Sorry Andy was in a rush before...
not a problem mate
Area = Pi x Radius Squared
You're given diameters, so half the values and you get the radius.
ah bugger yes, ive missed the simplest of thing, the measurment is in diameters not radius. school boy error!
Then square that, and times by Pi. e.g. (0.1 / 2) = 0.05, squared = 0.0025, times pi = 0.007854 m^2
Same for the other dimension, (0.08 / 2) = 0.04, sqaured = 0.0016, times pi = 0.0050265 m^2
Subtract the smaller value from the larger value to get the effective area = 0.0028274 m^2
yep the above is all fine makes sense
The 3m length is for the later part in the question. You don't need it for the stress. Stresses are based upon the 2D area.
ah i see thanks
Stress is given by the force applied divided by the area of the part.
yep[/color]
We know the force applied (400kN = 400,000N) and we've just worked out the area (0.0028274 m^2)
So just plug the numbers in to get the stress:
Stress = 400,000 / 0.0028274 = 141470000 Pascals = 141.47 MPa (Mega = 10^6)
yes im still following. although MPa not 100% on that part?
How's that?
top notch, i pretty much get all that. the bit im really struggling with the strain, which is below.
Edit: And for the second part:
You know the pipe length = 3m
The Young's Modulus for the material = 200,000 N/mm^2 (1 N/mm^2 = 1MPa), so you've got 200,000 MPa = 200,000 x 10^6 Pa
umm not sure im fully getting the above? could we clarify that the ^ stands for
Young's Modulus is found by, Stress divided by Strain
We have worked out stress, and we are given Young's modulus, so the only unknown part is Strain.
yep
Strain is calculated by the change in length divided by the original starting length. = ∆L / L
So we can swap the strain value in the Young's modulus equation for the ∆L/L part.
To give:
Young's Modulus = Stress / (∆L / L)
Then re-arrange to give ∆L on it's own:
Change in length = (Stress / Young's Modulus) * Original Length
So plug in the numbers:
Change in length = (141.47 x 10^6 / 200,000 x 10^6) * 3 = 2.12205 x 10^-3 m
To convert into mm times by 1000 = 2.12mm extension
Ummm yeah i think im with you
You've just got to watch out for the units, and the rest will pop into place.
Keep everything in S.I. units and you' can't go wrong.
Forces in Pascals: (Pa), Distances in Meters, m. etc...
Dan
i need to type this out check everything and make sure i 100% get it. many thanks for your help.
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anything with concrete on the other hand is civil... but since the same laws apply it can be solved with the same calculations. Have you looked at hibbelers books? We use these at school and they are very clear and easy to understand
Originally Posted by andy_con
