13th International Conference on Fracture June 16–21, 2013, Beijing, China -7- where index “s” indicates superpositioned. “t” is tube and “ol” stands for open lattice. E is the stiffness (force/length) and Fp0.2 and Fm are force at yield and ultimate force. Due to the geometrical nature of the specimens, comparisons using these quantities are more convenient than quantities based on stress. 0 20 40 60 80 100 120 0 20 40 60 80 100 120 measured stiffness Em [kN/mm] superpositioned stiffness . Es [kN/mm] 0 10 20 30 40 50 0 10 20 30 40 50 measured Fp0.2 [kN] superpositioned Fp0.2 [kN] 0 20 40 60 80 0 20 40 60 80 measured Fm [kN] superpositioned Fm [kN] a) b) c) Figure 12. Comparison of superpositioned and measured stiffness E, load at yield Fp0.2 and maximum load before failure Fm for the hybrid geometry investigated in the current work. 3.3. Fracture surfaces Fractographic observations from solid test bars and lattice trusses are shown below, Figure 13 to Figure 16. Figure 13 show the ductile fracture surface of an SLM manufactured solid test bar. In Figure 14 the failure of an open lattice truss structure is shown. In Figure 15 and Figure 16 bulk and surface regions of a lattice specimen can be viewed. Figure 13. Typical cup and cone dimple fracture in solid as-manufactured alloy X manufactured by SLM (build and load direction perpendicular to build platform.
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