PSI - Issue 18

Fokion Oikonomidis et al. / Procedia Structural Integrity 18 (2019) 142–162 Dr Fokion Oikonomidis / Structural Integrity Procedia 00 (2019) 000 – 000

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of Table 1. These values can be compared with the estimated K values in the same table (see 3 rd column), at the deepest point of the initially required crack profile (see Fig. 2).

Fig. 28. K values for the fracture test obtained along the front of the crack whose geometry was measured after completion of the test, for three different load values. The effect of residual stresses is not included.

8. Conclusions The post-test metallographic analysis has shown that there was crack growth beyond the fatigue pre-crack front in the test performed. The extensometer, the acoustic emissions outputs, and the metallographic analysis all indicated that crack extension might have taken place during the third constant load. However, there was no quantitative evidence demonstrating at which load the crack extension began, given the relatively small amount of crack extension detected. Taking into account the compressive residual stress at the crack tip, the provisional maximum K value that comes from the second step load of 7035kN is 2735N/mm 1.5 . The average fracture toughness of the material in the same environment measured from small scale testing was 2372 N/mm 1.5 . This value is acceptably near the full-scale value considering the difference in the notch depth ratio, and the design of small-scale specimens having higher constraint, expected to give lower toughness. The results at this stage suggest that small-scale specimens can give conservative predictions of full-scale behaviour of mooring chain links. The results have been used to validate a structural integrity assessment methodology (not covered here) based on fracture mechanics and small scale tests.

Acknowledgements

The authors would like to acknowledge the contribution of all technical personnel in TWI during the testing phase of this project. We would like to thank Mr Fernando Galvan for helping with the Acoustic Emissions measurements and acknowledge the contribution of Veqter Ltd for the Residual Stress measurements.