**9. Results**

Material properties between core-filled model and core-spaced model are investigated. All models are based on aluminum alloy AlSi10Mg and they are made by the 3D printing DMLS technique. Finally, 4D cube models defined as corefilled as Type 1 and core-spaced as Type 2 are tested by compression. Thus, Type 1 shows a higher Young's modulus, compressive yield strength, compressive ultimate compressive strength, and compressibility. The reason is that Type 1 can endure outer loads with a diagonal truss connected with inside hexagonal truss structure. However, Type 2 can be broken easily because they do not have a diagonal truss supporting. It is simply connected with outer or inner hexagonal structure without a cross truss. Thus, Type 1 shows a general shape of compressive tested line on **Figure 9**.

However, Type 2 shows an elastic line, yield, plateau, and up down line in **Figure 9** as in test 3 and test 4. Here, the interest is in the up down line. When it is tracked by broken specimens, it is identified as a reason; that is, when specimens are made by the 3D printing DMLS skill, laser melt metal powder at first and then the

**Figure 11.** *Crushed samples shown as arrows: (1) core-filled model. (2) core-spaced model.*

melted metal is added on each side of the truss clot by clot. Thus, each clot does not create perfect solid shape and it is not precisely connected with each truss. These are shown in **Figure 9**. Therefore, due to these reasons, material properties for 4D cube models made by the 3D printing DMLS skill show lower than solid material properties. Based on broken section in the sample (1) or (2) shown in **Figure 11**, there shows two issues. One is that melted metals are not connected with each other like a solid precisely. Due to this reason, connected sections in each model as Type 1 or Type 2 are easily broken after outer loading. These are shown as arrows in **Figure 11(1)** and **(2)**. The other one is there shows a space in additive layer when additive manufacturing makes a shape of specimen. Because of the space in the additive layer, each truss created by melted metals does not have enough to support outer loadings.
