fatigue strenght of welded joints

1

11

Retrofit Engineering for Urban Infrastructures, Lecture #3

Chitoshi Miki

Fatigue Strengthof Welded Joints

Department of Civil EngineeringTokyo Institute of Technology

22

ContentsEffects of Residual Welding Stresseson Fatigue Crack Growth Rate

Size EffectsFull Size Fatigue Tests of Truss Chords

Fatigue Strength of Large-Size Gusset Jointsof 800MPa Class Steels

High Strength Steels

Longitudinal Welded Joints Containing Blowholes

Butt-Welded Joints Containing Various Embedded Defects

Effects of Weld Defects on Fatigue Strengths

33

Effects of Residual Welding Stresseson Fatigue Crack Growth Rate

Topic 1

44

Fatigue Crack Propagation Rate, da/dN

Fatigue LifeCrack Initiation Life, Ni

Crack Propagation Life, Np

Evaluation of Np

ΔK－da/dN Relationship

Affected by Residual Welding Stresses?

Experimental Investigations

55

Specimen ASpecimen B : One Longitudinal WeldingSpecimen C : Two Longitudinal Welding

I: A Crack on Base Metal

II: A Crack on Weld Metal

Specimens

800Mpa Class Steels

66

Measurements of Residual Stress

Location of Strain Gauges

2

77

Change of Residual StressDue to Crack Propagation

Half Length of Fatigue Crack (mm)

Stre

ss

(MPa

)

88

Change of Residual Stress DistributionDue to Crack Propagation

L

B-I Type Specimen

Wel

ding

L=60 mm

Stre

ss

L=0 mm

99

Change of Residual Stress DistributionDue to Crack Propagation

C-I Type Specimen

L

Wel

ding

Wel

dingSt

ress

Wide Tensile Region

1010

ΔK－da/dN Relationship (1)

L

A-I Type SpecimenNo Weld-Beads

ΔK

da/d

N

( ) 675.25.113 1071.2]/[1054.6]/[ −− ×−∆×= mmNKcyclemmdNda

Equation 1

1111

ΔK－da/dN Relationship (2)

da/d

N

ΔK


A-I

OthersNo Significant Differences Between The Other Typesof Specimens

Equation 2

1212

Estimation of Fatigue Crack Propagation Life, Np



Penny-ShapedFatigue Crack

(Radius:a)

Welded Joint Model

Equation 2

Equation 1

3

1313

Estimation of Fatigue Crack Propagation Life, Np

Equation 1, ai=0.1

Equation 1, ai=1.0 Equation 2, ai=0.1

Equation 2, ai=1.0

Np

Δσ

1414

Effects of Weld Defects on Fatigue StrengthsLongitudinal Welded Joints

Containing Blowholes

Topic 2

1515

Welded Joint Specimen

Small Specimen

Specimens 1616

Residual Stress Distributionin The Welded Joint Specimen

1717

Classification of Blowhole Sizes

No Blowholes

Small Blowholes b < 1mm

1 mm < b < 2mmMedium Blowholes

b: Blowhole Length

Large Blowholes b > 2mm

Base on Radiographic Examination

1818

Large Blowholes

Small Blowholes

Category A

Category B

Fatigue Test Results

4

1919

Fatigue Cracks Originated From Blowholes

Radiograph Radiograph

Crack Crack Crack

2020

Fracture Surfaces with Beach Marks

2121

Fatigue CrackPropagationfrom Blowholes

2222

Fatigue CrackPropagation Ratefrom Blowholes

( ) 0.3131097.2 KdNda

∆×= −

( ) 0.3131090.0 KdNda

∆×= −

( ) 80.313 1034.81073.1 −− ×−∆×= KdNda

2323

Topic 2

Effects of Weld Defects on Fatigue StrengthsButt-Welded Joints

Containing Various Embedded Defects

2424

•Butt welded joint with V-groove

Incomplete Penetration (IP)

Lack of Fusion (LOF)

Blowhole(BH)

Slag Inclusion(SI)

Crack(CR)

