13th International Conference on Fracture June 16–21, 2013, Beijing, China -9- pure creep damage, pure fatigue damage, creep-fatigue damage and number of cycles to failure are presented in Fig. 5 and 6 for Types 1 and 2 weldments corresponding to εtot = 1% on the outer fiber of remote parent material and t = 5 hours of dwell period. It can be seen that both Types 1 and 2 weldments have the same critical location in the weld toe adjacent to HAZ. In terms of the accumulated total damage at failure, Type 1 weldment has less residual life (N* =142) than Type 2 weldment (N* =223) due to the increased values of parameters characterising hysteresis loop (e.g. total strain range and creep strain, see Figs. 5 and 6). Figure 7. Design contour plot for creep-fatigue durability based on extrapolation of cycles to failure N* and residual life L* The key engineering parameters including the numbers of cycle to failure N* and the residual life L* characterising creep-fatigue durability of the weldment have the principal importance for the design and assessment applications. For the purpose of usability, both parameters N* and L* obtained by LMM calculations and assessments can be represented in the form of design contour plot, shown in Fig. 7 for the Type 2 cruciform weldment. The contour lines (dashed for N* and solid for L*) allows a design engineer to define approximately and rapidly the level of reverse bending moment acceptable for the required service life and assumed average value of dwell period. For a given reverse bending moment and creep dwell period, the numbers of cycle to failure N* and the residual life L* of the cruciform weldment can be approximately estimated from Fig.7. A full discussion of the solutions and further parametric studies are given by Gorash and Chen [14, 15], which demonstrate that, for such complex industrial problems, the LMM is capable of providing lifetime related solutions that are much more illuminating than conventional analysis. 4. Conclusions This paper presents the latest development of the LMM on evaluation of the steady state behavior of an elastic plastic creep body subjected to cyclic loading under high temperature – creep fatigue conditions. The proposed LMM successfully calculates the plastic strain range, the creep stress and accumulated creep strain over a dwell period for a steady state load cycle by an iterative process using a general cyclic minimum theorem. Combining with the experimentally defined creep and fatigue damage data, the final lifetime of the component can then be obtained based on the
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