PSI - Issue 21

E.F. Akbulut Irmak et al. / Procedia Structural Integrity 21 (2019) 190–197 E. F. Akbulut Irmak et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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1. Introduction The selective laser melting (SLM) production method is classified as one of the layer-based and powder-bed-based additive manufacturing technologies. Selective laser sintering (SLS) method, which is one of the same production technologies, shows some similarities when considering the machines and the equipment used. The difference between the two production methods is due to the binding mechanism of the powder particles. The complete melting of the raw material used in the SLM is possible to produce almost full density parts in a single manufacturing step. Yadroitsev and Smurov (2010) studied on the production of high-quality components with various materials. Kempen et al. (2011) investigated AlSi10Mg powder as a raw material and developed process control optimization. The results of the study on mechanical properties of the material were presented by Kempen et al. (2015) and they showed that material properties are highly influenced by adjusting the applied laser power, scanning speed and layer thickness, such as a suitable scanning pattern. The residual porosity of AlSi10Mg components is the overlap of metallurgical pores and keyhole pores that vary in proportions according to the selected process parameters. Kleszczynski et al. (2013) executed a research on possible process errors, which are important in terms of mechanical properties. Due to layered production and numerous directional dependencies, the manufactured components are considered as anisotropic materials. This raises the question of how to evaluate the quality of parts manufactured by the SLM method. The porosity originated from the dissolved gas in the raw aluminum powder, which is likely to be hydrogen. Thus, the effect of drying the raw material in powder form before consolidation was examined and as a result, positive effects on density were observed. The concept of good mechanical properties generally requires the consideration of grain size and orientation and the density is widely used as the first indicator of quality, Hitzler et al. (2016). The influence of the orientation dependence on the mechanical properties of SLM materials results in important scatter in yield strength and fracture formation in all directions due to the inhomogeneities induced by SLM manufacturing technology. The prediction of the fracture limits by conventional damage parameters of AM materials is a big challenge in order to understand the physical mechanism well. It is necessary to be aware of the defects in the structure. It is known that trends in fracture limit are directly related to porosity in the structure. Fracture curve depending on stress triaxiality is the reduced form of fracture surface. In the study, fracture framework GISSMO, which is based on an incremental damage accumulation, was applied, Andrade et al. (2016). The orientation dependencies in the specimens were studied. Quasi-static tensile tests were performed to achieve further insight into the mechanical properties. Furthermore, it is seen that the tendencies in the mechanical properties of the material are also related to the porosity distribution in the structure. Simulation of mechanical behavior is essential for detailed investigation. In order to investigate the porous material, 3D FE models with pores are significant to provide an accurate description of the actual structure. This study contributes to previous researches on SLM AlSi10Mg materials by taking into account the solid element modeling with randomly distributed pores. The objective of the present work is to investigate the plasticity and fracture behavior of SLM AlSi10Mg flat specimens, which have a high amount of pores in the structure. Additively manufactured specimens are therefore modeled with randomly distributed pores and simulated. It is seen that in addition to the anisotropy effect, heterogeneity of the material has a high impact on the deformation response. 2. Methodology 2.1. Manufacturing process In the current research, SLM 250 HL machine model from SLM Solutions GmbH equipped with a 400 W YLR- Fiber-Laser and a building chamber with the dimensions 250*250*350([mm] x*y*z) was used. Argon was selected as the inert gas. Constant building platform temperature was set at 200°C. The raw AlSi10Mg powder with the particle size distribution of 20-63 µm was provided by SLM Solutions GmbH. Particle shape is spherical and the raw material has high flow ability. Exposure strategy for the volume area was in the shape of stripes (10 mm, 79° layer rotation). Detailed manufacturing parameters are presented in Table 1.