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Research Papers: Materials and Fabrication

Comparison and Assessment of the Creep-Fatigue Evaluation Methods With Notched Specimen Made of Mod.9Cr-1Mo Steel

[+] Author and Article Information
Masanori Ando, Nobuchika Kawasaki

Japan Atomic Energy Agency,
4002 Narita,
Oarai, Ibaraki 311-1393, Japan

Yuichi Hirose

Mitsubishi Heavy Industry, Ltd.,
5-717-1 Fukahori,
Nagasaki, Nagasaki 851-0392, Japan

Takanori Karato

Mitsubishi Heavy Industry, Ltd.,
2-1-1 Shinhama, Arai,
Takasago, Hyogo 676-8686, Japan

Sota Watanabe

Mitsubishi Heavy Industry, Ltd.,
1-1-1 Wadamisaki, Hyogo,
Kobe, Hyogo 652-8585, Japan

Osamu Inoue

IX Knowledge, Inc.,
4002 Narita,
Oarai, Ibaraki 311-1393, Japan

Yasuhiro Enuma

Mitsubishi FBR Systems, Inc.,
2-34-17, Jingumae,
Shibuya, Tokyo 150-0001, Japan

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received November 27, 2012; final manuscript received January 22, 2014; published online April 16, 2014. Assoc. Editor: Osamu Watanabe.

J. Pressure Vessel Technol 136(4), 041406 (Apr 16, 2014) (10 pages) Paper No: PVT-12-1178; doi: 10.1115/1.4026852 History: Received November 27, 2012; Revised January 22, 2014

In components design at elevated temperature, creep-fatigue is one of the most important failure modes, and assessment of creep-fatigue life in structural discontinuities is an important issue in evaluating the integrity of components. Therefore, a lot of creep-fatigue life evaluation methods were proposed until now. To compare and assess the evaluation methods, a series of creep-fatigue test was carried out with notched specimens. All the specimens were made of Mod.9Cr-1Mo steel, which is a candidate material for primary and secondary heat transport system components of the Japan sodium-cooled fast reactor (JSFR). Mechanical creep-fatigue tests and thermal creep-fatigue test were performed by using a conventional uni-axial push–pull fatigue test machine and a thermal gradient generating system with an induction heating. The stress concentration levels were adjusted by varying the notch radius in the each test. The creep-fatigue lives, crack initiation, and propagation processes were monitored by a digital microscope and the replica method. A series of finite element analysis (FEA) was carried out to predict the number of cycles to failure by the several creep-fatigue life evaluation methods. Then, these predictions were compared with the test results. Several types of evaluation methods such are stress redistribution locus (SRL) method, simple elastic follow-up method and the methods described in the design and constriction code for fast reactor (FR) published by the Japan Society of Mechanical Engineers (JSME FRs code) were applied. Through the comparisons, it was appeared that SRL method gave rational conservative prediction of the creep-fatigue life when the factor of κ = 1.6 was applied for all conditions tested in this study. A comparison of SRL method and simple elastic follow-up method indicated that SRL method applied factor of κ = 1.6 gave the smallest creep-fatigue life in practicable stress range level. The JSME FRs code gave an evaluation 70–100 times conservative lives comparing with the test results.

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Figures

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Fig. 1

Evaluation procedure of creep-fatigue life on the assumption of fully cyclic test

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Fig. 2

The average fatigue curve and reduced fatigue curve [25,31]

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Fig. 3

Configuration of the notched bar specimens

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Fig. 4

Configuration of the notched plate specimen and overview of the thermal gradient measurement test

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Fig. 5

Measurement results of thermal gradient history in the notched plate specimen

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Fig. 6

FEA models used in this study: (a) The sector model of a notched bar specimen (ρ = 11.6 mm) and (b) The sector model of a notched plate specimen (R = 5 mm)

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Fig. 7

Observed results of the longest cracks on the surface of the notch roots in the creep-fatigue test with notched bar specimens

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Fig. 8

Comparison of the creep-fatigue lives between the experimental results of N25%drop and predicted results by average fatigue curve in the creep-fatigue test with notched bar specimens

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Fig. 9

Procedure of the experimental base evaluation

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Fig. 16

Relationship between peak stress by elastic FEA and the number of cycles predicted by each method in the creep-fatigue condition of 550 °C—0.5 h tension hold.

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Fig. 15

Estimated stress and strain behavior by each method in the creep-fatigue test with notched bar specimen of ρ = 1.6 mm

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Fig. 17

Relationship between the number of cycles predicted by each method and holding time for each peak stress level at 550 °C

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Fig. 14

Accumulated damages at the failure cycles estimated by each method for the testing of notched plate specimen

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Fig. 13

Comparison of the experimental and predicted results of N1mm in the creep-fatigue test with notched plate specimen

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Fig. 12

Experimental results of the longest crack growth on the surface of the notch roots in the creep-fatigue test with notched plate specimen

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Fig. 11

Accumulated damages at N1mm estimated by each method in the creep-fatigue test with notched bar specimens

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Fig. 10

Comparison of the number of cycles to failure between experimental results of N1mm and predicted results by reduced curve in the creep-fatigue test with notched bar specimens

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Fig. 18

Scheme of the SRL method

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