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1 Residual Stresses and Distortion in Weldments By: Aziz Shafiei Residual Stresses

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Page 1: Residual Stress & Distortion.ppt - mechshop.irmechshop.ir/.../2016/07/Residual-Stress-Distortion... · 2 Causes of Residual Stresses Residual stresses in metal structures occur for

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Residual Stresses and Distortion in Weldments

By: Aziz Shafiei

Residual Stresses

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Causes of Residual Stresses

Residual stresses in metal structures occur for manyreasons during various manufacturing stagesreasons during various manufacturing stages.

Residual stresses may be produced in manystructural elements, including plate, bar, andsections, during rolling, casting, or forging.

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They may occur during forming and shaping ofmetal parts by such processes as shearing,bending, machining, and grinding.

Development of Residual Stresses

Thermally induced

stresses:

(a)during heating;

(b)during cooling;

(c)residual stresses

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( )

in weld.

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Thermal Stresses During WeldingB

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Residual Stresses in a Butt Weld

Stress distribution is characterized by twoparameters: (1) the maximum stress at weldRegion (σm)(2) the width of the tensionzone of residual stress (b)

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In weldments made of low-carbon steel, the maximumresidual stress (σm) is usuallyas high as the yield stress ofthe weld metal.

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Measurement of residual stresses

A- Stress-relaxation

B- X-ray diffraction

C- Stress-sensitive property analysis

D- Cracking techniques

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Measurement of residual stresses

A- Stress-relaxation

B- X-ray diffraction

C- Stress-sensitive property analysis

D- Cracking techniques

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Measurement of residual stresses

A- Stress-relaxation

B- X-ray diffraction

C- Stress-sensitive property analysis

D- Cracking techniques

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Measurement of residual stresses

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Stress-relaxation Techniques

Elastic strain release is measured todetermine residual stresses in stress-determine residual stresses in stress-relaxation analysis.

Residual stress is relaxed by removing apiece from the specimen, or by cutting thespecimen into pieces.

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specimen into pieces.

Generally, strain release is measured withelectric or mechanical strain gages.

Stress-relaxation Techniques

Stress-relaxation techniques are widely usedto measure residual stress in weldmentsto measure residual stress in weldments,because they produce reliable andquantitative data.

However, stress-relaxation techniques aredestructive.

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destructive.

The specimen must be sectioned either partlyor entirely.

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Stress-relaxation Techniques

Five techniques for measuring residual stresses,based on stress-relaxation techniques that can be

fused for weldments, are:

Sectioning Technique Using Strain Gages.

Mathar-Soete Drilling Technique.

The Gunnert Drilling Technique.or m

echa

nica

l ai

n ga

ges

PLATE

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The Gunnert Drilling Technique.

Rosenthal-Norton Sectioning Technique.

Photoelastic Coating-Drilling Technique.

Ela

stic

st

ra

3D SOLIDS

Stress-relaxation Techniques

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Stress-relaxation TechniquesB

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Stress-relaxation Techniques

Mathar-Soete Drilling Technique.

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Stress-relaxation Techniques

Rosenthal-Norton Sectioning Technique.

This technique proposed a technique for determining residualstresses in heavy weldments.

Two narrow blocks with full thickness of the plate, one parallel to theweld and the other transverse to the weld, are cut from the weld.

Residual stress remaining in the narrow blocks is then measured.

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Formulas have been proposed to estimate residual stresses in theinterior of the weldment from strain changes that occur while cuttingthe narrow blocks and residual stresses that are left in the blocks.

Stress-relaxation Techniques

Photoelastic Coating-Drilling Technique.

Using this method, a hole is drilled to a certain depth (forinstance, equal to the diameter) at the measuring pointthrough the photoelastic coating and a portion of thespecimen.

Birefringence occurs in areas near the drilled hole if residualstresses exist.

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By analysis, the birefringence strain release that took placeduring drilling is determined.

Then the residual stresses that existed in the drilled area arecalculated.

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X-ray Techniques

Elastic strains can be determinednondestructively (without machining ornondestructively (without machining ordrilling).

This is the only technique suitable formeasuring residual stresses in applicationssuch as gear teeth and ball bearings.

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such as gear teeth and ball bearings.

It also is suitable for measuring residualsurface stress after machining or grinding.

X-ray Techniques

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Drawbacks X-ray Techniques

They are slow processes.

Measurements must be made in two directions ateach measuring point.

Each measurement requires 15 to 30 min ofexposure for the film technique.

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Measurements are not very accurate, particularlywith heat treated materials in which atomicstructures are distorted.

Hardness Testing Techniques

Hardness testing techniques use stressinduced changes in hardnessinduced changes in hardness.

These techniques have not been developedpast the laboratory stage, and none has beenused with success for measuring residual

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stresses in weldments.

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Cracking Techniques

Residual stresses can be studied by observingcracks in specimens produced by residual stresses.c ac s spec e s p oduced by es dua st essesThese cracks may be induced by the presence ofhydrogen or stress corrosion.

In studying complex structural models that havecomplicated residual stress distributions, thesecracking techniques have been useful.

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g q

These techniques result in qualitative rather thanquantitative data.

