Upload
others
View
28
Download
3
Embed Size (px)
Citation preview
1
Residual Stresses and Distortion in Weldments
By: Aziz Shafiei
Residual Stresses
2
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.
By:
A. S
hafie
i
3 of 92
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
By:
A. S
hafie
i
4 of 92
( )
in weld.
3
Thermal Stresses During WeldingB
y: A
. Sha
fiei
5 of 92
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)
By:
A. S
hafie
i
6 of 92
In weldments made of low-carbon steel, the maximumresidual stress (σm) is usuallyas high as the yield stress ofthe weld metal.
4
Measurement of residual stresses
A- Stress-relaxation
B- X-ray diffraction
C- Stress-sensitive property analysis
D- Cracking techniques
By:
A. S
hafie
i
7 of 92
Measurement of residual stresses
A- Stress-relaxation
B- X-ray diffraction
C- Stress-sensitive property analysis
D- Cracking techniques
By:
A. S
hafie
i
8 of 92
5
Measurement of residual stresses
A- Stress-relaxation
B- X-ray diffraction
C- Stress-sensitive property analysis
D- Cracking techniques
By:
A. S
hafie
i
9 of 92
Measurement of residual stresses
By:
A. S
hafie
i
10 of 92
6
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.
By:
A. S
hafie
i
11 of 92
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.
By:
A. S
hafie
i
12 of 92
destructive.
The specimen must be sectioned either partlyor entirely.
7
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
By:
A. S
hafie
i
13 of 92
The Gunnert Drilling Technique.
Rosenthal-Norton Sectioning Technique.
Photoelastic Coating-Drilling Technique.
Ela
stic
st
ra
3D SOLIDS
Stress-relaxation Techniques
By:
A. S
hafie
i
14 of 92
8
Stress-relaxation TechniquesB
y: A
. Sha
fiei
15 of 92
Stress-relaxation Techniques
Mathar-Soete Drilling Technique.
By:
A. S
hafie
i
16 of 92
9
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.
By:
A. S
hafie
i
17 of 92
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.
By:
A. S
hafie
i
18 of 92
By analysis, the birefringence strain release that took placeduring drilling is determined.
Then the residual stresses that existed in the drilled area arecalculated.
10
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.
By:
A. S
hafie
i
19 of 92
such as gear teeth and ball bearings.
It also is suitable for measuring residualsurface stress after machining or grinding.
X-ray Techniques
By:
A. S
hafie
i
20 of 92
11
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.
By:
A. S
hafie
i
21 of 92
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
By:
A. S
hafie
i
22 of 92
stresses in weldments.
12
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.
By:
A. S
hafie
i
23 of 92
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
By:
A. S
hafie
i
24 of 92
Welded Pipe.
13
Distribution of Residual Stress in Weldments
Plug Weld.
By:
A. S
hafie
i
25 of 92
Distribution of Residual Stress in Weldments
Welded Shapes and Columns.
By:
A. S
hafie
i
26 of 92
14
Distribution of Residual Stress in Weldments
Welded Shapes and Columns.
By:
A. S
hafie
i
27 of 92
Distribution of Residual Stress in Weldments
Welded Pipe.
Distribution of residual stresses is affectedby:
By:
A. S
hafie
i
28 of 92
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)
15
Distribution of Residual Stress in Weldments
Welded Pipe.
By:
A. S
hafie
i
29 of 92
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
By:
A. S
hafie
i
30 of 92
material.
16
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.
By:
A. S
hafie
i
31 of 92
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
By:
A. S
hafie
i
32 of 92
17
Residual Stress in Weldments in Various MaterialsB
y: A
. Sha
fiei
33 of 92
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
By:
A. S
hafie
i
34 of 92
strength (ksi) of the base plate.
18
Residual Stress in Weldments in Various Materials
Welds in High-Strength Steels.
Welds in Aluminum Alloys.
Welds in Titanium Alloys.
By:
A. S
hafie
i
35 of 92
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?
By:
A. S
hafie
i
36 of 92
19
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
By:
A. S
hafie
i
37 of 92
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
By:
A. S
hafie
i
38 of 92
in. wide and 1/2 in. thick.
20
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
By:
A. S
hafie
i
39 of 92
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.
By:
A. S
hafie
i
40 of 92
g
Effect of Specimen Width.
21
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.
By:
A. S
hafie
i
41 of 92
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
By:
A. S
hafie
i
42 of 92
Welds longer than 18 in. are neededto produce high tensile stresses in thelongitudinal direction.
22
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
By:
A. S
hafie
i
43 of 92
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
23
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
By:
A. S
hafie
i
45 of 92
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.
By:
A. S
hafie
i
46 of 92
Angular distortion (rotation around the weldline).
24
Distortion in welded structuresB
y: A
. Sha
fiei
47 of 92
Slide 7
Slide 7
Distortion in Weldments
By:
A. S
hafie
i
48 of 92
25
Transverse Shrinkage of Butt Welds
Major factors causing non-uniform transverseshrinkage in butt welds are:shrinkage in butt welds are:
Rotational Distortion.
