Weld Design and


Download 0.7 Mb.
Pdf ko'rish
Sana05.10.2020
Hajmi0.7 Mb.

1

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

jglancey@udel.edu

jglancey@udel.edu

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

I

I



Strength (static and/or fatigue)

Strength (static and/or fatigue)

I

I

Material and the effects of heating



Material and the effects of heating

I

I



Cost

Cost


I

I

Distortion



Distortion

I

I



Residual Stresses

Residual Stresses

I

I

Easy to Weld



Easy to Weld

Static Strength

Static Strength

I

Stress - strain diagram



Strain (

ε)  = 



Stress (

σ)





F

A

∆ L



L

yield

ultimate

(tensile)

F

F

A

L

3

Shear Strength

Shear Strength

I

In general, material fails in shear due to 



distortion (at a molecular level)

I

Criteria for failure:



Ductile:  Shear Strength ~ 0.5 Tensile Strength

Brittle:   Shear Strength ~ 0.75 Tensile Strength



I

Weld strength analysis is generally based on 

Shear Strength


4

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


6

Endurance Limit

Endurance Limit

I

I



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.

I

I



For Aluminum:

For Aluminum:



No endurance limit (cannot have an infinite 



No endurance limit (cannot have an infinite 

life)


life)

7

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

8

Strength Considerations

Strength Considerations

I

Try to minimize the stresses in welds; make 



the parent materials carry highest stresses.

I

Butt welds are the most efficient



I

Avoid stress concentrations

I

Intermittent weld length should be at least 4 



times the fillet size

I

Minimize weld size to reduce potential for 



fatigue failure

9

Effects of Welding on Metallurgy

Effects of Welding on Metallurgy

I

I



Depends on the alloy and welding process

Depends on the alloy and welding process

I

I

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

10

Reducing Distortion

Reducing Distortion

I

Prevent overwelding



I

Intermittent welding

I

Minimize number of passes



I

Place welds near the neutral axis of the part

I

Balance welds around the neutral axis



I

Anticipate shrinkage forces

I

Residual stress relief



11

Neutral Axis

Neutral Axis

I

I



The line (plane) where bending stresses are 

The line (plane) where bending stresses are 



zero.

zero.


12

13

Download 0.7 Mb.

Do'stlaringiz bilan baham:




Ma'lumotlar bazasi mualliflik huquqi bilan himoyalangan ©fayllar.org 2020
ma'muriyatiga murojaat qiling