PSI - Issue 41

Mohammad Reza Khosravani et al. / Procedia Structural Integrity 41 (2022) 664–669 Mohammad Reza Khosravani et al. / Procedia Structural Integrity 00 (2022) 000–000

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2. Overview of FDM technique

The advancement of 3D printing made it possible to fabricate components with complex geometries. FDM is one of the most popular types of 3D printing which can be used for fabrication of structural elements with undercuts or cavities, are typically impossible to manufacture with conventional technologies. Similar to other 3D printing techniques, the FDM process is based on the principle of deposition / solidification of successive layers to form the digitally designed 3D shape. In the FDM process, plastic filament is usually melted in an extruder that simultaneously moves in the 3D vector space and deposits the material one layer at a time. Fig. 1 shows a schematic of the FDM process. Di ff erent thermoplastics such as PLA, ABS, and nylon can be utilized in manufacturing parts based on the FDM technique.

Fig. 1. A schematic of the FDM technique.

Although the FDM process has been widely used in many research and industries, extrusion-based 3D-printed parts showed low mechanical strength which can be improved by adjusting printing parameters. Indeed, parameters used in the printing process, such as the layer height, build orientation, raster width, infill percentage, nozzle temperature, and air gap can be adjusted to fabricate a 3D-printed part with higher mechanical strength.

3. Experimental procedure

3.1. Design and printing of specimens

In the current study, 3D-printed specimens were designed in a CAD platform according to configuration A in ASTM D5766 (ASTM D5766, 2018) with a width of 36 mm and thickness of 4 mm. Since ratio of the specimen width to the hole diameter ( w / D ) has influence on the structural integrity of the part, we have fabricated specimens with two hole diameters. Particularly, specimens with w / D of 3 (hole diameter: 12 mm) and 6 (hole diameter: 6 mm) were designed and fabricated in this study. We used PLA material for fabrication of specimens and in Table 1 physical and mechanical properties of utilized PLA are summarized.

Table 1. Physical and mechanical properties of utilized PLA material. Physical properties Typical value

Mechanical properties

Typical value

1.17-1.24 g / cm 3 7-11 g / 10 min

Density

Young’s modulus Bending strength Bending modulus Elongation at break

2636 ± 330 MPa 8.51 ± 2.9 MPa 3283 ± 132 MPa 1.9 ± 0.2%

Melt index

150 ◦ C 61 ◦ C

Melting temperature

Glass transition temperature

All specimens were fabricated using FDM technique with three contours and layer thickness of 0.2 mm including ± 45 ◦ layers with respect to the loading direction. During the printing process, nozzle temperature and printing speed were set to 220 ◦ C and 60 mm / s, respectively. Here, all specimens were printed with infill density of 100% and bed temperature of 50 ◦ C. As we discussed in our previous research works (Khosravani and Reinicke, 2020; Khosravani