PSI - Issue 33

Jamaloddin Jamali et al. / Procedia Structural Integrity 33 (2021) 832–842 Author name / StructuralIntegrity Procedia 00 (2019) 000–000

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The tensile test was performed according to ASTM D638 in order to obtain relevant data such as the elastic modulus (E), yield stress, ultimate tensile strength, and fracture stress and fracture strain. The elastic modulus was required to calculate fracture properties using CT and SENB tests; it was modified based on the tracking the displacement which resulted in average value of E equal to 1.40 GPa. The mechanical properties obtained using the test is provided in Table 1.

Table 1. Mechanical properties of polyester specimen using simple tension test.

Specimen tag

Yield stress (MPa)

Tensile strength (MPa) Fracture stress (MPa)

Failure strain (%)

Elastic modulus (GPa)

01B10TT 02A10TT 02D10TT 03A10TT

1.351

18.8 18.3 15.7 15.2

18.95 17.78 19.26 17.89 18.47

18.95 17.78 19.26 17.89 18.47

12.81 24.54 24.65 23.95 21.49

1.35 1.51 1.37 1.40

Average values

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6.2. SENB Testing

Thickness Study To ensure the state of plain strain for measuring proper value of fracture toughness, SENB specimen with different thicknesses were used. The cross-head displacement rate was 5mm/min. The force at which the crack propagated was measured and the fracture toughness was calculated using Equation 3. The result of the fracture toughness for different thickness is shown in Fig. 12. The figure shows that a thickness of 15 mm is at least required to obtain a minimum value of fracture toughness. So, the minimum thickness that would ensure the correct value of K is 15 mm thickness. As for the relationship between thickness and fracture toughness, when thickness increases, fracture toughness decreases.

Fig.12: Average thickness vs. average mode I fracture toughness of polyester specimen using SENB test.

The fracture toughness values are calculated based on the measured force at crack opening. The values of some of these forces are shown in Fig. 13 for SENB specimens with different thicknesses.