determining torsional yield with dasylab

[dsperfslage]

Hello all,

I am trying to calculate a 0 degree torsional yield point using dasylab.  Right now I am plotting my torque vs deflection, but need help determining the yield of the metal.  

I was thinking about using some kind of piece-wise slope comparison to do this, but can't find anything on it.  Any ideas?

[CJ_Butler__DASYLab_Pro]

I'm not familiar with the math that you might need to do these computations... do you have some more information, or a link to an explanation?

[TomRizzo]

Hello,

How do you measure extension?

And CJ is right, we need more information on the setup and channels used.

[dsperfslage]

Hi,

Example, Ch 1 is torque & Ch 2 is angle.  Ch 1&2 are plotted against each other.  As the object is twisted the angle of rotation increases and torque is increase proportionally.    This creates a "spring rate" of the object.  Eventually, the torqe becomes too great and it yields the object.

I've included a chart as refference.

As you can see, the slope of the line is fairly constant and then it yields.  This causes a change in the slope. It is at that point I need to know automatically.

Thanks for the interest in helping!

Dan

[TomRizzo]

Ahhhh,

Now I got it.

What you need to do is to calculate the realtime slope and then use a PrePost trigger.  In the limits you enter the min max values that you would like to have the system within.  As soon as the slpope will go outside those values, you will trigger a high value on the output of this module.

[dsperfslage]

Hi Tom,

 Thanks for the reply.  I haven't figured out a way to calculate real time slope, any examples to do such a thing? 

 The objects are different everytime, but if I know the real time slope value I might be able to take that value after a peroid of time and compar to it as the test is in process.   Interesting.

  Let me know if you have any examples of that real time slope idea!

Thanks,
Dan

[CJ_Butler__DASYLab_Pro]

Slope is usually easy... just use the Differential/Integral module in the Mathematics group. It simply computes delta-y / delta-x, where delta-x is the sample distance in seconds.This doesn't help with the X/Y comparison however.

You can also use the Arithmetic module to compute a running difference for each channel (Arithmetic/One Channel), and then use a second Arithmetic (two channels) to divide. That will get your slope.