13th International Conference on Fracture June 16–21, 2013, Beijing, China -4- 2.2. Geometry Different structures with and without lattices have been evaluated in the current work. Cross sections of the tubular shell, lattice and hybrid structures included are shown below, Figure 5. The lattice structure is designed to have a comparable density throughout the range of available dimensions. The measure d/l was kept constant throughout manufacturing of all test bars. As mentioned above, tensile testing was done using a “diamond” structure on the three different types of specimens a hollow tubular, an open lattice truss structure and a hybrid consisting of a tube containing a lattice truss structure as shown in Figure 5 containing the three different types of lattice truss structures. The structure sizes are called 2,2, 2,6 and 3,0 because of the dimensions that are calculated with the formula w/s=v where w = cell size, s = lattice diameter and v is value that needs to be less than three for the structure to be manufactureable. The specimen sizes were chosen to be (LxWxD), Lx15x15mm and Lx13x13mm for the open lattice truss structure. Figure 5. Cross-section of the three geometries for mechanical testing and evaluation of lattice truss structure testing: hollow shell (left), lattice truss structure (middle) and hybrid (right). Tensile strength tests were done on laser sintered Alloy X at build angles of 0° and 90°. The results show that the mechanical properties vary considerably depending on the build angle. Build angle is defined with the specimen compared to the build platform and shown below, Figure 6. x y x y x y z α = 90° α = 45° α = 0° α α Figure 6. Definition of specimen build and loading direction relative to the build platform plane. A specimen “0°” would be a specimen in any direction in the build plane and a specimen “α°” (0° < α < 90°) would be a specimen built out of the build platform. An angle α = 90° would indicate a specimen being built parallel to the SLM equipment build direction. 3. Results 3.1. Solid test bars
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