6 residual stresses and distortion

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Residual Stresses and Distortion


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Residual Stresses and Distortion

Lesson Objectives

When you finish this lesson you will

understand:• the generation of residual stress and

distortion in welds

• mechanisms to reduce residual stress

Learning Activities

1. Read Handbook

pp 21822!

2. "iew #lides$%. Read &otes'

(. )isten to lecture

*. +o online

workbook

Keywords

,hermal -pansion /oefficient' Residual #tress' +istortion'

#tressRelief

http://we019.eng.ohio-state.edu/wenc/wenc.cfmhttp://we019.eng.ohio-state.edu/we300/w300t/we300.htm


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Welding +esignWelding design involves consideration

of strength requirements cost and

service conditions

0 !echanical " #hysical $ro$erties

0 %oint Design 0 Welding stress and distortion

0.1.1.3.0.T1.95.12

&overed

'arlier


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T ∆=α ε


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Residual #tress +istortion in Welds

• Heat flows from the weld area and causing

the oint area to epand (See #revious !odule)

• ,hermal epansion and contraction due to

welding can lea3e behind permanent stress

and distortion

• Higher heat input welds are more prone to

residual stress and distortion

• 4ncreased restraint can decrease distortion

but can result in higher residual stress

Residual Stress and Distortion

0.1.1.3.3.T18.95.12


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Residual #tress 5attern• Residual stress is

present across an

unrestrained butt weldafter cooling

• ,ension near weld bead

• /ompression away

from the weld bead

• Restraint can affect this

stress stateCompression

Tension



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*urn to the $erson sitting ne+t to you and discuss (, min-).

• We have seen from the metallurgy module that dislocation

tangles and $ile/u$s occurring above the yield strength of

materials cause the higher stresses- We have seen here that

by a tem$erature cycle that varies across the $late we have

regions that yield and residual stresses occur- We have seen

that im$osing o$erating stresses above yield cause changesin the residual stress distribution by movement of the

dislocations- 0ow else then might we get rid of some of

these dislocations to remove these residual stresses1


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,ypes of +istortion


0.1.1.3.3.T19.95.12


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+istortion

Transverse Shrinkage

Rotational Distortion Longitudinal Bending Buckling

Longitudinal Shrinkage Angular Change



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-liminating +istortion

• 5reset members to

counteract distortion

• 6itures to clampworkpiece in place

0 Restraint reduces

distortion but increases

residual stress

• #tressrelief heat

treatment

Angular distortion after welding

Preset members before welding


6 residual stresses and distortion

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