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Research Papers

Design Evaluation Method for Random Fatigue Based on Spectrum Characteristics

[+] Author and Article Information
Shinsuke Sakai

Department of Mechanical Engineering,  The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, 113-8656 Tokyo, Japansakai@fml.t.u-tokyo.ac.jp

Satoshi Okajima

 Japan Atomic Energy Agency, 4002 Narita, Oarai, Higashi Ibaraki, 311-1393 Ibaraki, Japanokajima.satoshi@jaea.go.jp

Satoshi Izumi

Department of Mechanical Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku,113-8656 Tokyo, Japanizumi@fml.t.u-tokyo.ac.jp

Naoto Kasahara

Department of Nuclear Engineering and Management,  The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, 113-8656 Tokyo, Japankasahara@n.t.u-tokyo.ac.jp

J. Pressure Vessel Technol 134(3), 031204 (May 17, 2012) (5 pages) doi:10.1115/1.4005874 History: Received February 08, 2011; Revised December 09, 2011; Published May 17, 2012

This paper shows a new design approach for random fatigue evaluation based on spectral characteristics. Fatigue damage under random loading is usually evaluated by first, decomposing random waves to stress amplitudes using the rainflow-cycle counting (RFC) method; then, evaluating fatigue damage using Palmgren– Miner’s linear summation rule. In the design process, the fluctuation of load is usually characterized through power spectral density (PSD). Therefore, the design process is expected to be generalized, if the fatigue damage is directly evaluated from the PSD together with the S-N diagram of the material. In fact, many properties related to fatigue damage, such as distribution of extreme values, can be derived theoretically from the geometrical properties of PSD. However, it is rather difficult to derive the distribution of stress amplitude counted by RFC theoretically due to its complicated procedure. In this paper, the upper bound of stress amplitude distribution is confirmed for many random waves generated by numerical simulation for many types of PSDs. Expressing the upper-bound distribution by a closed form function using PSD characteristics leads us to the direct evaluation of fatigue damage with a safety margin if the fatigue damage by a particular stress amplitude is approximated using a series expansion form. A simple procedure for approximating high-cycle fatigue damage for austenitic stainless steel and ferritic steel is proposed in this paper. Finally, a design evaluation procedure based on the fatigue-damage evaluation from PSD together with an S-N diagram is summarized.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

S-N diagram for materials

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Figure 2

Curve fitting for normalized damage γ (material: 2.25Cr-1Mo steel)

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Figure 3

Curve fitting for normalized damage γ (material: 9Cr1Mo steel)

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Figure 4

Curve fitting for normalized damage γ (material: austenitic stainless steel)

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Figure 5

Validation of proposed design procedure

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Figure 6

Geometries of S(ω)

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Figure 7

Cumulative distribution of RFC range

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Figure 8

ɛ  − r relation: (a) 2.25Cr-1Mo steel, (b) 9Cr1Mo steel, and (c) austenitic stainless steel

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