PSI - Issue 13

Atsuhisa Kitade et al. / Procedia Structural Integrity 13 (2018) 1845–1854 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

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Cowper-Symonds equation (4) was used for fitting, but in actual experiments the results were scattered and stable results could not be obtained, so based on the values of [Kawabata et al. 2012], the coefficient was determined to be 2 for 5 × 10 4 for C and 4.854 for P . p y y0 1 n         = +     (3)

1

   

   

˙     C    p 1 +             p

n

  

   



p

y0 1  =  +

(4)

 

y



The critical principal stress, which is the criterion of brittle fracture, is estimated originally from the microstructure using the discussion in Chapter 2, but in this chapter, the critical main stress is obtained by separately performing a double notch test for model development, σ = 2205MPa.

Fig.18 Analysis result when changing G c

For the critical strain which is the ductile fracture criterion, the value was determined with reference to the shape of the specimen after the experiment. If the critical strain is increased, more strain will be accumulated before brittle fracture, and deformation of the specimen will be greater. As shown in Fig.17, using the ratio of the length of the upper end portion of the test piece and the length of the central portion, or the ratio of the length of the lower end portion to the length of the central portion after the experiment, the critical strain 0.24 was specified. Since the dissipated energy G c at the time of brittle fracture could not be determined by experiments, it can be utilized as a fitting parameter and change the dissipated energy value to see whether the temperature transition can be correctly expressed. Fig. 18 is an analysis of whether the transitions at two temperatures of -40 ° C and 0 °C can be expressed correctly when the dissipated energy G c is changed. In the analysis of Fig.18, analysis was not conducted until the end of fracture, but only whether brittle fracture occurred at first was investigated. As can be seen from Fig. 18, when the value of G c is increased, since more energy is absorbed during brittle fracture, there is a high possibility that brittle fracture will not continue. When G c was 45000 J/ 2 , a brittle fracture surface appeared mostly even at 0 ° C, whereas when G c was raised to 55000 J/ 2 , it also became a ductile fracture surface 3.3. Analysis result