Nano-scale Residual Stress Evaluation
Transcript of Nano-scale Residual Stress Evaluation
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Residual Stress Evaluation Instrumented Indentation Testing
2018. 03. 26.Jun Sang Lee
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1. Residual Stress Evaluation Using Instrumented Indentation Test
2. Stress-Free State Estimation
3. Evaluation of Residual Stress and Failure Sensitivity of Drive Shaft
4. LTT Welding Integrity Evaluation
Contents
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Instrumented Indentation Test
A novel method to characterize mechanical properties
HardnessElastic modulusTensile propertiesResidual stressFracture toughness
Indentation load-depth curve
Load
Depth
Loading
Unloading
“fingerprint of material”
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0S LLL −=∆
) L( S =
ht
ΔL
ΔL
LT
L0
Depth
LoadCompressive Tensile
Stressfree
LCTensile stress
Compressive stress
Indentation Load-Depth Curves
CLTL or
Vickersindenter
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Basic Principle
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Non-equibiaxial residual stress
xres
yresp
σσ
=
σ+
σ+
σ+
xres
xres
xres
)p(
)p(
)p(
3100
03
10
003
1
σ+
−
σ−
σ−
xres
xres
xres
)p(
)p(
)p(
3100
03
120
003
2
σσ
0000000
yres
xres
σσ
0000000
xres
xres
p
hydrostatic stress deviatoric stress
xresσ
yresσ
x
y
z
Stress Ratio :
Stress Tensor
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xresσ
3p)(1+
S
xres A
L1p)(1
3σ ∆Ψ+
=
S
xres A
L1σ3
p)(1 ∆Ψ
=+
=
σσ
= AreaContact,p xres
yres A S
Deviatoric stress along Z direction : Indentation stress :
intσ
Ψ
=SA
ΔL1
where , = constraint factor (3.0)Ψ
L σxres ∆∝
Residual Stress Indentation Load
Residual Stress Evaluation by IIT
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Code Case N-881<Code Case N-881>
Exempting SA-508 Grade 1A from PWHT Based on Measurement of Residual Stress in Class 1 Applications
• Work period : 2013.03 ~ 2017.12
• Session : Section III
Construction of Nuclear Facility Component
• ASME Code Case N-881 – Approved in 2017
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1. Residual Stress Evaluation Using Instrumented Indentation Test
2. Stress-Free State Estimation
3. Evaluation of Residual Stress and Failure Sensitivity of Drive Shaft
4. LTT Welding Integrity Evaluation
Contents
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4 8 12 16 20 24
1.02
1.05
1.08
1.11
1.14
1.17
1.20
f = h
c/hm
ax
hm/(hm-hf)
Carbon steel (9) Stainless steel (7) Al alloy (2) Ti alloy (3) Ni alloy (1) Cu alloy (2) Mg alloy (3)
00.11090.9max
max3
max
+−
×== −
f
c
hhh
hhf
For 27 metallic materials- S.K. Kang et al., J. Mater. Res. (2010)
Contact area equation for sharp indenter
9/41
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f-function Model
𝐻𝐻𝑣𝑣,0𝑡𝑡 = 𝐻𝐻𝑣𝑣,𝑠𝑠
𝑡𝑡 [Swadener, Pharr, 2001]
• 𝐴𝐴𝑐𝑐 , ℎ𝑐𝑐 are invariant to residual stress.
• ℎ𝑚𝑚𝑚𝑚𝑚𝑚 − ℎ𝑓𝑓 is invariant to residual stress.
• ℎ𝑚𝑚𝑚𝑚𝑚𝑚,𝑡𝑡0 is obtained using f-function.