Distribution of Residual Stress in Weldments

Pl W ldPlug Weld.

Welded Shapes and Columns. I

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Welded Pipe.

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Distribution of Residual Stress in Weldments

Plug Weld.

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Distribution of Residual Stress in Weldments

Welded Shapes and Columns.

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Distribution of Residual Stress in Weldments

Welded Shapes and Columns.

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Distribution of Residual Stress in Weldments

Welded Pipe.

Distribution of residual stresses is affectedby:

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by:Diameter and wall thickness of the pipeJoint design (square butt, V, X, etc.)Welding procedure and sequence(welded on outside only, welded on bothsides, outside first, or welded on bothsides, inside first)

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Distribution of Residual Stress in Weldments

Welded Pipe.

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Residual Stress in Weldments in Various Materials

In welding low-carbon steel thecarbon steel, themaximum residualstress in the weld isas high as the yieldstress of thematerial

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material.

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Residual Stress in Weldments in Various Materials

The magnitude and distribution of residualstress are affected by:stress are affected by:

Temperature distribution in the weldment.

Thermal expansion characteristics of the material.

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Mechanical properties of the material at room andelevated temperatures.

Residual Stress in Weldments in Various Materials

Comparison of some physical propertiesof steel aluminum and titaniumof steel, aluminum, and titanium

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Residual Stress in Weldments in Various MaterialsB

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Residual Stress in Weldments in Various Materials

Maximum mechanical strains

observed at locations 1 in. from

weld line (μin./in.) versus yield

t th (k i) f th b l t

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strength (ksi) of the base plate.

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Residual Stress in Weldments in Various Materials

Welds in High-Strength Steels.

Welds in Aluminum Alloys.

Welds in Titanium Alloys.

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Residual Stress in Weldments in Various Materials

Welds in High-Strength Steels.

Are peak values of residual stresses as high as the yieldstresses of the weld metal and base metal?

How wide are the areas with high tensile residual stresses?

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Residual Stress in Weldments in Various Materials

Welds in High-Strength Steels.

Distribution of longitudinal

residual stresses in a butt

weld in high-strength steel

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weld in high strength steel.

Residual Stress in Weldments in Various Materials

Welds in Aluminum Alloys.

Distribution of yield

strength and longitudinal

residual stresses in a

welded 5456-H321 plate 36

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in. wide and 1/2 in. thick.

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Residual Stress in Weldments in Various Materials

Welds in Titanium Alloys.

Distribution of residual stresses in

weldment of Ti-6Al-2Nb-1Ta-1Mo alloy

made by gas metal arc welding

(GMAW), using Ti-6A1-2Nb-1Ta-0.8Mo

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filler wire.

Effects of Specimen Size on Residual Stress

When measuring residual stress in a weldment, welded specimens

Effect of Specimen Length.

must be large enough to contain residual stresses as high as

those that exist in actual structures.

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g

Effect of Specimen Width.

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Effects of Specimen Size on Residual Stress

Effect of Specimen Length.Longitudinal residual stress valuesmust be zero at both ends of theweld, while high tensile stresses existin the central region.

The peak stress in the central regionincreases with increasing weld length.

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Effects of Specimen Size on Residual Stress

Effect of Specimen Length.Longitudinal residual stress valuesmust be zero at both ends of theweld, while high tensile stresses existin the central region.

The peak stress in the central regionincreases with increasing weld length.

Welds longer than 18 in are needed

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Welds longer than 18 in. are neededto produce high tensile stresses in thelongitudinal direction.

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Effects of Specimen Size on Residual Stress

Effect of Specimen Length.Longitudinal residual stress valuesmust be zero at both ends of theweld, while high tensile stresses existin the central region.

The peak stress in the central regionincreases with increasing weld length.

Welds longer than 18 in are needed

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Welds longer than 18 in. are neededto produce high tensile stresses in thelongitudinal direction.

In welds longer than 18 in.,longitudinal residual stresses in thecentral region became uniform.

Distortion

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Distortion in Weldments

During heating and cooling in the welding cycle,thermal strains accurse in the weld metal and base-

l i h ldmetal regions near the weld.

The strains produced during heating areaccompanied by plastic upsetting.

The stresses resulting from these strains combineand react to produce internal forces that cause

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and react to produce internal forces that causebending, buckling, and rotation.

It is these displacements that are called distortion.

Fundamental Types of Distortion

Transverse shrinkage perpendicular to theweld lineweld line.

Longitudinal shrinkage parallel to the weldline.

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Angular distortion (rotation around the weldline).

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Distortion in welded structuresB

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Slide 7

Slide 7

Distortion in Weldments

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Transverse Shrinkage of Butt Welds

Major factors causing non-uniform transverseshrinkage in butt welds are:shrinkage in butt welds are:

Rotational Distortion.

Joint Restraint.

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Slide 64

Transverse Shrinkage of Butt Welds

Major factors causing non-uniform transverseshrinkage in butt welds are:shrinkage in butt welds are:

Rotational Distortion.

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The rotational distortion is affected by welding heat input and the location of tack welds.

