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Research Papers: Design and Analysis

Study on Dynamic Strength Evaluation Method of Mechanical Members Based on Energy Balance

[+] Author and Article Information
Keisuke Minagawa

Department of Mechanical Engineering, Tokyo Denki University, 2-2 Kanda-Nishiki-cho, Chiyoda-ku, Tokyo 101-8457, Japanminagawa@cck.dendai.ac.jp

Satoshi Fujita

Department of Mechanical Engineering, Tokyo Denki University, 2-2 Kanda-Nishiki-cho, Chiyoda-ku, Tokyo 101-8457, Japansfujita@cck.dendai.ac.jp

Seiji Kitamura

Advanced Nuclear System R&D Directorate, Japan Atomic Energy Agency, 4002, Narita, O-arai, Higashiibaraki-gun, Ibaraki, 311-1393, Japankitamura.seiji@jaea.go.jp

Shigeki Okamura1

Advanced Nuclear System R&D Directorate, Japan Atomic Energy Agency, 4002, Narita, O-arai, Higashiibaraki-gun, Ibaraki, 311-1393, Japanokamura.shigeki06@jaea.go.jpf

1

Present address: Mitsubishi FBR Systems, 2-34-17, Jingumae, Shibuya-ku, Tokyo, 150-0001, Japan.

J. Pressure Vessel Technol 131(3), 031205 (Apr 13, 2009) (6 pages) doi:10.1115/1.3109990 History: Received November 05, 2007; Revised September 22, 2008; Published April 13, 2009

In Japan, mechanical structures installed in nuclear power plants, such as piping and equipment, are usually designed statically in an elastic region. Although these mechanical structures have sufficient seismic safety margin, understanding the ultimate fatigue endurance is very important in order to improve the seismic safety reliability for unexpected severe earthquakes. Moreover, clarifying a margin of seismic resistance of mechanical structures that suffered a severe earthquake is being required. In this study, the energy balance equation that is one of valid methods for structural calculation is applied to the above-mentioned issues. The main feature of the energy balance equation is that it explains accumulated information of motion. Therefore the energy balance is adequate for the investigation of the influence of cumulative load such as seismic response. The investigation is implemented by forced vibration experiments. The experiment models are simple single–degree-of-freedom models that are made of stainless steel and carbon steel. In the experiment, random waves having predominant frequency similar to natural frequency of the experimental model are input in order to obtain adequate response not only in the elastic region but also in the plastic region. As a result, experimental models vibrate under resonance condition, so response acceleration is approximately seven times as big as the input. The excitation is continued until the experimental models fracture, and is carried out with various input levels. In the experiment, models suffered cracks at the bottom end, and fractured finally. As a result, input energy for failure increases as time for failure. In other words, more input energy for failure is needed in case of small input. Moreover the correlation between increment in input energy and input energy for failure is investigated. It was confirmed that input energy for failure is inversely proportional to increment in input energy per unit time. Additionally energy for failure of stainless steel is about twice as big as carbon steel. The correlation between fatigue failure and energy is confirmed from the vibration experiment. Therefore it is expected that time for fatigue failure can be evaluated by the energy balance equation.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Single degree of freedom model

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Figure 2

Experimental models

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Figure 3

Shaking table with experimental model

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Figure 4

Time histories of fatigue failure vibration experiment (stainless steel, 0.130 m, 15.2 Hz, and Wave 2)

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Figure 5

Changes in response (stainless steel, 0.130 m, 15.2 Hz, and Wave 2)

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Figure 6

Changes in response (carbon steel, 0.130 m, 15.4 Hz, and Wave 2)

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Figure 7

Time and input energy for failure (stainless steel)

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Figure 8

Time and input energy for failure (carbon steel)

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Figure 9

Increment in input energy and input energy for failure (stainless steel, 0.130 m, and 15.2 Hz)

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Figure 10

Increment in input energy and input energy for failure (carbon steel, 0.130 m, and 15.4 Hz)

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Figure 11

Maximum input acceleration and input energy for failure (stainless steel, 0.130 m, and 15.2 Hz)

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Figure 12

Maximum input acceleration and input energy for failure (carbon steel, 0.130 m, and 15.4 Hz)

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