hmax0 kℎ𝑐𝑐𝐴𝐴𝑐𝑐
𝐴𝐴𝑐𝑐 = 24.5ℎ𝑐𝑐2𝑓𝑓 − 𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓
(ℎ𝑐𝑐 & ℎ𝑚𝑚𝑚𝑚𝑚𝑚 − ℎ𝑓𝑓 𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓)𝐾𝐾𝑓𝑓𝑓𝑓𝑘𝑘′𝑠𝑠 𝑟𝑟𝑟𝑟𝑙𝑙
S-F curve
1.00hh
h100.99hh
fmax
max2
max
c +−
×= −
𝐿𝐿 = 𝑘𝑘ℎ2
L
h
Stress-free
Tensile
Compression
Assumption
Equation
[T.Y. Tsui et al., J. Mater, Res (1996)][A. Bolshakov et al., J. Mater, Res (1996)]
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Verification Test
Indentation on bending state
Elastic stress field by bending
-300 -200 -100 0 100 200 300-300
-200
-100
0
100
200
300
Anal
yzed
stre
ss b
y In
dent
atio
n (M
Pa)
Applied stress by bending (MPa)
- Material : SA-508 Grade 1A
- Test Equipment : Indentation AIS 3000, FRONTICS
- Test Condition : 50 kgf load condition
Applied Stress Specimen
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Invariant Parameter Analysis in Nano Scale
#1 #2 #3 #4 #5 #60
50
100
150
200
250
300
350
400
hmax
-hf
Position#1 #2 #3 #4 #5 #6
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
m
Position#1 #2 #3 #4 #5 #6
0.0
0.2
0.4
0.6
0.8
1.0
Stiff
ness
Position
Position 1 2 3 4 5 6
Stress(Mpa) -135.602 -61.4133 12.775 86.96333 161.1517 235.34
Target Material : SUS316(Bulk)
Specimen Treatment : Heat treatment for stress relaxation
Maximum Load : 60mN
Test Condition
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Comparing Invariant Parameters ( Bulk vs Thin film)
1.0
1.5
2.0 m
15
20
25
30 hmax-hf
0.10
0.15
hc
0.12
0.14
Stiffness
Black– bulk (4point bending)Red – thin film
Invariant parameters of thin film have greater deviation than bulk metal(∵inhomogeneous deposition & roughness effect)
⇒ hmax-hf, hc have less deviation than m.
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Contact Area Mesurement
𝒂𝒂 𝒃𝒃𝒄𝒄
𝑺𝑺 = 𝒔𝒔(𝒔𝒔 − 𝒂𝒂)(𝒔𝒔 − 𝒃𝒃)(𝒔𝒔 − 𝒄𝒄) ( 𝒔𝒔 = 𝒂𝒂+𝒃𝒃+𝒄𝒄𝟐𝟐
)
• AFM resolution limit degrades accuracy of indentation area
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Substrate Effect
3t
2t
t
- Thin film with various deposition depth
- Check the change of curve depending on ℎ𝑚𝑚𝑚𝑚𝑚𝑚𝒕𝒕
with same load condition
Different material
𝒉𝒉𝒄𝒄( 𝑨𝑨𝒄𝒄), 𝒉𝒉𝒎𝒎𝒂𝒂𝒎𝒎 − 𝒉𝒉𝒇𝒇 𝒉𝒉𝒎𝒎𝒂𝒂𝒎𝒎
𝒉𝒉𝒄𝒄( 𝑨𝑨𝒄𝒄), 𝒉𝒉𝒎𝒎𝒂𝒂𝒎𝒎 − 𝒉𝒉𝒇𝒇 𝒉𝒉𝒎𝒎𝒂𝒂𝒎𝒎
Estimation
hmax/t = 3/10 hmax/t = 2/10
Load
depth h𝐿𝐿0.0
0.1
0.2
0.3
0.4
0.5
hmax/t
𝒉𝒉𝑳𝑳𝒕𝒕
Plastic zone
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1. Residual Stress Evaluation Using Instrumented Indentation Test
2. Stress-Free State Estimation
3. Evaluation of Residual Stress and Failure Sensitivity of Drive Shaft
4. LTT Welding Integrity Evaluation
Contents
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1
2
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Fracture Analysis
Fatigue striation
Qusai-cleavage
Dimple rupture
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Fatigue striation
Fatigue striation
Dimple rupture
Dimple rupture
3Dimple rupture
Corrosion particle
cleavage
4cleavage
1
2
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2
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Issue 1 Resolution: Evaluation for inner slope part
- Insturmented Indentatiton test on the slope of the inner part of drive shafts
- The inner shape of the drive shaft is different for each part
ㆍ 6 axis jig
ㆍ Results
→ Manufacture jig for Micro-AIS with adjustable angle
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Issue 2 Resolution : Optimal test angle
- For correct data indentation direction should be perpendicular to the surface of specimen.