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Formulas for Transverse Shrinkage

Spraragen and Ettinger.

S is transverse shrinkage, in.A, is cross-sectional area of weld, in.2

t is thickness of plates, in.d is free distance or root opening, in.

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Formulas for Transverse Shrinkage

Capel.

Δl is transverse shrinkage, in.s is thickness of layer of weld metal, in.u is welding speed, in./minW is electric power of welding arc, W

p

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60˚ V

-gro

ove,

w

ithou

t a ro

ot g

a p GTAW

SMAW

SMAW

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Formulas for Transverse Shrinkage

Capel.

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Mechanisms of Transverse Shrinkage

The major portion of transverse shrinkage ofa butt weld is due to contraction of the basea butt weld is due to contraction of the baseplate.

Shrinkage of the weld metal is only about10% of the actual shrinkage.

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Mechanisms of Transverse Shrinkage

δs: Thermal expansion of the basemetal at t = tmetal at t = ts

δ: Additional thermal deformation ofthe base metal caused in AA' at t > ts

Sw: Thermal contraction of the weldmetal at t > ts

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Mechanisms of Transverse Shrinkage

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Transverse Shrinkage During multipass WeldingB

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Transverse Shrinkage During multipass Welding

Three methods to reduce transverse shrinkage:

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Transverse Shrinkage During multipass Welding

The effects of various factors on transverse shrinkage,including:

Root opening

Joint design

Type and size of electrodes

Gre

ates

t Effe

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Heat input

0

Effect of Welding Sequence on Transverse Shrinkage

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Effect of Restraint on Transverse ShrinkageB

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Effect of Restraint on Transverse Shrinkage

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Effect of Restraint on Transverse Shrinkage

Slit-type specimen.

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Effect of Restraint on Transverse Shrinkage

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Circular-ring type specimen.

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Longitudinal Shrinkage of Butt Welds

The amount of longitudinal shrinkage in a butt weldis on the order of I/I000 of the weld length muchis on the order of I/I000 of the weld length, muchless than the transverse shrinkage.

I is the welding current, A

L is the length of weld, in.

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t is the plate thickness,in.

Slide 64

Longitudinal Shrinkage of Fillet Welds

As plate width and thickness

increase, restraint is more

effective. Therefore, total cross

section of the welded plate in

the transverse section is called

the "resisting cross section".

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For Ap to Aw is less than 20:

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Angular Change in Fillet WeldsB

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Φ<Φ0

Angular Change in Fillet Welds

Φ<Φ0

Ri idit f th b tt l t

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Rigidity of the bottom plate:

Angular rigidity coefficient:

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Angular Change in Fillet Welds

Values of angular rigidity coefficient C for low-carbon steel

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Angular Change in Fillet Welds

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Angular Change in Fillet WeldsB

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Angular Change in Fillet Welds

Values of angular rigidity coefficient C for 5086-H32 aluminum alloy

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5086-H32 was gas metal arc welded with alloy 5356 filler wire.

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Angular Change in Fillet WeldsB

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Angular Change in Fillet Welds

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Angular Change in Fillet WeldsB

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Bending Distortion Produced by Longitudinal Shrinkage

T-beams were fabricated by fillet

welding a web plate 4 or 6 in.

high to a flange plate 4 in. wide.

The 5052-H32 alloy plates were

0.5 in. thick and 48 in. long; they

were welded by GMAW using

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were welded by GMAW using

4043 and 2319 filler wires.

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Buckling DistortionB

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Buckling Distortion

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Comparison of Distortion in Aluminum and Steel Weldments

The value of thermal conductivity of aluminum isabout five times that of steel.

The coefficient of linear thermal expansion ofaluminum is about two times that of steel.

The value of Young's modulus of aluminum is aboutone third that of steel.

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Comparison of Distortion in Aluminum and Steel Weldments

Transverse Shrinkage of a Butt Weld.

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Comparison of Distortion in Aluminum and Steel Weldments

Angular Change of a Fillet Weld.

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Comparison of Distortion in Aluminum and Steel Weldments

Longitudinal Distortion.

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Effects of Residual Stresses

and

Distortion on Service Behavior

of Welded Structures

Changes of Residual Stresses in Weldments Subjected to Tensile Loading

The stressdistribution

h ld

As the level ofloading increases,h id lacross the weld

becomes moreeven as the levelof applied stressincreases.

the residual stressdistribution afterunloadingbecomes moreeven.

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As the level of applied stress increases, theeffect of residual stress decreases.

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Effects of Residual Stresses on Brittle Fractures of Welded Structures

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Effect of Stress-Relieving Treatments on Brittle Fracture of Weldments

Mechanical Stress Reliving

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Effect of Stress-Relieving Treatments on Brittle Fracture of Weldments

Thermal Stress Reliving

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Effects of Residual Stresses on Fatigue Fracture of Welded Structures

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Buckling Under Compressive LoadingB

y: A

. Sha

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Buckling Under Compressive Loading

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Buckling Under Compressive Loading

Combined Effects of Residual Stresses andDistortion.Distortion.

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Buckling Under Compressive Loading

Combined Effects of Residual Stresses andDistortion.Distortion.

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