Youngs Modulus vs Shear Modulus

[InnDesign]

We have conducted an instron pull test on a small pin. From this, the computer gave us a graph of the test (load vs extension). From that we determined the max. load. This graph can be used to find youngs Modulus.
My question to you is, can we take this graph and make a line parallel to the line of elasticity and going through the max load point for our y-coordinate and figure out an x-coordinate. Can that x-coordinate be used in calculating shear modulus formula E=FL/(A/delta x) for delta x?

We are using E from the graph, max load for our F, Cross-sectional area of pin for A, and the legth of section of importance for L..see attachment

 

[rb1957]

isn't G = E/(2*(1+v)) ... v = .3 ... G = (5/13)*E

 

[PratsA]

The formula you posted looks more like Young's modulus (E) than shear modulus (G), in which case you can't use it like you're describing.

In my last job I performed many pull tests on LCP dogbone test specimens. I had an axial strain gauge and a transverse strain gauge, which allowed me to measure Poisson's ratio. Using the Instron's automatically calculated Young's Modulus, I had the software calculate shear modulus using the same formula that rb1957 posted. If you don't have the strain gauges you can use a decent approximation for poisson's, like rb1957 showed.

 

[InnDesign]

Thanks but i can not use this formula without an accurate poisson's ratio, I can not just assume .3

Thanks for your help though, any thoughts or comments?