Fatigue Strength of Gray Cast Iron – New Insights Regarding the Size Effects

<div class="section abstract"><div class="htmlview paragraph">Gray cast iron (GJL) is one of the oldest cast iron materials and is still in use in many applications in the automotive industry due to its good characteristics, in relation to lubrication, heat conductivity and damping. Engine parts particularly benefit from these parameters. Nevertheless, the design of these components has always been challenging, in terms of maximizing material utilization for lightweight designs for components under cyclic loading. In particular, with regard to the influence of the statistical (component size), geometrical (notches) and technological (microstructural) size effects, the existing guidelines and literature lack the necessary information to provide a comprehensive understanding of the cyclic material behavior of GJL materials.</div><div class="htmlview paragraph">Within a comprehensive study, different GJL materials have been investigated at Fraunhofer LBF to provide more detailed information regarding the influence of size effects on fatigue strength. Accordingly, a variety of specimen geometries and microstructures were investigated under cyclic loading, providing the necessary data for a proper fatigue assessment of automotive components. Beyond the current standards, comparisons between the technological and the geometrical and statistical size effects were drawn between different microstructures. In this case, it appears that the specimen size, in terms of a highly stressed volume of a component, is not the only factor influencing fatigue strength, but also the superimposed microstructure. This paper summarizes the main results of this investigation in order to provide information for a design improvement, in terms of lightweight and efficiency.</div></div>