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RESEARCH PAPERS

# Modeling of the Behavior of a Welded Joint Subjected to Reverse Bending Moment at High Temperature

[+] Author and Article Information
Alan R. S. Ponter

Department of Engineering, University of Leicester, Leicester, LE1 7RH, UKasp@le.ac.uk

Haofeng Chen

Department of Engineering, University of Leicester, Leicester, LE1 7RH, UK

J. Pressure Vessel Technol 129(2), 254-261 (Jul 14, 2006) (8 pages) doi:10.1115/1.2716429 History: Received February 03, 2006; Revised July 14, 2006

## Abstract

The paper is concerned with the modeling of the behaviour of welds when subjected to severe thermal and mechanical loads where the maximum temperature during dwell periods lies in the creep range. The methodology of the life assessment method R5 is applied where the detailed calculations are carried out using the linear matching method (LMM), with the objective of generating an analytic model. The linear matching method has been developed to allow accurate predictions using the methodology of R5, the UK life assessment method. The method is here applied to a set of weld endurance tests, where reverse bending is interrupted by creep dwell periods. The weld and parent material are both Type 316L(N) material, and data were available for fatigue tests and tests with 1 and $5h$ dwell periods to failure. The elastic, plastic, and creep behavior of the weld geometry is predicted with the LMM using the best available understanding of the properties of the weld and parent material. The numerical results are translated into a semi-analytic model. Using the R5 standard creep/fatigue model, the predicted life of the experimental welds specimens are compared with experimental data. The analysis shows that the most severe conditions occur at the weld/parent material interface, with fatigue damage concentrated predominantly in the parent material, whereas the creep damage occurs predominantly in the weld material. Hence, creep and fatigue damage proceed relatively independently. The predictions of the model are good, except that the reduction in fatigue life due to the presence of the weld is underestimated. This is attributed to the lack of separate fatigue date for the weld and parent material and the lack of information concerning the heat affected zone. With an adjustment of a single factor in the model, the predictions are very good. The analysis in this paper demonstrates that the primary properties of weld structures may be understood through a number of structural parameters, defined by cyclic analysis using the linear matching method and through the choice of appropriate material data. The physical assumptions adopted conform to those of the R5 life assessment procedure. The resulting semi-analytic model provides a more secure method for extrapolation of experimental data than previously available.

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## Figures

Figure 1

Dimensions of the cruciform weld specimens (a) and (b) and schematic of the assumed loading history (c)

Figure 2

(a) Finite element mesh and (b) the shakedown limit interaction curve for weld specimen subjected to cyclic reverse bending moment ΔM and constant bending moment MA

Figure 3

The effective plastic strain range with saturated cycle data with no hold period (a) and maximum effective stress (b) for saturated steady-state cycle ΔM=12.466kNm=1.24ΔMsh. The distribution corresponds to the surface values along the path AB in Fig. 2.

Figure 4

The effective creep strain after 5h hold period (a) and the effective creep stress drop after 5h hold period (b)ΔM=12.466kNm=1.24ΔMsh

Figure 5

Computed variation of the total effective strain range at critical locations and comparison with the analytic solution, Eqs. 15,16,17 remote from the weld

Figure 6

Computed variation of the total strain range at critical locations normalized with respect to the solution remote from the weld

Figure 7

The variation of the maximum stress from the plasticity calculation, the initial creep stress, at critical locations and comparison with the analytic solution, Eq. 19

Figure 8

The variation of the maximum stress from the plasticity, the initial creep stress, calculation at critical locations and normalized with respect to the remote solution, Eq. 20

Figure 9

Variation of the elastic follow-up factor Z with load at critical locations

Figure 10

Comparison between the predictions of the model and experimental failure values, Bretherton (1), for tests conducted at 550°C; (a) direct comparison with the model and (b) the model adapted so that FSRF=1.65

Figure 11

Contours of constant cycles to failure N0*, based upon the analytic model (assuming FSRF=1.65)

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