Slide 6
Since the test machine
is not infinitely stiff, your measured rotation includes the rotation
of both the sample and of the test system. To account for this we
can model the sample and test system as springs in series, so that
the total system stiffness is given by one over k total equals one
over k sample plus one over k test machine. To determine the stiffness
of the test sample rearrange the equation so that one over k sample
equals 1 over k total minus 1 over k machine. In a separate experiment
we have measured the stiffness of the testing machine to be 42,800
Nm/radian.