Various Embedded Weld Defects

5

2525

Specimen PreparationSpecimen PreparationCutting lines

Z

X

Y

Weld defects

Specimen

Specimen

Specimen

JIS SM490A: 150 specimensJIS SM570Q: 27 specimens

JIS SM570Q567567497497DWDW--Z100Z100532532343343SM490SM490

TS(MPaTS(MPa))YP(MPaYP(MPa))

614614534534DWDW--6060660660588588SM570SM570--QQ

TS(MPaTS(MPa))YP(MPaYP(MPa))

JIS SM490A

← Detected by RT

2626

Specimen ConfigurationSpecimen Configuration

25

As-welded condition

0

500

7Root gap

R100

100 300

0

170100

4

30°

99 0

Weld bead

Uniformed section

30 °

Weld detail,V-groove

25

7

2727

Fatigue TestFatigue Test

Testing machineTesting machine–– Capacity: 300 kNCapacity: 300 kN

Testing conditionsTesting conditions–– Constant amplitudeConstant amplitude–– Stress ratio R=0Stress ratio R=0–– Maximum stress:Maximum stress:

100 100 -- 350 MPa350 MPa

Specimen

2828

Fatigue Test ResultsEvaluation : defect length “2c” is used.

Single defect Multi defects

RS(Real size

measured on failure

surface)

Length 2cX

Z

2c1 2c2

RT(Xray)

WES 2805Real Size

S

S0 = 0.25 x min (c1,c2)S ≤ S0 → 2c = 2c1 + 2c2+S S > S0 → cracks are isolated

Depth 2a

2929

Fatigue Test Result, CR Type DefectFatigue Test Result, CR Type Defect(SM490A)(SM490A)

104 105 106 10760708090

100

200

300

400

Fatigue Life (cycles)

Stre

ss R

ange

(MPa

)

209

9

67

911

132328

26

40

40

15

15

15

10

210

24

29

53

CJSSC-class => D

2

B A

RTRTToeToe

RSRSDefectDefect

lengthlengthinitiationinitiation

3030

Fatigue Test Result, IP Type DefectFatigue Test Result, IP Type Defect(SM490A)(SM490A)

104 105 106 10760708090

100

200

300

400


Stre

ss R

ange

(MPa

)

611

8.513

22

34.5

34.5 2440

30

30

30

297 15

40

2

40

2

2

2 8

21

21.5

CJSSC-class =>D

1026 2025

AB

RTRTToeToe

RSRSDefectDefect


6

3131

Fatigue Test Result, LOF Type DefectFatigue Test Result, LOF Type Defect(SM490A)(SM490A)

104 105 106 10760708090

100

200

300

400


Stre

ss R

ange

(MPa

)

109

6

9.5 4 4

12

127.5

8

9 6.5

11.3

8.52

11.3

6.53

4.510.5

CJSSC-class =>D AB

RTRTToeToe

RSRSDefectDefect


3232

Fatigue Test Result, SI Type DefectFatigue Test Result, SI Type Defect(SM490A)(SM490A)

104 105 106 10760708090

100

200

300

400


Stre

ss R

ange

(MPa

)

8.55

15

1521

2324.5 16.2

7

3219

19

21

21

2121

13 18

21

216

121325

CJSSC-class => D

19

19

8

B A

RTRTToeToe

RSRSDefectDefect


3333

Fatigue Test Result, BH Type Fatigue Test Result, BH Type Defect(SM490A)Defect(SM490A)

104 105 106 10760708090

100

200

300

400


Stre

ss R

ange

(MPa

)

10 55

14

14

2

2

162 4

4

3

12511

2

2 311

CJSSC-class => D B A

RTRTToeToe

RSRSDefectDefect


3434

High Strength SteelsFatigue Strength of Large-Size Gusset Joints

of 800MPa Class Steels

Topic 3

3535

Types of Gusset JointsTypes of Gusset Joints3636

SpecimensSpecimens

In-Plane Gusset

Out-of-Plane Gusset

7

3737

Welding Details of SpecimensWelding Details of Specimens

In-PlaneGusset

Out-of-PlaneGusset

3838

The Used SteelsThe Used Steels

HT80, SM570Q

3939

Stress Distribution at the End of Stress Distribution at the End of the Inthe In--Plane GussetsPlane Gussets

