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Relating Radial Strain to Circumferential 
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#1
Feb1211, 12:10 PM

P: 1

Hi,
I have a solid cylinder to which I have strain gauges attached to measure axial and circumferential strains. My goal is to relate the circumferential strain to radial strain and then to calculate possion's ratio. Every time I try to work out the geometry of the problem I end up saying that circumferential strain is equal to axial strain, can this be true? Terms: Ec = Circumferential Strain = dC/C dC = change in length of circumference C = circumference Er = Radial Strain = dR/R dR = change in length of radius R = radius Here is my logic: Strain Circumferential (Ec) is equal to the strain is see in one single strain gauge attached along circumference. dC = 2*PI*dR. Then dR can be expressed as dR = C*Ec/(2*PI). Which means Er= dR/R = C*Ec/(2*PI*R) = Ec. Can that be right? Then is my possion's ratio radial/axial or axial/radial? Thanks. 


#2
Feb1411, 08:12 AM

P: 343

You're right about the radial strain being equal to the circumferential strain. Since circumference changes proportionally with radius, the strains will be the same since strain is really just a proportion.
However, you're not taking axial strain into consideration. Your axial strain will be dL/L. The Poisson's ratio is v=Er/Ea = (dR/R)/(dL/L) or (dC/C)/(dL/L) if you prefer. 


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