PSI - Issue 28

Mohammad Reza Khosravani et al. / Procedia Structural Integrity 28 (2020) 720–725 M.R. Khosravani and T. Reinicke / Structural Integrity Procedia 00 (2020) 000–000

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printing. For instance, 3D printing is now being used in aerospace Liu et al. (2017), medicine Moetazedian et al. (2020), electronics Khosravani and Reinicke (2020a), and automotive Nichols (2019). In 3D printing processes several materials can be used, namely: resins, plastics, rubber, metals, and ceramics. As application of 3D printing has been significantly increased in the past few years, di ff erent engineering aspects have been studied in this field Qian et al. (2020); Ezeh and Susmel (2020); Khosravani and Reinicke (2020b); Luo et al. (2020). Since additively manufactured parts experience various loading conditions in their practical applications, their strength, and fracture behavior have been studied over the years Solberg et al. (2018); Xu et al. (2019); Allum et al. (2020). For instance, in Li et al. (2018) experimental and numerical investigation were performed on 3D-printed polymers. In detail, acrylonitrile-butadienestyrene (ABS) material was used in fabrication of specimens based on the fused deposition modeling (FDM) method. A series of tests was conducted on the single edge notch tension specimens printed under di ff erent raster orientations. The obtained results confirmed that fracture properties are highly depend on the raster orientations. Moreover, it was claimed that strength and fracture toughness of the parts can be improved by topological patterns on the surface of the component. Subsequent experiments were performed to determine plastic behavior of 3D-printed titanium alloy Bressan et al. (2019). More in deep, 3D-printed Ti-6Al-4V were built based on the powder bed fusion technique and examined by a series of fatigue tests. The documented results of tests indicated that the fatigue life was similar regardless of layer orientation and heat-treatment. Moreover, it was reported that the heat-treated parts showed a higher energy absorption. Recently, in Shang et al. (2020) e ff ect of structural parameters on fracture patterns of sinusoidally 3D-printed composites was investigated. In this context, additively manufactured parts based on continuous fiber reinforced composite were fabricated. Researchers performed tensile tests perpendicular to the fiber direction and determined tensile modulus and tensile strength. The achieved results confirmed that increase in the amplitude and frequency of the sinusoidal path has led to increase in tensile modulus, tensile strength, and fracture energy absorption of the examined specimens. In the current study, the influence of two printing parameters on the mechanical behavior of 3D-printed parts has been determined. More in deep, the specimens were printed under di ff erent (a) raster layups, and (b) printing speed. By tests of specimens, e ff ects of the aforementioned printing parameters have been investigated. This paper is organized as follows: Section 2 describes specimen preparation. Details of experimental tests are explained in Section 3. Section 4 then presents the obtained results. Finally, Section 5 outlines conclusions.

2. Specimen preparation

The dog-bone samples are first drawn in a CAD platform and then saved as ”.stl” format. The 3D model data are transferred to a 3D printer where polylactic acid (PLA) was used for fabrication of the specimens. Table. 1 presents printing and utilized material parameters.

Table 1. Printing and material parameters. Printing parameters

Value

PLA properties

Value

Nozzle temperature ( ◦ C) Layer thickness (mm) Bed temperature ( ◦ C)

Melting point ( ◦ C) Glass transition ( ◦ C) Density (gr / cm 3 )

215 0.4

∼ 160 ∼ 65 1.21 1968

55

Number of contours

2

Moisture absorption (ppm)

In order to determine the e ff ects of 3D printing parameters on mechanical and fracture behavior of the 3D-printed parts, two di ff erent parameters were changed: raster layup and printing speed. Although specimens were printed with di ff erent raster layups and printing speed, all other 3D printing parameters were kept constant. Raster direction is defined as the printing direction relative to the loading direction. Printing speed defined as the distance traveled by the extruder along the bed per unit time while extruding. All the specimens were produced in 8 layers with unidirectional layup and di ff erent raster orientations: [0 ◦ ] 8 , [30 ◦ ] 8 , [45 ◦ ] 8 , [60 ◦ ] 8 , and [90 ◦ ] 8 . The mentioned angle shows the printing direction with respect to loading direction. Also, the subscripts denote the number of layers. The above-mentioned specimens were printed under two di ff erent printing speeds: 20 mm / s and 80 mm / s. The flat-dog-bone shaped samples were printed according to ASTM D638 (2014). In Fig. 1 the geometric model and fabricated specimens with di ff erent