Influence of discontinuities on fatigue strength using the example of additively manufactured specimens made of AlSi10Mg

Abstract

Fatigue strength is largely affected by the influence of discontinuities: geometric notches like holes and corners in components, surface notches (roughness), pores and inclusions in the material. Therefore fatigue of structures and materials is a local problem and fatigue strength calculations are best carried out using local approaches such as local stress concept, local strain concept or fracture mechanical concepts. In this investigation, the influence of discontinuities on low cycle and high cycle fatigue strength of materials was examined on the example of additively produced material specimens made of aluminium AlSi10Mg by using a fracture mechanics parameter. Results of fatigue tests on hourglass-specimens made from four different series of 3-D printed specimens are presented. The examination of the fracture surfaces revealed that damage always started from pores located near the surface of the specimens. The fractography gave information about geometry, size and position of the crack-causing pores. The influence of such pores on the fatigue strength of the printed aluminium was investigated by using a modification of Murakami’s √area parameter. The common scatter band of the four test series could thus be reduced significantly.