PSI - Issue 17

Konstantinos Kouzoumis et al. / Procedia Structural Integrity 17 (2019) 347–354 Konstantinos Kouzoumis / Structural Integrity Procedia 00 (2019) 000 – 000

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derived values, however with different accuracy at each level of biaxiality. Comparison between limit load values of analytical equations that concern plates and the tailor made FEA ones cannot be made directly as the geometry of the cruciform specimens affects plastic collapse significantly. The FEA derived Option 3 assessments provide safe results for a conservative definition of K mat . The Option 3 FALs show that for biaxiality ratios lower than one, as biaxiality increases so do the limiting values of K r with increasing L r . This essentially expresses the suppression of plasticity experienced in higher constraint/biaxiality ratios. However, for higher values of biaxiality ( k >1 ) the FAL reaches values of K r higher than one, capturing geometry dependence rather than the biaxiality effect. Following Annex N of BS 7910, constraint corrected Option 3 FALs were generated to account for the change of fracture toughness in relation to constraint. As expected with increasing biaxiality the constraint relaxation was less, leading to the FAL for a biaxiality ratio of k=1 having a minimal change and for k=2 having none at all. For the biaxiality ratios of k=0.5 and k=0 the constraint correction widely increases the safe area below the FAL and non conservative estimates of fracture toughness values provide unsafe results. This suggests that a conservative value of fracture toughness or a high number of tests should follow the use of a more advanced procedure, such as that of Annex N, to ensure safety.

Acknowledgements

This work was made possible by the sponsorship of the industrial members of TWI as part of the Core Research Programme and of the UK Research and Innovation centre. The work was enabled through the National Structural Integrity Research Centre (NSIRC), a postgraduate engineering facility for industry-led research into structural integrity established and managed by TWI through a network of both national and international Universities.

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