13th International Conference on Fracture June 16–21, 2013, Beijing, China -8- Shear failure I II Figure 14. Typical shear damage of lattice struts due to axial tensile loading. Left: Shearing of the struts after tensile testing. Right: Shear fracture of a single strut after tensile testing. Note that the interior (I) and the exterior (II) exhibit differences in fracture appearance. Figure 15. Strut failure of hybrid specimen. Figure 16. Fracture of as-manufactured surface. A skin of partly molten material is obvious. 4. Discussion By comparison of data in Figure 11 and Figure 12 it is obvious that a superpositioning of stiffness for a tube and an open lattice structure does not equal the stiffness of a hybrid specimen. A conclusion must be that in tension the stiffness of a hybrid specimen is mainly influenced by the stiffness of the tube. I.e., for the tube the relation is according to Equation 2. ol t hm E E E < + (2) Regarding strength, in Figure 12 it is shown that for the geometry investigated here, the load is shared between the lattice structure and the tube so that the load applied to cause yield in the hybrid specimen equals the load applied to a tube and an open lattice as indicated by Equation 3. ol p t p p hm F F F 0.2, 0.2, 0.2, + = (3) The same analysis for maximum load before failure yields that the maximum load in the hybrid specimen is slightly higher compared to the load in a tube and the open lattice superpositioned as described by Equation 4.
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