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prosenjit333
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Why Thermal Stress in a Bar is not Dependent Upon the Cross Section Area of the Bar

07/23/2015 2:55 AM

Hello friends,

i have read the thermal stress in beam but I cant understand why thermal stress in a bar is not depend upon the cross-sectional area of the bar?

Thank you for your answers

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IdeaSmith
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#1

Re: Why thermal stress in a bar is not depend upon the cross section area of the bar

07/23/2015 3:40 AM

You might want to look into this one here.

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prosenjit333
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#2
In reply to #1

Re: Why thermal stress in a bar is not depend upon the cross section area of the bar

07/23/2015 4:06 AM

sorry i cant find thermal stress.Can you discuss it, why it is not depend on area?
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IdeaSmith
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#13
In reply to #2

Re: Why thermal stress in a bar is not depend upon the cross section area of the bar

07/25/2015 4:19 AM

https://en.wikipedia.org/wiki/Stress_(mechanics)

Take note of the unit of Stress. It is a unit that has the area already included.

Same as pressure.

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Tornado
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#3

Re: Why thermal stress in a bar is not depend upon the cross section area of the bar

07/23/2015 4:09 AM

Because of all the dimensional units that cancel out in the calculations.

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prosenjit333
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#4
In reply to #3

Re: Why thermal stress in a bar is not depend upon the cross section area of the bar

07/23/2015 4:21 AM

thanks tornado but still I cant understand.

the thermal stress=E α t where

E= young's modulus

α= co-efficient of linear expansion

t= rise or drop in temparature..

by this formula we can say..thermal stress=F/A x l/Δl x α t

so this formula clearly shows that "Thermal stress depend on cross-sectional area"

Then why it is called, thermal stress does not depend upon cross-sectional area of a bar.

Please elaborate in detail because my brain is not so sharp.
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Tornado
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#5
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Re: Why thermal stress in a bar is not depend upon the cross section area of the bar

07/23/2015 5:04 AM

Because force and stress are not the same. Stress is force per unit area, and when you divide by area, the area units cancel.

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prosenjit333
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#6
In reply to #5

Re: Why thermal stress in a bar is not depend upon the cross section area of the bar

07/23/2015 5:34 AM

stress is force per unit area , if i divide by are there will be area square. How it is canceling?
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Codemaster
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#8
In reply to #6

Re: Why thermal stress in a bar is not depend upon the cross section area of the bar

07/23/2015 8:42 AM

In your #4 you say

the thermal stress = E α t where

E= young's modulus

α= co-efficient of linear expansion

t= rise or drop in temparature.

That's wrong, thermal strain, Δl/l = σ*t if the bar is not constrained in length. If it is constrained in length the stress = E*strain = E*Δl/l = E*σ*t. That's the stress, N/mm2 or whatever, independent of area. If you want the force, N, this = stress*area.

You're confusing stress and force, as Tornado tried to explain.

thermal stress=F/A x l/Δl x α t doesn't make sense.

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prosenjit333
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#9
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Re: Why thermal stress in a bar is not depend upon the cross section area of the bar

07/23/2015 1:03 PM

thanks to all for clear my confusion...tons of thanks to you guys
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PWSlack
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#10
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Re: Why thermal stress in a bar is not depend upon the cross section area of the bar

07/23/2015 2:49 PM

Staying attentive during course lectures really pays dividends...

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old salt
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#12
In reply to #10

Re: Why thermal stress in a bar is not depend upon the cross section area of the bar

07/23/2015 11:11 PM

What do you do when the professor himself can't stay attentive? Forgot what he was lecturing on; would fall asleep standing up; forget where the chalk was even though it was in his hand; would forget that he was driving while driving a car; always wore loafers because he couldn't remember how to tie his shoes (his wife had to tie them if he wore lace ups); would walk out of the lecture saying enough for today after 5-10 minutes; would light up a cigarette but he forgot that he was a non-smoker; would forget how to use his old time calculator, the chug-a-chug-a-chug-a-chug mechanical type; and had to use a strap to keep his glasses on so he didn't lose them. How were we to pay attention when the professor couldn't even do it himself?

Otherwise when it came to a person who knew all about Mercury there was none smarter. The vapors of it in the lab for his PhD are what caused this affliction.

Good Luck, Old Salt

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lyn
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#7

Re: Why Thermal Stress in a Bar is not Dependent Upon the Cross Section Area of the Bar

07/23/2015 7:13 AM

Because it's not.

Just live with it.
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minmi
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#11
In reply to #7

Re: Why Thermal Stress in a Bar is not Dependent Upon the Cross Section Area of the Bar

07/23/2015 10:35 PM

Love the no- nonsense replies that Lyn can create to people who have one line of thought and will not balance all opinions
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Codemaster (1); IdeaSmith (2); lyn (1); minmi (1); old salt (1); prosenjit333 (4); PWSlack (1); Tornado (2)

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