Residual Stresses in Welded Elements:Measurements, Fatigue Analysis

and Beneficial Redistribution

Y. Kudryavtsev and J. KleimanStructural Integrity Technologies, Inc.

(SINTEC)

www.sintec.ca1

OUTLINE OF THE PRESENTATIONINTRODUCTION. RESIDUAL STRESS MANAGEMENT

MEASUREMENT OF RESIDUAL STRESSES BY ULTRASONIC METHOD (UM)

FATIGUE IMPROVEMENT BY ULTRASONIC IMPACT TREATMENT (UIT-UP)

EXAMPLES OF INDUSTRIAL APPLICATION OF UMAND UIT-UP

SUMMARY

Importance of Residual Stresses

Residual Stresses in Welded Elements

Distribution of longitudinal (along the weld) and transverse components of residual stresses along the butt weld toe

Effect of Residual Stresses

Fatigue curves of butt welded joint in low-carbon steel:1 - without residual stresses;

2,3 - with high tensile residual stresses (fatigue testing and computation)

Effect of Residual Stresses

Fatigue curves of non-load caring fillet welded joint in high strength steel:1 -in as welded condition;

2,3- after application of ultrasonic peening (fatigue testing and computation)

IMPORTANCE OF RESIDUAL STRESS MANAGEMENT

RESIDUAL STRESS ORIGINATED FROM:Differential plastic flow Differential cooling ratesPhase transformations with volume changes etc.

RESIDUAL STRESSES ARE CREATED BY:Welding Machining Forging Rolling Surface treatments Casting

Heat treatment

WHERE RESIDUAL STRESSES ARE IMPORTANT:Fatigue Life Corrosion ResistanceDimensional Stability Brittle FractureDistortion

RESIDUAL STRESS MANAGEMENT

is an important component of the process of

DESIGN, MANUFACTURING, MAINTENANCE and REPAIR

of PARTS and WELDED ELEMENTS

STAGES IN RESIDUAL STRESS (RS) STAGES IN RESIDUAL STRESS (RS) MANAGEMENTMANAGEMENT

Stage 1:Stage 1: RS DeterminationRS Determination- MEASUREMENT: Destructive, Non-Destructive

- COMPUTATION

Stage 2:Stage 2: RS Effect AnalysisRS Effect Analysis- EXPERIMENTAL STUDIES

- COMPUTATION

Stage 3:Stage 3: RS Modification (if required)RS Modification (if required)- CHANGES in TECHNOLOGY of MANUFACTORING / ASSEMBLY

- APPLICATION of STRESS - RELIEVING TECHNIQUES

RESIDUAL STRESS MANAGEMENTRESIDUAL STRESS MANAGEMENTProposed Complex of Advanced Engineering ToolsProposed Complex of Advanced Engineering Tools

Stage 1:Stage 1: RS DeterminationRS DeterminationUltrasonic Measurement of Applied and Residual Stresses (UM)

Device and Software – UltraMARS

Stage 2:Stage 2: RS Effect AnalysisRS Effect AnalysisExpert System for Fatigue Assessment and Optimization

of Parts and Welded Elements - RESIsT

Stage 3:Stage 3: RS Modification (if required)RS Modification (if required)Ultrasonic Peening of Parts and Welded Elements (UP/UIT)

Equipment and Software – UltraPeen

The Ultrasonic Computerized Complex for measurement

of residual and applied stresses - UltraMARS

Ultrasonic Method of Residual Stress MeasurementUltrasonic stress measurement techniques are based on the acoustic-

elasticity effect, according to which the velocity of elastic wave propagation in solids is dependent on the mechanical stress

∆C/C •10-3

σ, MPasteel A (1) steel B (2) aluminum alloy (3)

● - C SX3 ; ○ - C SX2 ; x - C L

Acoustic-Elastic Relationships

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+><+><

++=

µλσµ

µλσσλ

µλµσµλ

µλσ

242(

)2(3)(

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)2(3)(2

011

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+= 011

033

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32

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3σ

µσ

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µµλ

µσ c

KKKbCCC kk

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Clx1 – is the longitudinal wave propagation velocity, Csx2 and Csx3 – are the polarized shear wave propagation velocities, σ0

11, σ022 and σ0

33 – are the residual stresses in the corresponding directions,ρ, λ, µ, a, b, c and K0 – are material constants

The main technical characteristics of UltraMARS measurement system:

- stress can be measured in materials with thickness 2 - 150 mm;

- error of stress determination (from external load): 5 - 10 MPa;

- error of residual stress determination: 0.1 σy (yield strength) MPa;

- stress, strain and force measurement in fasteners (pins) 25-1000 mm;

- independent power supply (accumulator battery 12 V);

- overall dimensions of measurement device: 300x200x150 mm;

- weight of unit with sensors: 7 kg.

