PSI - Issue 13

Taiko Aikawa et al. / Procedia Structural Integrity 13 (2018) 104–109 Aikawa/ Structural Integrity Procedia 00 (2018) 000 – 000

108

5

thickness than near the plate surfaces. This is because the plane strain condition is maintained near the mid-thickness while it is lost near the plate surfaces. This result might have been influenced by the fact that the crack closure effect by uncracked ligament is stronger near the plate surfaces and the crack is less likely to satisfy the fracture condition, Eq. (1), see dotted line in Fig.4. 4.2. Example calculations Figure 7 shows example calculations for temperature-gradient crack arrest test. The same testing conditions as Fig.5 is applied but Charpy absorbed energy transition temperature was changed as -50 ℃ , -75 ℃ and -100 ℃ . Calculated crack arrest length decreased as steel toughness increased. From this result, the model proposed by the present study can reproduce actual crack propagation and arrest process together with fracture surface morphologies. The model is expected to use for understanding the relationship between crack arrest toughness and fracture surface morphologies.

Fig.7 Calculated fracture surface, (a) = −50℃ , (b) = −75℃ , (c) = −100℃ .

5. Conclusions

A computer simulation model has been developed to reproduce brittle fracture surface morphologies. Local stress intensity factor along propagating crack front is calculated considering the fracture surface irregularity and crack front non-straightness. Crack closure stress by uncracked ligament is also taken into consideration in calculating the local stress intensity factor. The local stress intensity factor is compared with assumed critical value to judge crack propagation and arrest at each crack front location. The present model was applied to wide-plate crack arrest tests with temperature-gradient and it was shown that fracture surface morphologies including shear-lip formation, crack-front tunneling and chevron markings were well reproduced by the present model. The present model is expected to use for understanding the relationship between crack arrest toughness and fracture surface morphologies in steel plates.

Acknowledgements The present study was supported by JSPS KAKENHI grant Number 17H01354, Japan.

References Aikawa T., 2018., Master thesis, The University of Tokyo, March 2018. Aihara S. and Tanaka Y., 2011. Acta Materialia 59, 4641-4652.