Joint Restraint.
By:
A. S
hafie
i
49 of 92
Slide 64
Transverse Shrinkage of Butt Welds
Major factors causing non-uniform transverseshrinkage in butt welds are:shrinkage in butt welds are:
Rotational Distortion.
By:
A. S
hafie
i
50 of 92
The rotational distortion is affected by welding heat input and the location of tack welds.
26
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.
By:
A. S
hafie
i
51 of 92
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
By:
A. S
hafie
i
52 of 92
60˚ V
-gro
ove,
w
ithou
t a ro
ot g
a p GTAW
SMAW
SMAW
27
Formulas for Transverse Shrinkage
Capel.
By:
A. S
hafie
i
53 of 92
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.
By:
A. S
hafie
i
54 of 92
28
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
By:
A. S
hafie
i
55 of 92
Mechanisms of Transverse Shrinkage
By:
A. S
hafie
i
56 of 92
29
Transverse Shrinkage During multipass WeldingB
y: A
. Sha
fiei
57 of 92
Transverse Shrinkage During multipass Welding
Three methods to reduce transverse shrinkage:
By:
A. S
hafie
i
58 of 92
30
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
ctB
y: A
. Sha
fiei
59 of 92
Heat input
0
Effect of Welding Sequence on Transverse Shrinkage
By:
A. S
hafie
i
60 of 92
31
Effect of Restraint on Transverse ShrinkageB
y: A
. Sha
fiei
61 of 92
Effect of Restraint on Transverse Shrinkage
By:
A. S
hafie
i
62 of 92
32
Effect of Restraint on Transverse Shrinkage
Slit-type specimen.
By:
A. S
hafie
i
63 of 92
Effect of Restraint on Transverse Shrinkage
By:
A. S
hafie
i
64 of 92
Circular-ring type specimen.
33
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.
By:
A. S
hafie
i
65 of 92
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".
By:
A. S
hafie
i
66 of 92
For Ap to Aw is less than 20:
34
Angular Change in Fillet WeldsB
y: A
. Sha
fiei
67 of 92
Φ<Φ0
Angular Change in Fillet Welds
Φ<Φ0
Ri idit f th b tt l t
By:
A. S
hafie
i
68 of 92
Rigidity of the bottom plate:
Angular rigidity coefficient:
35
Angular Change in Fillet Welds
Values of angular rigidity coefficient C for low-carbon steel
By:
A. S
hafie
i
69 of 92
Angular Change in Fillet Welds
By:
A. S
hafie
i
70 of 92
36
Angular Change in Fillet WeldsB
y: A
. Sha
fiei
71 of 92
Angular Change in Fillet Welds
Values of angular rigidity coefficient C for 5086-H32 aluminum alloy
By:
A. S
hafie
i
72 of 92
5086-H32 was gas metal arc welded with alloy 5356 filler wire.
37
Angular Change in Fillet WeldsB
y: A
. Sha
fiei
73 of 92
Angular Change in Fillet Welds
By:
A. S
hafie
i
74 of 92
38
Angular Change in Fillet WeldsB
y: A
. Sha
fiei
75 of 92
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
By:
A. S
hafie
i
76 of 92
were welded by GMAW using
4043 and 2319 filler wires.
39
Buckling DistortionB
y: A
. Sha
fiei
77 of 92
Buckling Distortion
By:
A. S
hafie
i
78 of 92
40
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.
By:
A. S
hafie
i
79 of 92
Comparison of Distortion in Aluminum and Steel Weldments
Transverse Shrinkage of a Butt Weld.
By:
A. S
hafie
i
80 of 92
41
Comparison of Distortion in Aluminum and Steel Weldments
Angular Change of a Fillet Weld.
By:
A. S
hafie
i
81 of 92
Comparison of Distortion in Aluminum and Steel Weldments
Longitudinal Distortion.
By:
A. S
hafie
i
82 of 92
42
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.
By:
A. S
hafie
i
84 of 92
As the level of applied stress increases, theeffect of residual stress decreases.
43
Effects of Residual Stresses on Brittle Fractures of Welded Structures
By:
A. S
hafie
i
85 of 92
Effect of Stress-Relieving Treatments on Brittle Fracture of Weldments
Mechanical Stress Reliving
By:
A. S
hafie
i
86 of 92
44
Effect of Stress-Relieving Treatments on Brittle Fracture of Weldments
Thermal Stress Reliving
By:
A. S
hafie
i
87 of 92
Effects of Residual Stresses on Fatigue Fracture of Welded Structures
By:
A. S
hafie
i
88 of 92
45
Buckling Under Compressive LoadingB
y: A
. Sha
fiei
89 of 92
Buckling Under Compressive Loading
By:
A. S
hafie
i
90 of 92
46
Buckling Under Compressive Loading
Combined Effects of Residual Stresses andDistortion.Distortion.
By:
A. S
hafie
i
91 of 92
Buckling Under Compressive Loading
Combined Effects of Residual Stresses andDistortion.Distortion.
By:
A. S
hafie
i
92 of 92