Understanding of the limiting condition for ductile components
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ndrew Wasylyk UNTF 2011 Understanding of the limiting condition for ductile components Andrew Wasylyk UNTF 2011
description
Understanding of the limiting condition for ductile components. Andrew Wasylyk. UNTF 2011. plastic zone . Plastic zone. Fracture process area. Defining Limiting Condition. Ductile components. Primary pipe work is fabricated from Grade 304 stainless steel Typical yield stress 250MPa - PowerPoint PPT Presentation
Transcript of Understanding of the limiting condition for ductile components
Andrew Wasylyk UNTF 2011
Understanding of the limiting condition for ductile components
Andrew Wasylyk
UNTF 2011
plastic zone
Fracture process areaPlastic zone
Defining Limiting Condition
Ductile components
• Primary pipe work is fabricated from Grade 304 stainless steel
• Typical yield stress250MPa
• Typical ductility60 - 70%
Aim
Define cases under which structural integrity of ductile components may be solely assessed on plastic collapse
criteria, whilst maintaining the integrity of the plant
Fracture above limit load
From SPECIMEN to STRUCTURE
Size effect!
Defining Fracture
• J-integral– Conventional methodology to
define critical crack tip stress field– Validity limits– Dependence on global plasticity
0 2 4 6 8 10 120.0
0.5
1.0
1.5
LEFM+EPFM Defined Fracture
fracture can be defined by :K, J,J-T,J-Q
L r cra
ck le
ngth
cor
rect
edLLD (mm)
ASME TES
How do we define fracture?
Limit Load
Ductile Fracture
• Local Approach– Rice & Tracey local approach– Defined for ductile behaviour, growth of a void to
a critical void volume fraction.– Proportional to stress, strain and triaxiality ahead
of the crack tip– Will account for constraint effects.
Fracture Toughness Specimens:
• a/W=0.55
• Unloading compliance methodology• Crack propagation proportional to elastic unload• Global J proportional to area under the load
displacement curve• Tracking of plasticity development using Digital Image
Correlation
Experiments
Aim Analyse fracture under a range of Plasticity conditions Compare methodologies defining fracture under large plasticity conditions
Experimental results
0.0 0.5 1.0 1.5 2.0 2.50
1000
2000 25mmCT ASTM 1820 Validity limit 15mmCT ASTM 1820 Validity limit 10mmCT ASTM 1820 Validity limit
J0.2BL=160 MPa mm
J0.2BL=300 MPa mm
B=10 mm
J
(MPa
mm
)
a (mm)
B = 25mm
B=15 mm
J0.2BL
=700 MPa mm
25mmCT
15mmCT
10mmCT
0.0 0.5 1.0 1.5 2.00
50
100
150
200
250
300
350
400
450
500
J
(MPa
mm
)
a (mm)
4-10a
c
b
e
d
f hg
k
a
c
b
g
f
h
d
e
25mmCT 15mmCT
10mmCT
Finite Element Analysis• Boundary Layer analysis • 3D Compact Tension
Local Approach
Rice and Tracey Ductile criterion
pmm d
RR f
0
0 23cosh**008.0
23sinh*558.0ln
Void growth in triaxial stress fieldGeneralised form based on a
range of shape factors
Local Approach
B = 10 mm B = 15 mm B = 25 mm
J (MPa mm)0 200 400 600 800
0.00
0.02
0.04
Gen
eral
Ric
e &
Tra
cey
(per
uni
t vol
ume)
Conclusion
Fracture behaviour of small scale specimens can be defined using a modified Rice and Tracey
approach
Small scale specimen can be used to define fracture behaviour without over-conservatism
Plasticity is self similar in all specimens
THANK YOU FOR YOUR ATTENTION!Any Questions?
Image Correlation
• Optical tracking of local displacement of features on the surface of the specimen
• Surface preparation:– 25mm CT: White paint coating with
random black speckles– 15mmCT & 10mmCT: Oxalic Acid
electro-etching, I=6V,t=12min
0 2 4 6 8 10 120.0
0.5
1.0
1.5
LEFM+EPFM Defined Fracture
fracture can be defined by :K, J,J-T,J-Q
L r cra
ck le
ngth
cor
rect
ed
LLD (mm)
ASME TES
How do we define fracture?
Limit Load
Fracture above limit load
Region I: LEFM
Region II: EPFM
Region III: J-QLocal ApproachEnergy Dissipation
