Fatigue Crack Growth Property for

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10th International Conference Pressure Vessel
Technology Vienna, July 8, 2003
Fatigue Crack Growth Property for Application of
Fatigue Design
Katsumasa Miyazaki Mechanical Engineering
Research Laboratory, HITACHI, Ltd. Ibaraki, Japan
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Background
- ASME Boiler Pressure Vessel Code Sec.VIII,
Div. 3
ARTICLE KD-4 FRACTURE MECHANICS EVALUATION
If a leak-before-break mode of failure cannot be
shown, then the number of design cycles shall be
calculated in accordance with this Article
Fatigue Crack Growth Evaluation
- Design Process In-service Inspection
Program (ISI Period, NDE Method etc...)
Crack Growth Behavior
Crack Growth Evaluation
For the Crack Growth Evaluation based on the
Fracture Mechanics Concept
- Stress Intensity Factor Confirmation by
Analysis - Fatigue Crack Growth Property Need
the Experiments
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Procedure of Fatigue Crack Growth Evaluation
Fatigue Crack Growth Property
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Crack Growth Behavior
By using fracture mechanics concept, the cycles
for stable crack growth region can be estimated.
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Problems about Estimation of Fatigue Crack
Growth Property
The crack growth rate in elevated temperature
water (LWR conditions) is higher than that in air.
Environmental Assisted Cracking (EAC)
Proposal of Fatigue Crack Growth Property
- Effect of Environmentally Assisted Factors -
Material Factor (Sulfur Content in Material) -
Loading Factor (Stress Ratio and Rise Time,
etc.) - Environment Factor (Dissolved Oxygen
etc.)
- Effect of the Difference between Deepest and
Surface Points of Surface Crack
Schematic of Surface Crack
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Example of Proposal of Fatigue Crack Growth
Property for Carbon Steel in BWR Environment
Material Carbon Steel Pipe for High Pressure
Service, JIS STS410 (JIS Japanese Industrial
Standard)
Simulated BWR Environment Temperature 288deg.C
Pressure 8 MPa Dissolved Oxygen 0.2ppm Con
ductivity lt 0.1mS/cm
100
25
180
400
80
Schematic of Flat Plate Specimen (Loading
Pattern Tension)
National Project , Structural Assessment of
Flawed Equipment (SAF) 1991 - 2000
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Modeling of the Crack Growth Property in BWR
Environment
Upper Slope Curve
Second Slope Curve
in Air
Crack Growth Rate, da/dN
On Time domain Form
Threshold Curve
for Threshold Curve
DK1
DK2
DK0
Stress Intensity Factor, DK
Relationship between da/dN and DK
Relationship between DKth and R
The crack growth property for carbon steel in BWR
environment is modeled using upper slope, second
slope and threshold curves.
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Upper and Second Slope Curves on Time Domain
Form for Surface Crack (at Deepest Point)
(a) at Deepest Point for Surface Crack
The upper and second slopes at the deepest point
can be determined as envelope curves on time
domain form of carbon steel.
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Proposed Fatigue Crack Growth Property for Carbon
Steel in BWR Environment
Threshold Curve
DK0 9.20 - 3.09R
DK1 Value
DK2 Value
Second Slope Curve
CT Specimen da/dN 162.12?C(DK)n Deepest
Point da/dN 61.71?C(DK)n Surface Point
da/dN 229.67?C(DK)n
Relationship between da/dN and DK
Upper Slope Curve
CT Specimen da/dN 0.0130 ? TR0.536? C0.464
(DK) 0.464n Deepest Point da/dN 0.0211 ?
TR0.475? C0.525 (DK) 0.525n Surface Point
da/dN 0.0052 ? TR0.648? C0.352 (DK) 0.352n
C 3.57 x 10-9 x S, S (10.30R)?(E0/E)0.51n,
n 3.02
Proposed curve is function of rise time and
stress ratio.
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Comparison Experimental Data with Proposed Crack
Growth Property
Surface Crack
Surface Crack
Deepest Point
Surface Point
Stress Intensity Factor Range, DKB (MPa (m)0.5)
Stress Intensity Factor Range, DKA (MPa(m)0.5)
(a) at Deepest Point
(b) at Surface Point
Rise time 2500 s
Proposed curve can estimate the experimental data
with appropriate margin.
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Conclusion
- Fracture Mechanics Concept
Fatigue Design (Design Procedure)
- Estimation of fatigue crack growth property for
each material in actual environment will be key
technology.
Environmental Assisted Cracking
- Material Factor - Loading Factor - Environment
Factor
- For the proposal of the appropriate fatigue
crack growth property, the systematic experiments
with considering the EAC effect will be needed.
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Conclusion (Contd)
- For the application of fracture mechanics
concept to design, the limitation of fracture
mechanics evaluation should be considered.
(Fatigue Life of Actual Component) (Cycles to
Initiation of Crack) (Cycles to Propagation
of Crack)
Fracture mechanics can be applied for the
estimation of cycles to propagation of crack,
only.