PSI - Issue 51

J. Majko et al. / Procedia Structural Integrity 51 (2023) 160–165

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J. Majko et al. / Structural Integrity Procedia 00 (2022) 000–000

formation of cavities and stress concentrators. Therefore, wet material printing with a nozzle temperature equal to the melting point of dry nylon can negatively influence mechanical properties. Therefore, the nozzle temperature was adjusted to a value that would prevent material overflow. Experimental testing showed that adjusting the nozzle temperature to 225°C led to the elimination of the material overflow. The printing parameters defined in Table 2 were preserved. However, a decrease in nozzle temperature by about 50°C negatively affected the connection quality between the individual layers. This defect became apparent during the cleaning of the printing bed, and in some cases caused delamination of the specimens. For this reason, the authors decided to set the temperature of the printing bed to the maximum possible temperature of 110°C. The increase in the printing bed temperature eliminated the occurrence of apparent defects.

Fig. 3. Uncontrolled flow of wet material through the nozzle.

3. Tensile test results Each series consisted of five specimens. Tensile test was performed using INSTRON 5985 device. The outcomes of the test along with the specification of modified parameters are given in Table 3.

Table 3. Specification of individual series and average values of tensile test results.

Series

A

B

Orientation

0

0

Printing bed temperature [°C]

110 225 Wet

20

Nozzle temperature [°C]

273

Material

Appropriately stored Markforged MarkTwo

Printer

Prusa i3 1606.76

Ultimate force [N] Tensile stress [MPa]

1566.22

41.2

40.15

In both cases, the samples reached tensile strength of more than 40 MPa. The results showed that the printing of wet nylon reinforced with chopped carbon fibres is possible under certain conditions. Furthermore, the results demonstrate that the appropriately adjusted printing parameters lead to tensile strength values that are comparable to properly stored material.