Multi-axial fatigue for predicting life of mechanical components

The work presented in this dissertation is directed towards the development of a generalized procedure for predicting structural fatigue damage in metals using the finite element method. The work is concerned with the general service life of metallic components. This considers the effect of the constantly varying orientation of strain on mechanical components. Fatigue life in the context of this dissertation is the number of repetitions of a load history until crack initiation. This dissertation is not concerned with crack growth and ultimate material failure resulting from the growth of cracks. These aspects of fatigue of metallic components are well established through available literature.;The dissertation will develop and apply techniques of using stress and strain fields obtained from finite element analysis (FEA) for predicting the extent of structural fatigue damage. The problem is formulated in the general three-dimensional case, Global material nonlinearities may be considered in the FEA analysis without affecting the methods presented in this dissertation.;Developed in this dissertation is an energy-based approach for modeling fatigue damage. This approach is developed by modifying the Smith-Topper-Watson damage model. A strain energy scaling function is developed to account for the variations in strain orientation.;Software is developed for interfacing with FEA programs and calculating fatigue damage results based upon the prescribed duty cycles. The results are then written to the finite element program for post processing. The data available for post processing is the maximum damage value and the orientation of the damage vector. Damage is accumulated via Miner's rule.;Also presented in the dissertation are experimental and analytical studies of two mechanical components. The first component is a study of fatigue of muffler support bar used on a motorcycle. This is a steel component undergoing dynamic excitation. The second component is a motorcycle handlebar riser structure made from semi-solid forged aluminum.;The results of the methods presented here are compared to both experimental an analytical methods using established fatigue damage models. The methods developed in this dissertation compare well with other methods for fatigue damage prediction. Suggestions for further refinement of the techniques developed are discussed.