PSI - Issue 68

Josef Arthur Schönherr et al. / Procedia Structural Integrity 68 (2025) 425–431 J. A. Scho¨nherr et al. / Structural Integrity Procedia 00 (2024) 000–000

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Fig. 2. Meshed finite element simulation model with a crack in the interface between ICCHAZ B and the buttering layer. The material regions are di ff erentiated by their color.

3. Simulation model

The ASTM E1457 method, the Abaqus integral method and the dissipated creep stress power method are compared regarding their performance in calculating C ∗ for multi-layer welded joints by means of finite element simulations. The simulation model is based on a compact-tension specimen extracted from a welded joint made from the steels X10CrWMoVNb9-2 (P92) and GX13CrMoCoVNbNB9-2-1 (CB2) with an additional buttering layer. Each of the three heat a ff ected zones (enumerated as A, B and C) is subdivided into an ICHAZ, FGHAZ and CGHAZ sub-zone adding up to thirteen individual regions, Fig. 2. The creep properties of the individual zones are considered by dividing each HAZ into three distinct zones with individual Norton creep model parameters. These are derived based on creep test data obtained from microstructurally simulated specimens, generated by Fehe´r (2014). Since the contour integral method to calculate C ∗ as well as the ASTM E1457 method are not strictly applicable to be used in this multi-material analysis and furthermore, the ASTM E1457 method is limited to a common Norton exponent n , additional material model parametrizations are introduced. Firstly, the simulations are carried on a ho mogeneous material specimen, Fig. 3 (a), secondly the Norton models were fitted such as n is equal for each region, Fig. 3 (b), and lastly, n is determined individually for each region, Fig. 3 (c). In the latter, the creep properties of the particular zones di ff er momentously. For the Abaqus integral method, results for a total of twelve contours are requested as output variables. Like exemplified in the manual, the results for contours two to twelve are as well fitted using a second order polynomial in order to extrapolate the C t value to the very crack tip. The ASTM E1457 method results were calculated using n corresponding to the region above the crack tip. For the dissipated creep power method, the F vs. ˙ v cr curves are generated with 50 support points distributed over the interval of [0 , F ] each, adding up to a total of 100 simulations per crack location and material parameter set.

4. Results and Discussion

Di ff ering material parameters per region results in an unsymmetric deformation of the specimen in conjunction with a partly discontinuous stress distribution. This holds particularly true for the material parameter set, where A and n are determined independently per region, Fig. 4. In Fig. 5, the C ∗ results for each of the three material parameter sets, see Fig. 3, for a crack in between ICHAZ B and the buttering layer are plotted, normalized with the results of the dissipated creep stress power results. For the homogeneous specimen as well as for the material parameter set with equal Norton exponent n , the results only vary slightly. If both A and n are determined per region, both, the