PSI - Issue 35

Mohammad Reza Khosravani et al. / Procedia Structural Integrity 35 (2022) 59–65 M.R. Khosravani and T. Reinicke / Structural Integrity Procedia 00 (2021) 000–000

62

4

ometry was created using a CAD software package and exported as a stereolithography file (STL) and loaded into a 3D printer slicing software package (Eiger, Markforged ). Using this software is necessary to control the placement of the fiber reinforcement. In the current study, nylon filament with diameter of 1.75 mm was used as thermoplastic matrix. Moreover, fiberglass with diameter of 0.3 mm was used as reinforcement. Table 2 presents some material properties of utilized nylon and fiber. In this study, specimens are divided to two groups (unreinforced and reinforced) and nine samples were tested in each group. Once the packaged material was opened, it was stored in a dry box in order to minimize moisture absorption. It was also performed for the fabricated specimens prior to the testing.

Table 2. Some material properties of utilized nylon and fiber. Material properties

Nylon

Fiberglass

Flexural strength (MPa) Flexural modulus (GPa) Tensile strain at break (%)

50

200

1.4 150

22

3.8 105

Heat deflection temperature ( ◦ C)

41

Density (g / cm 3 )

1.1

1.5

In the current study, the dog-bone shaped specimens were printed with layer thickness of 0.1 mm. Since specimens were printed in forty layers, total thickness was equal to 4 mm. During the printing process, nozzle temperature was 275 ◦ C. Fig. 2 shows printing configuration of nylon and fiber reinforced specimens. There are two contours in all printed specimens and filaments at 45 ◦ with respect to the loading direction. The radius of fillet was equal to 76 mm and all specimens were printed according to the utilized standard with gauge length of 50 mm and width of 19 mm. It should be pointed out that a careful preparation of all specimen geometries was required to avoid damage initiation because of badly chosen fiber arrangements.

Fig. 2. Printing configurations of unreinforced (top), and fiber reinforcement specimen (bottom).

It is worth mentioning that the fiber layers were smoothly contoured by the floor and roof layers. In detail, the fiber reinforced specimens were printed with thirty layers of fibers and five layers of nylon in top and bottom as roof and floor layers. The Eiger slicing software does not allow an odd number of fibers. It should be noted that he mechanical properties of parts fabricated by FDM and FFF methods depend on the printing parameters. In this study, printing parameters such as feed rate, layer thickness, and fill density were kept constant in preparing all specimens.

4. Experimental program

In the present study, a series of uniaxial tensile tests was carried out under displacement control via constant cross head movement of 1 mm / min until failure. Indeed, a hydraulic machine was used to conduct the tests under static loading conditions. The machine was fitted with 15 kN load cell equipped with electronic control which monitors the applied load and movement of the top cross head. The displacement on the specimens was measured by using a linear variable displacement transducer. Fig. 3 shows a fiber reinforced specimen under test conditions.