Poisson's Ratio Coursework: Urgent Help Needed!

[lottie44442]

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)

 

[Astronuc]

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).

 

[lottie44442]

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!

 

[lottie44442]

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