Deriving a strain based local structural element concept for the fatigue approach of additive manufactured aluminum components 2019-01-0525
In order to get an advantage of light weight design potentials the process induced material behavior of additive manufacturing has to be considered. This means in case of the aluminum alloy AlMg10Si on the one hand the influence of heat treatment, microstructure, support structure and the surface conditions and on the other the influences of load history and the interaction of these influences have to be considered in order to perform a high quality fatigue assessment.
Due to the material property gradients a local material based concept like the local strain concept should be the first choice. The fundamental idea of this fatigue approach concept is to descript the material behavior of an infinity material volume. Normally polished specimens are used to derive the cyclic material properties in order to describe the stress-strain-curve and the strain-life curve by performing strain controlled fatigue tests.
Within the framework of a numerical fatigue approach the real geometry and the local material behavior has to be considered. In case of additive manufactured structures this causes two challenges: Primarily the surface is rough that would lead to a very detailed FE-geometry model. Secondary due to the lightning strategy with different parameters for the rim and the bulk a metallurgic notch will occur within the transition from the surface e.g. rim to the bulk material. At the end the numerical afford is increasing.
In order to reduce this complexity a strain based structure element fatigue approach concept will be introduced. The fundamental idea is to describe the local component behavior by a structural property and follow the idea of the local strain concept. By using structural element strains and structural element stresses instead of local strain and local stress integral properties are used which reduce the number of experiments to derive the material properties and beyond that the complexity of the FE model.
Rainer Wagener, Benjamin Möller, Tobias Melz, Matilde Scurria
Fraunhofer Lbf, Fraunhofer Institute LBF, Fraunhofer LBF