PSI - Issue 13

Mihaela Iordachescu et al. / Procedia Structural Integrity 13 (2018) 554–559 M. Iordachescu, A. Valiente, E. Scutelnicu/ Structural Integrity Procedia 00 (2018) 000–000

559

6

There is no difference between the two tests conducted with CTs in the HAZ of RWs concerning σ Y , although its value increases with the specimen deformation. In this case, it is not possible to contrast the σ Y variation with the strain hardening capacity, since the true stress-strain curve of the HAZ is not known. The moment-rotation diagrams M-Θ were obtained from the Eq. (1), Eq. (3) and Eq. (4) and, the experimental values of a, δ and F. These diagrams describe the behavior of a plastic hinge as determined by the strength and ductility of the cracked ligament contained into the joint HAZ. Fig. 3c shows the diagrams of all fracture tests in terms of the relative moment: where M(0) is the moment for which the fully plastic yielding of the CT specimen takes place. Given that M(0) is mainly determined by the yield strength, the total moment M was replaced by the moment ratio of Eq. (5) in order to assess the influences of yield strength and strain hardening separately. The diagrams provided in Fig. 3c show the rotation capacity of the specimen once the resistant ligament is plastically collapsed and the crack growth occurs. The main effect concerning the weld quality that these diagrams underline is the plastic deformation increase required by ductile fracture initiation and growth, as a consequence of the strain hardening capacity retained by the welded joint. Despite the significant dispersion shown by the test results, even in the case of a homogeneous the material such as BM, they indicate improved rotation capacity of CT specimens containing RW when compared with that with NW, especially after the maximum rotation moment is reached and the ductile fracture of HAZ initiates. 4. Conclusions The comparison method employed to determine the effectiveness of a repairing technique for welded joints made of a constructional steel allow the bearing capacity and the joints deformability to be assessed regarding their contribution to the overall structural compliance. The method goes beyond the standardized procedures of Fracture Mechanics, since it has been devised to analyze results of fracture tests performed with precracked CT specimens when fully plastic regime prevails. The structural performance of welds in as-designed and repaired condition can be quantitatively compared through the moment-rotation diagrams of CT specimens with the fatigue crack contained in the HAZ of the welded joints. Comparison can be extended to base metal as overall benchmark of the welded joints. The diagrams are obtained from the fracture testing results on the basis of a plane stress plastic collapse model of the cracked CT specimens, which takes into account ductile crack growth. The influences of strain hardening capacity and ductile fracture resistance on the moment-rotation diagrams can be separated from that of yield strength. The particular application of the method performed here confirms the better behavior of the base metal when comparing it with the HAZs of the tested joints and shows that joint performance improves by repairing. References ASTM E-1820, Standard Test Method for Measurement of Fracture Toughness, ASTM International, 2015 EN 1993-1-8:2005, Eurocode 3: Design of steel structures - Part 1-8: Design of joints EN 1993-1-9:2005, Eurocde 3: Design of steel structures - Part 1-9: Fatigue Hu, J.M, Albrecht, P., Limit load solutions and loading behavior of C(T) fracture specimens, International Journal of Fracture, 1991, 52, 19-45 Kachanov, L. M., Fundamentals of the Theory of Plasticity, Dover Publications, Mineola N.Y., 2004 Kumar, V., German, M.D., Shih, S.F., An Engineering Approach for Elastic–Plastic Fracture Analysis, NP-1931, Electric Power Research Institute, 1981 Spanish Code for Structural Steel (EAE), Ministry of Development, Madrid, 2011, ISBN: 978-84-498-0904-0   M  M/M(0) (5)