PSI - Issue 18

Mehdi Mokhtarishirazabad et al. / Procedia Structural Integrity 18 (2019) 457–471 M. Mokhtarishirazabad / Structural Integrity Procedia 00 (2019) 000–000

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Fig. 9. Force as a function of CMOD for SENB_B20_0.5 samples showing similar responses for sample number 02 and 03. Sample 01 was tested at higher displacement rate and larger displacement intervals. The effect of initial crack length on crack growth resistance of the samples with the thickness B = 20, 10 and 5 mm is illustrated in Fig.10. The standard procedure for converting J Q to J 0.2 is not valid for these specimens, where J 0.2 refers the fracture toughness at 0.2 mm offset form blunting line. Nonetheless, it can be seen that by decreasing the initial crack length (smaller value of a/W ; low in-plane constraint), the critical energy for crack extension is decreased. This finding is in contrast with expected fracture behaviour of ductile materials in tensile type (mode I) fracture and therefore suggests shear type (mode II) fracture is the failure mechanism.

Fig. 10. Fracture surface of plane-sided samples with different thicknesses. Different regions in the fracture surface are marked in the image.

Table 3. Measured crack extension by UC ( Δ a UC ) and fracture surface ( Δ a p ) and estimated values of J Q for samples with the thickness of 10 mm and 5 mm. Sample Thickness (mm) a/W Δ a UC , mm Δ a p , mm Error in estimation of Δ a , % J Q (kJ/m 2 )

SENB_B20_0.5 SENB_B20_0.2 SENB_B10_0.5 SENB_B10_0.2 SENB_B05_0.5 SENB_B05_0.2

20 20 10 10

0.5 0.2 0.5 0.2 0.5 0.2

0.745 2.592 2.944 4.110 3.833 6.614

3.461 4.831 4.877 5.013 5.439 7.063

365

-

86 65 22 42

3651 3072 2489 1697 1288

5 5

7