Fatigue of engine materials - TMF and TMF/HCF interactions
Purpose and goal
To improve efficiency and reduce emissions from internal combustion engines the pressure and temperature will increase, which means that the thermal and mechanical loads in the components also increases. In the current project, the thermo-mechanical fatigue (TMF) and TMF combined with high cycle fatigue (HCF) for materials relevant to cylinder heads and exhaust manifolds have been studied. The project objectives, to characterize the fatigue mechanisms and to develop a model that can predict the life of specimens subjected to combined TMF and HCF loads have been reached. In general, new improved methods for estimating fatigue life leads to shorter development times and that the need for expensive full-scale experiments are reduced and thus decreases the time to market of new components. Furthermore, the qualitatively understanding of the TMF and TMF/HCF fatigue mechanisms as well as the quantitative material data obtained will be used to give specific advice on the design of new engine components. The strategy applied to reach the project goals has been to perform an extensive experimental investigation in order to have a rich physical idea of the fatigue processes which in turn has been used to estimate the fatigue life as the load condition is varied. The experimental work has been used to develop a fatigue life model based on crack propagation that successfully has been used to predict the life of different grades of cast iron subjected to combined thermomechanical and high cycle fatigue loadings.