PSI - Issue 18

Dan Ioan Stoia et al. / Procedia Structural Integrity 18 (2019) 163–169 Dan Ioan Stoia, Liviu Marsavina/ Structural Integrity Procedia 00 (2019) 000–000

164

2

big step forward in custom manufacturing, but obtaining parts that met the geometric and mechanical requirements is a challenging issue, as Salmoria et al. (2007), Pham and Gault (1998) and Es-Said et al. (2000) presented. The influence of the parts orientation in the building envelope and the anisotropy in the growing direction have been evidenced by Berti et al. (2010) for alumide, and by Stoia et al. (2019) for polyamide, both using selective laser sintering. The analysis of dimensional aspects in additive manufacturing and the correlation of those with technological factors have been studied by Galantucci et al. (2015), Nuñez et al. (2015) and Lieneke et al. (2016). The dimensional control varies from the order of hundreds of millimetres to 2-3 tenths of millimetres according to the technology used or the process parameters. In many situations, the poor dimensional control is associated with curling and wrapping phenomenon as Mousa (2006) presented in his study. Beside geometrical approach, mechanical characterization is another important aspect. The elastic properties and mechanical strength of polyamide were determined in tensile testing by Pilipović et al. (2018) and Dizon et al. (2018), according to laser energy density and part orientation. Taking into account the printing directions and shell thickness, Ahmed and Susmel (2018) build a large number of notched specimens in order to determine the fracture toughness and to investigate the accuracy of linear-elastic Theory of Critical Distances. Efforts on describing the fracture behaviour of metallic materials by laser melting technology have also been made by Razavi and Berto (2018) and Solberg et al. (2018)

Nomenclature P

laser power

v

velocity of laser beam

Ss

scan spacing energy density

ED

T 1 T 2

building chamber temperature removal chamber temperature

t f

layer thickness scaling factors orientation angle maximum force displacement

θ

F max.

δ a

notch length L, W, B length, width and thickness of the specimen E bend flexural modulus σ bend flexural strength K Q conditional value K IC fracture toughness

2. Materials and methods 2.1 Sample fabrication

The additive manufacturing process was carried out on EOS Formiga P100 (EOS GmbH Electro Optical Systems) laser selectively sintering machine. The material used in sample fabrication was Alumide powder. Alumide is an EOS material that consist of a mechanical mixture between PA 12 and aluminum particles. The main purpose of introducing aluminum in the mixture is to enhance the stiffness of the parts and to control the shape stability. The beam shape geometry of the specimen was constructed in SolidWorks 2013 according to the specifications of ASTM D 5045-99 (Fig. 1).