PRESENTATION OF THE RESIDUAL STRESS MEASUREMENT DATA USING THE DEVELOPED SOFTWARE

Distribution of residual stresses in a low carbon steel plate after local heating

Measurement of Residual Stresses by Ultrasonic Method in Shipbuilding Applications

The process of RS measurement in welded samples and panel before fatigue testing

RS measurement at different locations (Line 2, 3, 4, 5 and 6) of welded panel after 1, 2, 10 and 2000 cycles of loading

Distribution of RS near the end of stiffener

Distribution of RS in welded ample along lines 1 and 2.1

0 10 20 30 40 50 60 70 80

-160

-120

-80

-40

0

40

80

120

160

200

240

280

320

σ22

σ33

Res

idua

l S

tress

es,

MP

a

Distance from the Weld, mm0 10 20 30 40 50 60 70

-240

-200

-160

-120

-80

-40

0

40

80

120

160

200

240

280

320

σ22

σ33

Res

idua

l S

tress

es,

MP

a

Distance L, mm

Measurement of Residual Stresses in a Welded Bridge

Residual Stress Measurement in One of the Welded Elements of the Pressure Hull of Submarine

RESIDUAL STRESS MANAGEMENTExpert SystemExpert System for for Fatigue AssessmentFatigue Assessment and and OptimizationOptimization

of Parts and Welded Elements of Parts and Welded Elements -- RESIsTRESIsTThe RESIsT is an Expert System for optimization of welded elements and structures by fatigue criterion. The following important parameters of welded structures with the goal to enhance the fatigue performance are analyzed:

• preferred design of parts and welded elements;

• material selection;

• welding and other technological processes;

• residual stresses;

• application of improvement treatments;

• influence of possible repair technologies;

• realistic service conditions.

Residual Stress in Fatigue Analysis

Fatigue curves of transverse loaded butt weld at R=0: 1 - with high tensile residual stresses; 2, 3, 4, 5 and 6 - with residual stresses

equals to 0 MPa, 200 MPa, 100 MPa, -100 MPa and -200 MPa

Technology and Equipment for Ultrasonic Peening (UP) of Welded elements

Replaceable working headsfor different industrial applications

PRINCIPLE OF ULTRASONIC PEENING

The technique is based on the combined effect of the:

1. High frequency impacts of the special strikersand

2. Ultrasonic oscillation in treated material.

The view of the butt welds in as-welded condition (left side sample) and

after application of UP (right side sample)

The view of the fillet welds in as-welded condition (left side sample) and

after application of UP (right side sample)

30mm 15mm

Effectiveness of UP in Manufacturing and Repair

Fatigue curves of welded element (transverse non-load-carrying attachment):1 – in as welded condition, 2 – UP was applied before fatigue testing,

3 – UP was applied after fatigue loading with the number of cycles corresponding to 50% of expected fatigue life of samples in as-welded condition.

105 106

100

150

200

250

298765432

2

3

1

σ max

, MP

a

N, cycles

Effect of UP Treatment on Corrosion of Metals

A2 Steel

HSLA Material

Not treated by UP After UP treatment

Not treated by UP After UP treatment

The Advantages of UP:High (highest) efficiency Quick (treatment speed of ~ 0.5 m of weld/min)Considerably reduced vibrations and noise levels, easier in use than for example hammer peeningDeeper penetrationComputer controllableRobotic line - ready Lighter with no need in forced water-cooling as compared with similar magnetostrictivesystems.

Use of basic UP system for fatigue life improvement of tubular welded joint

UP system installed on a robot for automotive application

Ultrasonic Peening of Welded Bridges

Rehabilitation of Welded Bridge by Ultrasonic Peening (Indiana, USA)

Total Length of UP Treated Welds - 500 metersNumber of UP Treated Welded Elements -2500

Application of UP for Rehabilitation of Mining Equipment

UP of Fatigue Critical Welds of a Grinding Mill

Application of UP for Rehabilitation of Stamping Equipment

UP of a Welded Reinforcement

Plate

SUMMARY

1. Residual stresses play an important role in operating performance of materials, parts and structural elements. Their effect on the engineering properties of materials such as fatigue and fracture, corrosion resistance and dimensional stability can be considerable. The residual stresses, therefore, should be taken into account during design, fatigue assessment and manufacturing of parts and welded elements.

SUMMARY (continued)

2. The developed advanced ultrasonic method (UM), based on it portable instrument and the supporting software can be used for non-destructive residual stress analysis in laboratory samples and real structure elements in many applications for a wide range of materials. The developed ultrasonic technique was applied in construction industry, shipbuilding, railway and highway bridges, aerospace industry, oil and gas engineering and in other areas during manufacturing, in service inspection and repair of real parts and structures

SUMMARY (continued)

3. Ultrasonic Peening (UP/UIT) is a promising technique for fatigue life improvement and could be efficiently used for manufacturing, rehabilitation and repair of welded elements and structures. The developed computerized complex for UP was successfully applied in different applications for increasing of the fatigue life of welded elements, elimination of distortions caused by welding and other technological processes, residual stress relieving, increasing of the hardness of the surface of materials and surface nanocrystallization.