PSI - Issue 18

461 5

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

Fig. 5. CT specimen deformation during the test. Plastically deformed areas are marked by dashed lines.

3.3. Fracture of plane sided SENB specimen Fig. 10 shows the sequences of sample surface deformation from zero load to maximum load for SENB_B20_0.5_3. Significant crack tip blunting can be seen before stable tearing at the tip of EDM slit occurs. Such blunting behaviour suggests that a 0.1 mm EDM notch can work like a fatigue pre-crack, eliminating the time consuming stage of sample preparation.

Fig. 6. Extensive crack tip blunting before crack propagation at the surface of the SENB_B20_0.5 sample.

The load as a function of the CMOD for samples with thicknesses of 5, 10 and 20 mm with the a/W = 0.5 and 0.2 are shown in Fig. 7. It can be seen that the maximum load for samples with shorter crack length was higher than larger cracks while CMOD is less for samples with shorter cracks rather larger cracks at maximum load. For all specimens, the resistance curve was plotted following ASTM standard. It worth noting that the ASTM equation for plotting the blunting line is valid for most materials. However, in case of low strength materials with high strain hardening capability such as austenitic stainless steels, using this equation leads to overestimating the fracture toughness of the material (Mills 1997). To address this issue, the theoretical blunting line is plotted using the following equation (Landes 1995): � � � � ��� � �� (1) where M = 3.75 for stainless steel 316 (Landes 1995) and σ uts is the ultimate tensile strength of the material.