- Symmetrical curve were generated according to the test angle change with reference curve
(perpendicular direction)
ㆍ Optimal test angle setting
ㆍ Results
0.0 0.5 1.0 1.5 2.0 2.5 3.0
0
20
40
60
80
0˚ 3˚ 7˚
0 (0
)
Depth(um)
0.0 0.5 1.0 1.5 2.0 2.5 3.0
0
20
40
60
80
0˚ -3˚ -7˚
Load
(g)
Depth(um)
• Maximum indentation depth increases with test angle
→ Determine the optimal test angle condition for each specimen
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Residual Stress Results
Over Normal 하0
50
100
150
200
250
300
RS (M
pa)
Heat treatment condition
ㆍ Evaluation Results SampleRS (MPa)Heat
treatment#
Over heat
1 305.98
2 234.09
3 238.66
4 186.67
Ave 241.35
Normal heat
1 126.42
2 122.82
3 136,65
4 112.80
Ave 124.67
Under heat
1 80.61
2 104.41
3 102.11
4 97.68
Ave 96.20
※ Tensile Stress- Over heat : 70% of YS- Normal heat : 36% of YS- Under heat : 28% of YS
(YS : over 343 MPa )
Tensile residual stress increases as out surface heat
treatment condition.(→ For accurate analysis, applied stress information during operation should
be added)
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m.
r F)/a(RSK 501000πΙ =
))t/a(..)t/a(..)(t/a(.Fm πθπθ 94414855077216152410101 −++=
IC
IrKK
Af ⋅= 22
RS : residual stressa : Depth of crack (assume as 2mm)
Evaluation of Failure Sensitivity of Drive Shaft
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1. Residual Stress Evaluation Using Instrumented Indentation Test
2. Stress-Free State Estimation
3. Evaluation of Residual Stress and Failure Sensitivity of Drive Shaft
4. LTT Welding Integrity Evaluation
Contents
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LTT(Low Transformation Temperature) Welding
Basic Principle
Strain by Phase Transformation Compressive Residual stress/strain
The novel welding method with relatively low temperature martensitic transformation of welding filler
Definition
Reducing tensile residual stress or inducing compressive residual stress in weld material
Purpose
(Application of low Ms temperature consumable to dissimilar welded joint, 2014)
(a) Conventional welding
(b) LTT welding
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[C/S welding] [LTT welding]
C/S welding & LTT welding
C/S (Carbon steel) welding & LTT welding
Angular Distortion
Vickers Hardness
YS, UTS
CVN test
Residual Stress
Validation of LTT welding by comparing convational welding
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Weld material Type Welding
1 TGC-50 (C/S)Bead on plate TIGW
-
2 GSCO12 (Ni- LTT) -
3 K-71T (C/S)
Butt Joint FCAW
-
4 K-71T (C/S) PWHT
5 MX-4AD (Mn- LTT) -
6 MX-4AD & K-71T Partial
C/S (Carbon steel) welding & LTT welding(Base Metal : A516 70N)
C/S welding & LTT welding
Partial LTT Welding
* Welding Process and Consumables Aimed at Improving Fatigue Strength of Joints, Minoru MIYATA, 2016 (KOBELCO)
Cross-sectional shape of additional weld
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Summary
Welding Method C/S Ni- LTT Mn- LTT Partial LTT
Angular distortion (°) 3.43 2.64 - -
Residual stress (MPa) 150.8 -323.2 -381.2 -333.8
Vickers Hardness (HV) 227.5 386.9 228.4 287.3
Absorbed energy (J) 255.3 45.0 53.3 146.9
Yield strength (MPa) 356.7 919.6 673.5
Tensile strength (MPa) 741.6 1106.0 743.3
Weld region results
Welding Integrity
Mechanical Properties
• LTT welding has excellent welding integrity.(WRS reduction : Mn-LTT > Partial LTT > Ni-LTT)
• Relatively poor mechanical properties (Hardness & Absorbed E)
compared with conventional welding
• Partial LTT welding shows excellent properties and integrity both.
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Measure strain rate during welding using strain gauge
Start
Center
End
0 1 2 3 4 5
-3000
-2000
-1000
0
1000
2000
3000
C/S welding LTT welding
ε (St
rain
)
# of Pass
Start
0 1 2 3 4 5-3000
-2000
-1000
0
1000
2000
3000
C/S welding LTT welding
ε (St
rain
)
# of Pass
Center
0 1 2 3 4 5
-3000
-2000
-1000
0
1000
2000
3000
C/S weldingLTT welding
ε (St
rain
)
# of Pass
End
Measure Welding Strain
Measure residual stress due to martensic transformation by comparing with conventional welding
[Using strain gauge]
Construction of Strain D/B for Welding Processes
[5 Pass welding]
Strain
Purpose : Investigate the effect of phase transformation of martensite to residual stress
Thermal Expansion
Martensic TransformationStress
High tep. Tesnsile test(E, Thermal Coefficient, YS, TS..)
Stress by phase transformationExpect thermal stress