1

Residual Stress Evaluation Instrumented Indentation Testing

2018. 03. 26.Jun Sang Lee

2

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

3

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”

3

4

0S LLL −=∆

) L( S =

ht

ΔL

ΔL

LT

L0

Depth

LoadCompressive Tensile

Stressfree

LCTensile stress

Compressive stress

Indentation Load-Depth Curves

CLTL or

Vickersindenter

136

Basic Principle

5

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

6

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

7

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

7

8

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

9

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

10

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)]

11

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

12

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

13

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.

14

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

15

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

16

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

17

1

2

34

1

2

34

Fracture Analysis

Fatigue striation

Qusai-cleavage

Dimple rupture

1

Fatigue striation

Fatigue striation

Dimple rupture

Dimple rupture

3Dimple rupture

Corrosion particle

cleavage

4cleavage

1

2

34

2

18

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

19

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

20

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)

21

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

22

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

23

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

24

[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

25

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

26

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.

27

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