Fatigue failure of metals is one of the aspects of material behavior that have not been explained through direct calculations or mathematical... Show moreFatigue failure of metals is one of the aspects of material behavior that have not been explained through direct calculations or mathematical modeling. This research is to undertake the development of an innovative model that can be used in predicting the fatigue behavior of metals. This model is based on the behavior of a system of large number of parallel elements, each composed of two springs, a string, and a mass block, that undergo cyclically varying or random load cycles. Failures among the elements occur at random and can be used as a means to simulate fatigue damage and fatigue behavior. Initial studies on this model have produced promising results. This research is intended for full development and implementation of the model including procedures for Development of a method for calibration of the model parameters using the common mechanical properties of steel, extension of the model to incorporate the hysteresis behavior of steel under cycling loading, and development of Constant Fatigue Life diagrams Such as Goodman diagram. Show less
A new method for reliable fatigue life prediction in metal structural components is developed where uncertainties are quantified using... Show moreA new method for reliable fatigue life prediction in metal structural components is developed where uncertainties are quantified using interval variables. Using this crack-initiation-based method, first, the uncertainties in laboratory test data for the fatigue failure of a structural detail are enumerated. This uncertainty quantification is performed through an interval-based enveloping procedure that relates the interval stress ranges to the number of cycles to failure, leading to the construction of an interval S-N relationship. Next, the uncertainties in field test data are enumerated in the extremum values of each stress range, as intervals, leading to the construction of interval stress ranges. For both the laboratory and field data uncertainty analyses, the mean stress effects are considered. Next, the interval damage accumulated over the duration of the field data is determined using the constructed interval S-N relationship and the obtained interval stress ranges. Then, the interval existing damage and interval remaining life are determined. Finally, as a conservative measure, the minimum remaining fatigue life is obtained in which all uncertainties are considered. Three numerical examples illustrating the developed method are presented, and the results are compared with results obtained by both Monte Carlo simulation and optimization. Using this method, for the numerical examples considered, it is shown that the results for bounds on the existing damage and the remaining fatigue life are sharp. Moreover, due to its set-based approach, the method is significantly more computationally efficient when compared with iterative procedures. Show less
