PSI - Issue 13

Wei Song et al. / Procedia Structural Integrity 13 (2018) 2227–2232 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

2232

6

were reanalyzed based on these equations. The resulting effective notch strain range estimated from analytical equations considering the geometry penetration and material mismatch effects was plotted against the fatigue test data, as shown in Fig. 8(b). From the comparison between the proposed fatigue prediction equation and fatigue life results, nearly all of prediction data are along with the 97.7% survival probability. Therefore, the proposed equations can be used to evaluate the weld root failure of CLWJ with the different penetration and mismatch effect for low and high cycle fatigue. However, these analytical equations cannot estimate the notch effective strain at weld toe. It should be further developed corresponding notch characteristic equations for fatigue comprehensive assessment of CLWJ. (a) 1  10 -2 (b) -1

2100

3*10

0.7 0.5 0.3 0.2

h

h

T

ension t

Tension

p

10 -1

p

1050

t

L

L R=0.

1

failu

Wel

d root .18

re

0.1 Nominal stain range  n (mm/mm) 0.07 0.05 0.03 0.02 UM F HC F LC

10 -2 Nominal stress range (MPa) Notch stain range  eff (mm/mm) 10 -3 LCF M HCF M E U

313

N ) -0. f

 eff = 0 

47  (

210

EM

P s

%]

P ratio=0.7 (WT) rati WR) o=0 ( rati WR) P T) o=0.5 (W P P o=0.5 ( rati

[97.7

105

rati P

o=0.5

P ratio=0 P ratio=0

ratio=0.7 ( ratio=0 ( )

P P

WT) WR

21

0.01

10 -4

10 2

10 3

10 4

10 5

10 6

10 7

10 1

10 2

10 3

10 4

10 5

10 6

10 7

Cycles to failure N f Cycles to failure N f Fig. 8 Low and high fatigue life assessment using nominal strain concept and effective notch strain concept.

4. Conclusion The low and high cycle fatigue assessment by nominal strain concept, and effective notch strain concept, performed in the study considering the weld root penetration length and material yield stress mismatch between base metal and weldments. (1) Material strength heterogeneity and the weld geometry variations have great influenced on low cycle fatigue. (2) The fatigue strength of 10NiCr3MoV steel load-carrying cruciform joints for low cycle fatigue can be assessed by FAT 160 (k=5) including weld toe and weld root failure. (3) The analytical equations of effective notch strain are valid for estimating weld root strain for low and high cycle fatigue life assessment. References Dong .P, Cao .Z, Hong J.K., Low-cycle fatigue evaluation using the weld master S-N curve, in: American Society of Mechanical Engineers, Pressure Vessels and Piping Division (Publication) PVP, 2006. Möller B., Baumgartner J., Wagener R., Kaufmann H., Melz T., Low cycle fatigue life assessment of welded high -strength structural steels based on nominal and local design concepts, Int. J. Fatigue 101 (2017) 192-208. Nykänen T., Mettänen H., Björk T., Ahola T., Fatigue assessment of welded joints under variable amplitude loading using a novel notch stress approach, Int. J. Fatigue 101 (2017) 177-191. Pei X., Wang W., Dong P., An Analytical-Based Structural Strain Method for Low Cycle Fatigue Evaluation of Girth-Welded Pipes, (2017) V03BT03A015. Radaj D., Sonsino C.M., Fricke W., Recent developments in local concepts of fatigue assessment of welded joints, Int. J. Fatigue 31 (2009) 2-11. Radaj D., Fricke W., Fatigue assessment of welded joints by local approaches, Cambridge England, 2006. Saiprasertkit K., Hanji T., Miki C., Fatigue strength assessment of load-carrying cruciform joints with material mismatching in low- and high- cycle fatigue regions based on the effective notch concept, Int. J. Fatigue 40 (2012) 120-128. Saiprasertkit K., Hanji T., Miki C., Local strain estimation method for low- and high-cycle fatigue strength evaluation, Int. J. Fatigue 40 (2012) 1- 6. Saiprasertkit K., Sasaki E., Miki C., Fatigue crack initiation point of load carrying cruciform joints in low and high cycle fatigue regions, Int. J. Fatigue 59 (2014) 153-158.