engineering question

[Kaido]

Hey,

Just wondering if anyone would be able to help me out im trying to work out Hoop strain for on my labs for uni.

and i can't seems to find the method of working it out

I know that normal strain E = elongation/original length

but my question is relating to a thin wall cylinder with open ends and mohr's circle



any help would be great

[PatB]

Surely hoop strain in a thin walled cylinder is basically just tensile strain in the wall. That is, the circumference will increase in accordance with E, and so the diameter, being proportional to circumference, will also increase in accordance with E.

It's a long time since I did this stuff formally, but that's how I remember thinking of it.

Of course, Mohr's circle implies that torsion comes into this somewhere, at which point, I'm afraid, I'm buggered.

[Kaido]

Surely hoop strain in a thin walled cylinder is basically just tensile strain in the wall. That is, the circumference will increase in accordance with E, and so the diameter, being proportional to circumference, will also increase in accordance with E.

It's a long time since I did this stuff formally, but that's how I remember thinking of it.

Of course, Mohr's circle implies that torsion comes into this somewhere, at which point, I'm afraid, I'm buggered.

thanks for that Patb, i was thinking along the similar lines.

I have reading from 6 strain gauges,

and in my notes it mention i should plot hoop stresses v's hoop strains work out the gradient and that will be an est of E.

However im confused as i have a equation for hoop stress. and im not sure if i just take the reading from gauge 1 (y direction) as the hoop strain.

For some reason i have written down Hoop Strain = stress x E however the whole point of the exerices is to work out E from the experimental data (strain gauge readings)

[Argon]

ha ha, I got that lab report somewhere if you want it

Is that with Kian Teh?

[PatB]

OK, I'm assuming the experimental setup to be a cylindrical pressure vessel, in which you vary the applied pressure and read strain from the strain gauges.

If that's so, being an Occam's Razor kind of chap, I can't see any reason to need the readings from any of the SGs apart from the one measuring circumferentially.

Stress is easy to work out, based on the pressure in the vessel, the longitudinal cross sectional area and the vessel length and wall thickness (hmm...if you haven't got a wall thickness, that complicates matters). Since E=Stress/Strain, it's then a simple matter to find E. Or, doing it graphically, if you plot stress up the y axis and strain along the x axis, the gradient of the graph will represent E.

[Kaido]

ha ha, I got that lab report somewhere if you want it

Is that with Kian Teh?

LOL yes it is =p

i'm just finishing up my conclusion now but wouldn't mind a look-see to see if i got everything right

OK, I'm assuming the experimental setup to be a cylindrical pressure vessel, in which you vary the applied pressure and read strain from the strain gauges.

If that's so, being an Occam's Razor kind of chap, I can't see any reason to need the readings from any of the SGs apart from the one measuring circumferentially.

Stress is easy to work out, based on the pressure in the vessel, the longitudinal cross sectional area and the vessel length and wall thickness (hmm...if you haven't got a wall thickness, that complicates matters). Since E=Stress/Strain, it's then a simple matter to find E. Or, doing it graphically, if you plot stress up the y axis and strain along the x axis, the gradient of the graph will represent E.

yeah i ended up confusing myself by some equations i wrote down that weren't needed. i just ended up plotting strees v's strain and found the gradient, which work out correct in the end.

[zed7fiddy]

ahh I remember that lab lol... if you still need a hand PM me.