PSI - Issue 2_A

Philippa Moorea et al. / Procedia Structural Integrity 2 (2016) 3743–3751 Moore & Hutchison/ Structural Integrity Procedia 00 (2016) 000–000

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recent η factor solutions have been published by Ruggieri (2012), which is of a similar form to Canmet but with different coefficients for parent material with strain hardening coefficient (n) of 5 (typical of high strength steel), 10 (which might reflect a structural steel), and 20 (closer to the tensile behaviour of stainless steels). A general form of all these is given in equation 4. These three different approaches were compared by Wang et al (2015), who also offer their own (more complex) approach, where the main coefficients of a 0 /W are defined as θ i χ i , the respective components of which incorporate, the strain hardening coefficient, n, and the B N /W ratio of the specimen, as variables. These different parent material eta functions are plotted in Fig. 1a. Specific η solutions for weld specimens have also been published by Paredes & Ruggieri (2012), for different levels of weld strength mismatch ratio, M y , up to 1.5. An alternative eta factor equation for weld specimens is offered by Moreira & Donato (2010), based on the weld width, 2h, as well as M y , in a twenty-term equation. These eta functions for welds are plotted in Fig. 1b.   i i i W B i CMOD W N e M a                  0 5 0 0.85  (3) When these eta factor functions are plotted against a/W ratio in Fig. 1 it is possible to compare them. The DNV solution (even accounting for the 0.85 factor) is higher than almost all of the others. The Canmet solution is close to other solutions for low levels of strain hardening and/or weld strength overmatch. The Paredes weld equations give significantly lower eta factors than Moreira and Donato, and seem conservative compared to the other solutions. The Wang solutions are close to the Canmet solution within the current a/W range in BS 8571 of 0.2 to 0.5, but diverge beyond this. All the solutions presented here have been individually validated against their own numerical models, so it is not possible to identify from this comparison which is ‘best’ in terms of accuracy. However, the Canmet formula is not an outlier and captures the trend of many of the other solutions, so is a reasonable choice of general eta factor solution for SENT tests. The assumption about eta might need to be further reviewed when testing very high weld strength overmatching (M y > 1.3) or for very high strain hardening materials (n>10). (a) (b)   i i i W t a Coefficien  0 CMOD         0  (4)

Fig. 1. (a) Comparison of plastic eta factors from literature for parent materials with different strain hardening coefficients (n). (b) Comparison of plastic eta factors from literature for welds of different strength mismatch (My) and weld width (2h), alongside the DNV and Canmet formulae.