Poisson's Ratio Coursework: Urgent Help Needed!

AI Thread Summary
The discussion centers on a student seeking assistance with their A2 physics coursework on Poisson's ratio, specifically using aluminum foil and strain gauges to measure strain. The setup involves applying tension to the foil and measuring voltage changes with a Wheatstone Bridge circuit. Key questions include the appropriateness of the setup and clarification on whether to use one or both transverse strains when calculating Poisson's ratio. It is confirmed that Poisson's ratio is calculated using the transverse strain (in the direction perpendicular to the applied force) divided by the axial strain (in the direction of the force). The student expresses urgency for guidance to achieve a good grade for university admission.
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Poisson's Ratio coursework - Urgent help needed!

hello,

I'm currently working on a coursework for my A2 physics on Poisson's ratio
i'm finding the ratio for aluminuim using aluminuim foil and strain gauges, adding masses to a clamp on the end of the foil (so foil is under tension) and getting a change in voltage using a Wheatstone Bridge circuit.

I have 2 questions, firstly, as I have never used strain gauges before, could you let me know if my set up sounds reasonable?

also, i know that to get Poisson's ratio, i need the tranverse strain divided by axial strain, but is this the tranverse strain the change in width/strain at 90 degrees to the force, or the change in cross-sectional area/ the change in width AND depth?

Thank you for your help! I'm really worried about the coursework and i really need a good grade to get into university!

(sorry for posting twice - i wasn't sure if i was in correct section)
 
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The circuit depends on the strain gauge, but a Wheatstone bridge is common. What kind is it?

See - http://www.sensorland.com/HowPage002.html
http://www.omega.com/Literature/Transactions/volume3/strain2.html

Measuring Strain with Strain Gages
http://zone.ni.com/devzone/cda/tut/p/id/3642 (pdfs available)
http://zone.ni.com/devzone/cda/tut/p/id/7130

Poisson's ratio is the measure of strain in transverse direction (normal to force) to strain in longitudinal direction (parallel with force).

If one has a rectangular parallelpiped sample under tension, the strain will be positive in the direction of tensile force, and negative (contraction) in the two transverse dimension. Volume will be preserved (assuming temperature is constant).
 
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thank you for your reply, it was very helpful
you said that there would be contraction in the two transverse dimensions, so to get a value for poisson ratio would i have to use both of these strains divided by the positive strain in direction of force? or is only one needed?

thanks again very much for your help!
 


sorry, i forgot to mention, the strain gauge is a metallic strain gauge
 
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