PSI - Issue 42

5

Liviu Marsavina et al. / Procedia Structural Integrity 42 (2022) 1259–1265 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

1263

0 = 1 2 .

(5)

4. The experimental results for PLA and PETG The maximum load F max from the tests was considered to calculate the nominal stress: = 6 2 where B and R are the SENB specimen dimensions and the bending moment Mi : = 4 (2 )

(6)

(7)

and ( 2S ) is the span, Fig. 2. The mean values of the nominal stress according with the experimental results for both materials are presented in Table 2.

Table 2. The nominal stress values for PLA and PETG materials. Specimen type Radius, R [mm] Span, ( 2S ) [mm]  N for PLA [MPa]

 N for PETG [MPa] 22.43  1.01 25.53  1.59 32.56  0.72 37.23  1.01

XL

40 30 20 10

64 48 32 16

18.25  0.80 21.44  0.77 30.84  0.49 37.66  1.53

L

M

S

Based on the linear regression analysis from Fig. 5 the fitting parameters A and C were determined and the energy release rate, size of the fracture process zone, stress parameter and transitional size were estimated based on eqs. (2) – (5) and are listed in Table 3 for the two investigated materials.

Table 3. The size effect parameters for PLA and PETG materials. Material Energy release

Size of fracture process zone, c f [mm]

Stress parameter  N0 [MPa]

Transitional size R 0 [mm]

rate, G f [N/mm]

PLA

4.28

2.785

65.93 64.51

2.785

PETG

10.01

5.68

5.68

The results of the asymptotic analysis are shown in Fig. 6. The plots of the nominal stress versus the size of the structure represents a smooth transition from the strength criterion to Linear Elastic Fracture Mechanics. This behavior was also observed from concrete, SiC ceramic material, sea ice, carbon composite, PVC foams, aluminium alloy, Bazant (2002). The tensile strength horizontal lines correspond to the tensile tests results obtained in dog bone specimens using the same printing parameters:  f,PLA = 50 MPa and  f,PETG = 52.7 MPa. The transitional sizes for the two investigated materials are R 0,PLA = 2.785 mm, respectively R 0,PLA = 5.68 mm (Table 3) which are below to the lower SCB specimens radius of 10 mm.