Weld Design and

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Weld Design and 

Weld Design and 

Specification

Specification

Jim Glancey, PE

Jim Glancey, PE

Depts. of 

Depts. of 

Bioresources

Bioresources

Engineering 

Engineering 

& Mechanical Engineering

& Mechanical Engineering

University of Delaware

University of Delaware

[e-mail]

[e-mail]

http://

http://

udel.edu/~jglancey

udel.edu/~jglancey

I can’t explain everything . . .

I can’t explain everything . . .

4 in

6 in

1000 ft

Inside weld entire length

1/4”

2

Factors in Weld Design

Factors in Weld Design

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Strength (static and/or fatigue)

Strength (static and/or fatigue)

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Material and the effects of heating

Material and the effects of heating

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Cost

Cost

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Distortion

Distortion

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Residual Stresses

Residual Stresses

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Easy to Weld

Easy to Weld

Static Strength

Static Strength

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Stress - strain diagram

Strain (

ε)  = 

Stress (

σ)

= 

F

A

∆ L

L

yield

ultimate

(tensile)

F

F

A

L

3

Shear Strength

Shear Strength

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In general, material fails in shear due to 

distortion (at a molecular level)

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Criteria for failure:

•

Ductile:  Shear Strength ~ 0.5 Tensile Strength

•

Brittle:   Shear Strength ~ 0.75 Tensile Strength

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Weld strength analysis is generally based on 

Shear Strength

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Static Strength of Welds

Static Strength of Welds

F

F

Normal = 

Shear = 

F

w * h

F

w * h

2F

F

F

1/8

75

o

3/8

1/4

Max Normal = 

Max Shear = 

F

0.618w * h

F

0.707w * h

Butt

Fillet

h = throat size!

Weld Size vs. Throat Size

Weld Size vs. Throat Size

1/8

75

o

3/8

h = plate thickness = weld size

Butt

h = 0.707 * plate thickness

0.707 * weld size

1/4

Fillet

5

Fatigue Strength

Fatigue Strength

Cycles of Loading

Fatigue

Strength

1000

1,000,000

1

Endurance

Limit

Static Tensile Strength

Low

Cycle

High

Cycle

Infinite

Life

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Endurance Limit

Endurance Limit

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For Steel:

For Steel:

•

•

Endurance Limit = 0.5 * Tensile Strength

Endurance Limit = 0.5 * Tensile Strength

or 100 

or 100 

kpsi

kpsi

, which ever is lower.

, which ever is lower.

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For Aluminum:

For Aluminum:

•

•

No endurance limit (cannot have an infinite 

No endurance limit (cannot have an infinite 

life)

life)

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Factors for Fatigue Stress Analysis

Factors for Fatigue Stress Analysis

Type of Weld

Stress Increase

Butt Weld

1.2

Transverse Fillet

1.5

Parallel Fillet

2.7

T-butt with corners

2.0

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Strength Considerations

Strength Considerations

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Try to minimize the stresses in welds; make 

the parent materials carry highest stresses.

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Butt welds are the most efficient

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Avoid stress concentrations

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Intermittent weld length should be at least 4 

times the fillet size

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Minimize weld size to reduce potential for 

fatigue failure

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Effects of Welding on Metallurgy

Effects of Welding on Metallurgy

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Depends on the alloy and welding process

Depends on the alloy and welding process

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In general, cracking is promoted by:

In general, cracking is promoted by:

•

•

stress concentrations

stress concentrations

•

•

brittle parent material after welding (low      

brittle parent material after welding (low      

carbon steels)

carbon steels)

•

•

hydrogen in the weld metal

hydrogen in the weld metal

•

•

impurities in the weld metal

impurities in the weld metal

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Reducing Distortion

Reducing Distortion

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Prevent overwelding

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Intermittent welding

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Minimize number of passes

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Place welds near the neutral axis of the part

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Balance welds around the neutral axis

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Anticipate shrinkage forces

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Residual stress relief

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Neutral Axis

Neutral Axis

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The line (plane) where bending stresses are 

The line (plane) where bending stresses are 

zero.

zero.

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