Residual Stress Evaluation Instrumented Indentation Testing 2018. 03. 26. Jun Sang Lee

1

Residual Stress Evaluation Instrumented Indentation Testing

2018. 03. 26.

Jun Sang Lee

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

Hardness

Elastic modulus Tensile properties Residual stress Fracture toughness

Indentation load-depth curve

Load

Depth

Unloading

“fingerprint of material”

3

0

S L

L L = −

∆

h_t

ΔL

ΔL L

L

Depth Lo ad

Compressive Tensile Stress

free

L

Tensile stress

Compressive stress

Indentation Load-Depth Curves

Vickers indenter

136

Basic Principle

5

Non-equibiaxial residual stress

x res y

p

σ

= σ





















+ σ + σ

+ σ

x res x

res x

res

) p ( )

p ( )

p (

3 0 1

0

3 0 0 1

0 3 0

1





















+ σ

−

− σ

− σ

x res x

res x

res

) p ( )

p ( )

p (

3 0 1

0

3 0 1 0 2

0 3 0

2

















σ σ

0 0

0

0 0

0 0

y res x

res

















σ σ

0 0

0

0 0

0 0

x res x

res

p

hydrostatic stress deviatoric stress

x

σ

y

σ

y

z

Stress Ratio :

Stress Tensor

x

σ

3 p) (1 +

S x

res

A

L 1

p) (1

σ 3 ∆

Ψ

= +

S x

res

A

L σ 1

3 p)

(1 ∆

= Ψ +

 

 



 =

σ

= σ , Contact Area

p

res y

res

A

Deviatoric stress along Z direction : Indentation stress :

σ

_



 





= Ψ

A

ΔL 1

where , = constraint factor (3.0)Ψ

L σ

∝ ∆

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

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

/h

h

/(h

-h

)

Carbon steel (9) Stainless steel (7) Al alloy (2)

Ti alloy (3) Ni alloy (1) Cu alloy (2) Mg alloy (3)

00 . 1 10

90 . 9

max 3 max max

− +

×

=

=

f c

h h

h h

f h

For 27 metallic materials

Contact area equation for sharp indenter

9/41

f-function Model

𝐻𝐻

= 𝐻𝐻

• 𝐴𝐴_𝑐𝑐, ℎ_𝑐𝑐 are invariant to residual stress.

• ℎ_{𝑚𝑚𝑚𝑚𝑚𝑚} − ℎ_𝑓𝑓 is invariant to residual stress.

•ℎ_{𝑚𝑚𝑚𝑚𝑚𝑚,𝑡𝑡}⁰ is obtained using f-function.

h

k

ℎ

𝐴𝐴

𝐴𝐴𝑐𝑐 = 24.5ℎ𝑐𝑐2 𝑓𝑓 − 𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓

(ℎ𝑐𝑐& ℎ𝑚𝑚𝑚𝑚𝑚𝑚− ℎ𝑓𝑓𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓) 𝐾𝐾𝑓𝑓𝑓𝑓𝑘𝑘^′𝑠𝑠 𝑟𝑟𝑟𝑟𝑙𝑙

S-F curve

h 1.00 h h 10 hh 0.99

f max 2 max 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

Analyzed stress by Indentation (MPa)

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

Invariant Parameter Analysis in Nano Scale

#1 #2 #3 #4 #5 #6

0 50 100 150 200 250 300 350 400

hmax-hf

#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

#1 #2 #3 #4 #5 #6

0.0 0.2 0.4 0.6 0.8 1.0

Stiffness

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.

Contact Area Mesurement

𝒂𝒂 𝒃𝒃 𝒄𝒄

𝑺𝑺 = 𝒔𝒔(𝒔𝒔 − 𝒂𝒂)(𝒔𝒔 − 𝒃𝒃)(𝒔𝒔 − 𝒄𝒄) ( 𝒔𝒔 = ^{𝒂𝒂+𝒃𝒃+𝒄𝒄}_𝟐𝟐 )

15

Substrate Effect

3t 2t t

- Thin film with various deposition depth

- Check the change of curve depending on ^{ℎ𝑚𝑚𝑚𝑚𝑚𝑚}

𝒕𝒕 with same load condition

Different material

𝒉𝒉_𝒄𝒄(𝑨𝑨_𝒄𝒄), 𝒉𝒉_{𝒎𝒎𝒂𝒂𝒎𝒎}−𝒉𝒉_𝒇𝒇 𝒉𝒉_{𝒎𝒎𝒂𝒂𝒎𝒎}

𝒉𝒉_𝒄𝒄(𝑨𝑨_𝒄𝒄), 𝒉𝒉_{𝒎𝒎𝒂𝒂𝒎𝒎}−𝒉𝒉_𝒇𝒇 𝒉𝒉_{𝒎𝒎𝒂𝒂𝒎𝒎}

Estimation

hmax/t = 3/10 hmax/t = 2/10

Load

depth h_𝐿𝐿

0.0 0.1 0.2 0.3 0.4 0.5

hmax/t 𝒉𝒉𝑳𝑳

𝒕𝒕

Plastic zone

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

3 4

1

2

3

4

Fracture Analysis

Fatigue striation Qusai- cleavage

Dimple rupture

1

Fatigue striation Fatigue striation

Dimple rupture

Dimple rupture

3

Dimple rupture

Corrosion particle cleavage

4

cleavage

1

2

3

4

2

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

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

3˚0˚

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

Residual Stress Results

Over Normal 하

0 50 100 150 200 250 300

RS (Mpa)

Heat treatment condition

ㆍ Evaluation Results

RS (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

1 80.61

2 104.41

※ 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

21

m .

r

RS ( a / ) F

K

= π 1000

)) t / a ( .

. ) t / a ( .

. )(

t / a ( .

F _m = 1 10 + 0 15241 + 16 772 θ π 0 855 − 14 944 θ π

IC Ir

K A K

f ₂ = ₂ ⋅

RS : residual stress

a : Depth of crack (assume as 2mm)

Evaluation of Failure Sensitivity of Drive Shaft

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

[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

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

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



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)

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 (Strain)

# of Pass Start

0 1 2 3 4 5

-3000 -2000 -1000 0 1000 2000

3000 C/S welding

LTT welding

ε (Strain)

# of Pass Center

0 1 2 3 4 5

-3000 -2000 -1000 0 1000 2000

3000 C/S welding

LTT welding

ε (Strain)

# 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 Transformation

Stress

High tep. Tesnsile test (E, Thermal Coefficient, YS, TS..)

Stress by phase transformation Expect thermal stress