Hi Daniel,

Your elastic modulus is off by an order of magnitude and there is something
terribly wrong either in the data acquisition or in your interpretation. I
don't know what is the sensitivity of your load cell. Check the smallest
load your load cell can measure and make sure your applied load is more than
that. Perhaps you can try pausing the machine after deforming to certain
length and check manually if the deformation and load data are comparable to
the expected values.

Cheers,
Prasanna



On Wed, May 27, 2009 at 3:11 AM, Daniel Park  wrote:

> Hi, all.
>
> I have questions on the Young's modulus measurements of electroplated
> nickel samples I did today. MTS machine with 150 kN load cell was used for
> tensile testing. The original 135 mm diamater nickel sample was made from
> electroplating of nickel (3.5 mm thick) at 20 mA/cm^2 in nickel sulfamate
> bath. Then the large nickel sample was machined into pieces of 100 mm long,
> dog-bone shaps based on the ASTM standard. The thickness was reduced to 3
> mm, the length of the reduced section was 32 mm, and the width of the
> reduced section was 6 mm. Those values were entered prior to the MTS tensile
> testing. I used a pulling speed of 0.5, 1, 2 mm/min and pulling was done
> until the machined piece broke in half.
>
> Then I got a data with stress (MPa) and strain (%). The perplxing thing I
> found was that the Young's modulus caculated from the slope using the MST
> software based on the measurements was just 10 GPa. With different pulling
> speed, the data remained at the close range of 10 GPa. And even when I
> checked with extracted data file, the data was similar. Interestinlgy, the
> yield strength was in the range of 700 MPa for all three samples.
>
> Does anyone know why I got this small Young's modules? Is the load cell too
> big for the measurements?
>
> Anyway I am going to buy a bulk nickel piece, have it machined into the
> same shapes, and measure the Young's modulus using the same setup again. I
> hope anyone who knows about the issue I brought up can provide some helpful
> ideas.
>
> Thanks in advance,
> Daniel

Thanks & Regards,
Prasanna Srinivasan