Experimental and numerical study on the relationship between creep crack growth properties and fracture mechanisms

Most heat resisting materials in structural components are used under multi-axial stress conditions and under such conditions ductile materials often exhibit brittle manner and low creep ductility at elevated temperature. Creep crack initiation and growth properties are also affected by multi-axial stress and it is important to evaluate these effects when laboratory data are applied to structural components. Creep crack growth tests using circumferential notched round bar specimens are a simple method to investigate multi-axial stress effects without using complicated test facilities. Creep crack growth tests have been performed using a 12CrWCoB turbine rotor steel. In order to investigate the effects of multi-axial stress on creep crack growth properties, the tests were conducted for various notch depths at 650°C. The circumferential notched round bar specimen showed brittle crack growth behaviour under multi-axial stress conditions. Creep crack growth rate was characterized in terms of the C* parameter. A 12CrWCoB turbine rotor steel has been tested using circumferential notched round bar specimens with different multi-axiality. Circumferential notched round bar specimens show increased brittle creep crack growth behaviour due to the multi-axial stress condition. Creep crack growth properties could be predicted by allowing for the decrease of creep ductility under multi-axial conditions.

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Creep Crack Growth Test Method and Creep Crack Growth Properties for TiAl Intermetallic Compound.

Journal of the Society of Materials Science Japan ◽

10.2472/jsms.49.80 ◽

2000 ◽

Vol 49 (1) ◽

pp. 80-85 ◽

Cited By ~ 1

Author(s):

Masaaki TABUCHI ◽

Toshimitu YOKOBORI ◽

Akio FUJI ◽

Kiyoshi KUBO ◽

Koichi YAGI ◽

...

Keyword(s):

Intermetallic Compound ◽

Crack Growth ◽

Creep Crack Growth ◽

Test Method ◽

Creep Crack ◽

Growth Test ◽

Tial Intermetallic Compound ◽

Growth Properties

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Estimation of Creep Crack Growth Properties Using Circumferential Notched Round Bar Specimen for 12CrWCoB Rotor Steel

Key Engineering Materials - Advances in Fracture and Strength ◽

10.4028/0-87849-978-4.397 ◽

2005 ◽

pp. 397-402

Author(s):

Je Chang Ha ◽

Joon Hyun Lee ◽

Tabuchi Masaaki ◽

A.Toshimitsu Yokobori

Keyword(s):

Crack Growth ◽

Creep Crack Growth ◽

Rotor Steel ◽

Creep Crack ◽

Round Bar ◽

Growth Properties

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Creep crack growth properties for 12CrWCoB rotor steel using circular notched specimens

International Journal of Pressure Vessels and Piping ◽

10.1016/j.ijpvp.2004.03.011 ◽

2004 ◽

Vol 81 (5) ◽

pp. 401-407 ◽

Cited By ~ 19

Author(s):

Jechang Ha ◽

Masaaki Tabuchi ◽

Hiromichi Hongo ◽

A. Toshimitsu Yokobori ◽

Akio Fuji

Keyword(s):

Crack Growth ◽

Creep Crack Growth ◽

Rotor Steel ◽

Creep Crack ◽

Notched Specimens ◽

Growth Properties

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Effect of carbon content and helium gas environment on creep crack growth properties of Ni-26 pct Cr-17 pct W-0.5 pct Mo alloy at 1273 K

Metallurgical and Materials Transactions A ◽

10.1007/bf02664674 ◽

1995 ◽

Vol 26 (2) ◽

pp. 383-389 ◽

Cited By ~ 2

Author(s):

Masaaki Tabuchi ◽

Yuji Nakasone ◽

Toshio Ohba ◽

Koichi Yagi ◽

Tatsuhiko Tanabe

Keyword(s):

Carbon Content ◽

Crack Growth ◽

Creep Crack Growth ◽

Creep Crack ◽

Helium Gas ◽

Growth Properties ◽

Gas Environment

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The Influence of Metallurgical and Mechanical Pre-Damage on Creep-Crack and Fatigue-Crack Growth Rates of CrMoV Steel

Volume 4: Turbo Expo 2004 ◽

10.1115/gt2004-53399 ◽

2004 ◽

Author(s):

Masaru Sekihara ◽

Shigeo Sakurai

Keyword(s):

Stress Intensity Factor ◽

Fatigue Crack ◽

Fatigue Crack Growth ◽

Crack Growth ◽

Growth Rates ◽

Creep Crack Growth ◽

Creep Crack ◽

The Relationship ◽

Crack Growth Rates

The effects of mechanical degradation on the creep- and fatigue-crack growth rates in power plants operated long-term were studied. Creep-crack growth tests and fatigue-crack growth tests were performed using creep-pre-strained and repetitive-strained CrMoV rotor-steel specimens. It was found that the creep-crack growth rates, da/dt, of the creep-pre-damaged specimens were larger than those of virgin specimens under constant load. It was also found that under the same stress intensity factor K, da/dt in the case of about 10%-crept and creep void induced specimens was increased five times, while in the case of 0.8%- and 2.8%-crept specimens, it only increased a little. However, all the data fell in a narrow scatter band in the relationship between C* and da/dt. The effect of long-term operating degradation appeared on the creep- and fatigue-damage under the Slow-Fast waveform. Also the crack density was larger in the damaged specimens compared with the virgin specimens. Other results showed that the fatigue-crack growth rates, da/dN, of creep- and fatigue-pre-damaged specimens were larger than those of virgin specimens. Under the same stress intensity factor range ΔK, da/dN in a specimen with approximately 10%-creep was increased 20 times. Moreover da/dN in fatigue-pre-damaged specimens was accelerated 10 times. However, the results of the strain-controlled crack growth test fell in a narrow scatter band in the relationship between J integral range ΔJ and da/dN. These results suggest that the creep remaining lives and fatigue remaining lives of mechanically damaged CrMoV steel can be estimated using the C* & ΔJ values considering the creep rate and the deformation rate of the pre-damaged materials and the da/dt and da/dN values of the virgin material.

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Comparison Between Crack Growth in Fracture Mechanics Specimens and Feature Component Tests Carried Out in a Low-Alloy Steel

Journal of Pressure Vessel Technology ◽

10.1115/1.556147 ◽

1999 ◽

Vol 122 (1) ◽

pp. 40-44 ◽

Cited By ~ 1

Author(s):

Kamran Nikbin

Keyword(s):

Fracture Mechanics ◽

Crack Growth ◽

Creep Crack Growth ◽

Compact Tension ◽

Growth Data ◽

Good Correspondence ◽

Creep Crack ◽

Growth Properties ◽

Circumferential Defects ◽

Testing Condition

In both power generation plants and the chemical industries, there is a need to assess the significance of defects which may exist in high-temperature equipment operating in the creep range. This paper examines the methods of analysis used in laboratory creep crack growth data and their relevance to crack growth data derived from feature component tests which best simulate actual components under controlled testing condition. The material examined was a 214 Cr 1 Mo steel in the new condition at 550 and 600°C. The creep crack growth properties were determined on compact tension specimens. The data were compared with representative crack growth data from feature test components. These consisted of cracked rings, thick-walled cylinders, and thin-walled tubes containing axial or circumferential defects under combinations of axial and internal pressure loading. Little influence of size or temperature on the measured crack propagation rates was observed when the results were plotted against the creep fracture mechanics parameter C*. This is shown to be because the relevant condition had little effect on the appropriate crack tip creep ductilities of the material. Good correspondence was observed between the compact tension and the feature component tests, suggesting the feasibility of the C* method for predicting short-term laboratory tests using different geometries. [S0094-9930(00)01001-5]

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