4040Stress Distribution at the End of Stress Distribution at the End of the Outthe Out--ofof--Plane GussetsPlane Gussets

4141

Fatigue Test Results Fatigue Test Results 4242

Fatigue Test Results Fatigue Test Results

In-PlaneIn-Plane

Effects of FinishingIn-Plane : Lower

8

4343

Fatigue Crack in InFatigue Crack in In--Plane Gusset Joints Plane Gusset Joints

Fatigue Strength:Category B

4444


Fatigue Strength:Category A

4545


Fatigue Strength:Category C and D

4646

Fatigue Crack in OutFatigue Crack in Out--ofof--Plane Gusset Joints Plane Gusset Joints

Fatigue Strength:Category D

From Root

4747

Fatigue Strength:Category C


The Unfused Partof the Root

4848

Fatigue Strength:Category E


This Type was not usedin the Honshu-Shikoku BridgeProject

9

4949

Size EffectsFull Size Fatigue Tests of Truss Chords

Topic 4

5050

Importance of Size Effects

Welded joint specimen

Large scaled specimen

Real scale floor beam of the Seto Bridge

5151

Girder specimen at Lehigh University in the US

5252

Full scale box section girder specimen of the Kurushima Bridge

5353

Full Size Fatigue Tests of Truss Chords

Minato Ohashi

Constructed in 1974(235m+510m+235m)

Outside: Partially Penetrated Groove WeldsInside: Fillet Welds

The Corner Joints of Truss Chords

5454

The Full Size Specimen of Truss Chords

4 Point Bending Tests

10

5555

The Full Size Specimen of Truss Chords5656

The Used Steels

600MPa Class SteelsThickness = 40, 60mm

5757

The Welding Condition of The Corner Joints5858

Fatigue Cracks in The Corner Joints (4 Types)

Fatigue Crack from Blowhole

Fatigue Crack from Stop-and-Startof Fillet Welding

5959

Type 1 Fatigue Crack Originated from a Blowhole 6060

Type 2 The Fatigue Crack Originated fromStop-and-Start Positions

Crack

A Stop-and-Start Position

11

6161

Type 2 The Fatigue Crack Originated fromStop-and-Start Positions

6262

Type 3 Collective Fatigue CracksAt the Roots of Fillet Welds

6363

Type 4 Fatigue CracksAlong the Fillet Weld-Beads

6464

Fatigue Test Results

Size Effects

6565

Consideration of Size Effects

Change of Fatigue Design Code Joint Type

Code Class Fatigue strengthat 2 million cycles (MPa)

Old code '60 D 120Current code '92 F 65

Sleeper pad Joint Type


Old code '60 D 100Current code '92 F 65

Out-plane gusset (t=20mm)

Joint Type


Old code '60 B 150Current code '92 C 125

Longitudinal welding

Joint Type


Old code '60 C 126Current code '92 F 65

In-plane gusset (t=20mm)

Joint Type


Old code '60 D 100Current code '92 E 80

Cruciform weld

6666

References1. Chitoshi Miki, Fumio Nishino, Yasuaki Hirabayashi, Koei Takena:

Influence of Residual Welding Stress on Fatigue Crack Growth Rate,Proc. of JSCE, No.330, 1983.2.

2. Chitoshi Miki, Fumio Nishino, Yasuaki Hirabayashi, Hiroyuki Ohga:Fatigue Strength of Longitudinal Welded Joints Containing Blowholes,Proc. of JSCE, No.325, 1982.9.

3. Chitoshi Miki, Fauzri Fahimuddin, Kengo Anami: Fatigue Strength of Butt-Welded Joints Containing Various Embedded Defects, Structural Eng./Earthquake Eng., JSCE, oNo.668/I-54, 2001.1.

4. Hirosuke Shimokawa, Koei Takena, Fumio Itoh, Chitoshi Miki:Fatigue Strength of Large Gusset Joints of 800MPa Class Steels,Proc. of JSCE, Vol.2, No.1, 1985.4.

5. Hirosuke Shimokawa, Koei Takena, Makoto Fukazawa, Chitoshi Miki:A Fatigue Test on the Full-Size Truss Chord,Proc. of JSCE, No.344/I-1, 1984.4.

fatigue strenght of welded joints

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