PSI - Issue 42

Ralf Lach et al. / Procedia Structural Integrity 42 (2022) 3–8 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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only very little) on the mechanical performance, these parameters are lower when compared to the ones obtained from compression-moulded samples. This is due to the porosity of 3D-printed materials. The ICIT results of the fracture mechanics investigations at impact bending are shown in Fig. 3. In Fig. 3a it can be clearly seen that for ABS the printing speed is only slightly having an effect on the toughness parameter as resistance against unstable crack initiation; this likewise applies for both the energy-determined (J values) and deformation-determined (CTOD) values. The building direction (45°/45° and 0°/90°) and thus the orientation has a strong effect on the crack propagation behaviour of ABS. ABS is generally very well suited for 3D printing, this is further confirmed when comparing conventionally manufactured specimens (i.e. specimens cut from compression moulded plates) to the 3D-printed ones with a building direction of 45°/45°. This comparison results in similar toughness parameters.

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ABS PC

ABS PC

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Elastic modulus (MPa)

Tensile strength (MPa)

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60 mm/s 60 mm/s 80 mm/s 80 mm/s Compression 45°/45° 0°/90° 45°/45° 0°/90° moulded

60 mm/s 60 mm/s 80 mm/s 80 mm/s Compression 45°/45° 0°/90° 45°/45° 0°/90° moulded

Fig. 2. Tensile strength (a) and elastic modulus (b) of ABS and PC.

Besides the higher scatter of the values, the statements already made for ABS can be also applied for PC in the same way (Fig. 3b). However, there is no general agreement between the toughness parameters of 3D-printed and conventionally manufactured specimens, i.e. PC is of less use in 3D printing.

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J value CTOD

J value CTOD

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CTOD (10 -3 mm) 6 12 18

CTOD (10 -3 mm)

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J value (N/mm)

J value (N/mm)

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60 mm/s 60 mm/s 80 mm/s 80 mm/s Compression 45°/45° 0°/90° 45°/45° 0°/90° moulded

60 mm/s 60 mm/s 80 mm/s 80 mm/s Compression 45°/45° 0°/90° 45°/45° 0°/90° moulded

Fig. 3. Fracture mechanics parameters (J values and crack-tip opening displacement CTOD) as resistance against unstable crack initiation at impact loading conditions depending on the processing parameters for ABS (a) and PC (b).

Observing the linear relationship between work of fracture and ligament length presented in Fig. 4a it can be concluded that the EWF method can be applied when working with ABS. The other preconditions to make this method applicable, such as the self-similarity of the load – displacements diagrams, are fulfilled as well. The related fracture mechanics parameters (w e and  w p ) can be obtained by plotting the specific work of fracture versus ligament length and subsequent linear fitting. The advantage of the EWF method is that no microfractographic analysis of fracture surfaces to determine stable crack growth is required, which highly qualifies the method for 3D printed materials. This must be seen also in the context of the problem that the stable crack growth to determine R