13th International Conference on Fracture June 16–21, 2013, Beijing, China 3 with lower strength and plasticity in tensile test, the CG-specimen exhibits a high resistance to crack extension in Charpy V test, is analyzed in following two paragraphs. 700 800 900 1000 1100 1200 1300 1400 62 64 66 68 70 72 74 76 RT 1320 730 900 σy ψ(%) T(℃) σy (σ b ), MPa 母材 600 ψ σ b 700 800 900 1000 1100 1200 1300 1400 62 64 66 68 70 72 74 76 -50℃ 1320 730 900 σy ψ(%) T(℃) σy (σ b ), MPa 母材 600 ψ σ b (a) (b) Fig. 1 Results of tensile tests at RT and at -50℃ (a) Specimen ,1320℃ (b) Specimen, 900℃ (c) Specimen ,1320℃ (d) Specimen, 900℃ (e) Specimen, 900℃ Fig. 2 Microstructures of simulated CGHAZ and FGHAZ specimen 0 50 100 150 200 Ei Ep Et 1320 730 900 T(℃) 母材 600 Ei,Ep,Et (J) RT 0 50 100 150 200 Ei Ep Et 1320 730 900 T(℃) 母材 600 Ei,Ep,Et (J) -50℃ 20 40 60 80 100 120 140 160 180 200 Ei Ep 1320+900 1320+1320 1320+730 900+1320 T(℃) 900+730 900+900 Ei,Ep,Et (J) RT Et Fig. 3 The results of Charpy V tests at RT and at -50℃ 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 0 5 10 15 20 25 30 35 P,KN X,mm 1320℃ 900℃ 730℃ 600℃ base metal RT 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 0 5 10 15 20 25 30 35 P,KN X,mm 1320℃ 900℃ 1320+1320℃ 900+900℃ RT Fig. 4 Load-displacement plots measured by the instrumented impact machine(a) specimens by single heating (b) Comparison of effects of single and double heating 3.2 Different micro-mechanisms of rupture for CG-specimen and FG-specimen. Fig. 5(a) shows the fracture surfaces of Charpy V specimen of CG. It is apparent that the ductile rupture is caused by the primary voids, which nucleate, grow until impingement-resulting coalescence and final rupture. In this case the rupture obeys the criterion of critical void growth. According to the void growth model of Rice and Tracey [7]: 714nm 500nm 370nm B
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