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Research Papers: Materials and Fabrication

The Sensitivity to the Lode Parameter in Ductile Failure of Tubular Steel Grades

[+] Author and Article Information
I. Barsoum

Department of Mechanical Engineering,
The Petroleum Institute,
Khalifa University of Science and Technology,
P.O. Box 2533,
Abu Dhabi, United Arab Emirates
e-mail: ibarsoum@pi.ac.ae

M. A. Al-Khaled

Department of Mechanical Engineering,
The Petroleum Institute,
Khalifa University of Science and Technology,
P.O. Box 2533,
Abu Dhabi, United Arab Emirates

1Corresponding author.

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received October 29, 2017; final manuscript received January 29, 2018; published online April 4, 2018. Assoc. Editor: Kiminobu Hojo.

J. Pressure Vessel Technol 140(3), 031402 (Apr 04, 2018) (9 pages) Paper No: PVT-17-1218; doi: 10.1115/1.4039392 History: Received October 29, 2017; Revised January 29, 2018

Ductile failure in steels is highly controlled by the stress state, characterized by the stress triaxiality (T) and the Lode parameter (L). The ASME Boiler and Pressure Vessel Code requires pressure vessels to be designed to resist local ductile failure. However, the standard does not account for the Lode parameter dependence in its failure locus. In this study, the influence of the stress state, characterized T and L, on the ductility of ASME tubular product steel grades is investigated. Two seamless pipes of midstrength carbon steel SA-106 Gr. B and high-strength superduplex steel SA-790 were considered. Ring specimen geometries for plane strain (PS) stress state (L = 0) and tensile stress (TS) state (L = −1) are utilized to establish the ductile failure locus in terms of T and L for the two steels. The experimental results (EXP) show that the effect of the Lode parameter on the failure locus for the SA-106 Gr. B steel is insignificant, whereas for the SA-790 steel, the effect is rather significant. A parameter SL is introduced in order to quantify the sensitivity of the failure locus to the Lode parameter. It is found that for materials with ultimate strength lower than about 550 MPa, the sensitivity to L is insignificant (SL ≈ 1), whereas for materials with ultimate strength higher than 550 MPa, the sensitivity to L could be significant (SL > 1). Scanning electron microscopic (SEM) analysis of the fracture surfaces revealed that the sensitivity to L is closely associated with the rupture micromechanisms involved.

Copyright © 2018 by ASME
Topics: Steel , Stress , Failure
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References

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Figures

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Fig. 1

True stress–strain curves for SA-106 Gr. B and SA-790 steel

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Fig. 2

Ring specimens: (a) SA-106 TS, (b) SA-790 TS, (c) SA-106 PS, and (d) SA-790 PS

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Fig. 3

Cross section of the: (a) TS and (b) PS specimen

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Fig. 4

Reaction force (F) versus D-block displacement (δ) and stress triaxiality and the Lode parameter path plots through net-section thickness (ξ) and width (η) for SA-106 and SA-790 steel with 3 mm notch radius

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Fig. 5

Experimental setup: (a) fixture and ring specimen and (b) target point for measuring strain

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Fig. 6

Comparison of force F versus strain e25 between experiment and FEA for SA-790 steel

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Fig. 7

Stress triaxiality (T) versus equivalent plastic strain (εp) with experimental failure results for: (a) TS (L = −1) SA-106, (b) PS (L = 0) SA-106, (c) TS (L = −1) SA-790, and (d) PS (L = 0) SA-790

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Fig. 8

Failure locus for all SA-106 specimens including uniaxial specimens, TS and PS ring specimens with the ASME-BPVC failure locus [16]

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Fig. 9

Failure locus for all SA-790 specimens including uniaxial specimens, TS and PS ring specimens with the ASME-BPVC failure locus [16]

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Fig. 10

Lode sensitivity parameter (LS) versus material yield strength (Sy) for SA-106, SA-790 and other materials in the literature

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Fig. 11

Lode sensitivity parameter (LS) versus material ultimate strength (Sut) for SA-106, SA-790 and other materials in the literature

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Fig. 12

Lode sensitivity parameter (LS) versus material R-ratio (Sy/Sut) for SA-106, SA-790 and other materials in the literature

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Fig. 13

SEM fractographs of SA-106 low stress triaxiality levels with notch radius ρ = 24 mm: (a) TS (L = −1) with T¯=0.5 and (b) PS (L = 0) with T¯=0.6

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Fig. 14

SEM fractographs of SA-790 high stress triaxiality levels with notch radius ρ = 1 mm: (a) TS (L = −1) with T¯=1.2 and (b) PS (L = 0) with T¯=1.0

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Fig. 15

Macroscopic SEM fractographs at high triaxiality level for PS specimens (ρ = 1 mm): (a) SA-106, PS with T¯=0.9 and (b) SA-790, PS with T¯=1.0

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