Deriving strain based local structural element concept for the fatigue assessment of additively manufactured structures

Additive manufacturing offers new options for lightweight design for safety parts under cyclic loading conditions. In order to utilize all advantages and exploit the full potential of additive manufactured parts, the main impact factors on the cyclic material behavior not only have to be identified and quantified but also prepared for the numerical fatigue assessment. This means in case of the AlSi10Mg aluminum alloy to consider influences related to the exposure strategy, heat treatment, microstructure, support structures and the surface conditions, as well as the influence of the load history and finally the interaction of these influences in order to perform a high quality fatigue assessment. Due to these reasons, and with respect to the numerical effort, the cyclic material behavior of additively manufactured AlSi10Mg produced by selective laser melting will be discussed. With respect to the microstructure, as well as the manufacturing process, a local structure element will be derived for the fatigue assessment. Thus, an influence that may be directly induced by the manufacturing process, like pores and different microstructures, can be considered with the help of this new structure elements. Stresses and strains have to be interpreted as integral mean values of a defined local structure element, well knowing that the local stresses and strains could be higher due to stress concentrations e.g. in geometrical and metallurgical notches. Furthermore, influences on the fatigue strength or life caused by different surface conditions, can be considered by the use of the new structure elements. Finally, the influence of the glide character is taken into account in order to improve the numerical fatigue approach of cyclic loaded additive manufactured structures and components.