PSI - Issue 37

7

Cheng Qian et al. / Procedia Structural Integrity 37 (2022) 926–933 Cheng Qian et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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0.2 ( 0.2 ) = 1 + 2

(1) From this analysis, A p was found to have the most promising trend in terms of correlating the X60 pipe steel material’s toughness to constraint level for the current series of tested specimens ( R 2 -values ≥ 0.9, and 0.74 for  J conversion0.2 BL . V p was found to provide the second best given the similar definition with A p . In terms of the stress-based constraint parameters, Q HRR , Q SSY and h showed more promising trends compared to others. Note that current study was only focused on the base metal of an X60 steel pipe. The R -curve of a fracture specimen or real structure is not only affected by geometric constraint induced by dimensions, loading modes and crack sizes, but also material properties such as yield strength and strain hardening, or in the case of weldments, strength mismatch and material inhomogeneity. Further on-going investigations are underway to extend the evaluation to R -curves for X100, X80 and X70 pipe steels to allow for the characterization of strain hardening effect, as well as the characterization of associated weld metals and HAZs.

Fig. 3. Correlation of critical fracture toughness values with constraint parameters.

5. Summary and conclusions Duplicate SE(B) and SE(T) specimens with two different initial crack sizes were prepared from an X60 pipe steel and experimentally tested at room temperature. In general, the results showed the expected trends of higher resistance curves for both shallow-cracked versus deeply-cracked specimen types and tension versus bending loading modes. Eleven constraint parameters (i.e. Q HRR , Q SSY , Q LM , Q BM , A 2 , A 2 BM , h , T z , C p , A p , V p ) were reviewed and calculated based on 3-D FEA. The results and analysis indicated that the shallow-cracked SE(B) specimens exhibited a constraint condition similar to the intrinsically low-constraint deeply-cracked SE(T) specimens. Among all of the evaluated constraint parameters, the A p parameter based on the normalized equivalent plastic strain contour was found to have the most promising trend in terms of co rrelating the material’s toughness to constraint level for currently tested specimens. Further on-going investigations are underway to extend the evaluation to R -curves for X100, X80 and X70 pipe steels to allow for the characterization of strain hardening effect, as well as evaluation of their associated weld metals and HAZs. Acknowledgements The authors are grateful for the X60 pipe steel testing material provided by Dr. Stijn Hertelé at Ghent University. The authors would like to thank Dr. Wenxing Zhou at the University of Western Ontario, Dr. Hari Manoj Simha at the University of Guelph, and Dr. Jia Xue at CanmetMATERIALS for their valuable advice and comments.