatigue behaviour of composite bridge beams and develops a set of design rules for the assessment of the residual strength and performance of composite bridge beams. / Thesis (Ph.D.)--University of Adelaide, Dept. of Civil and Environmental Engineering, 1999