Hi Gordy,

about the 1,8 kg test weight:

I've asked them and it seems to be just an arbitrary choice; maybe not that bad because this force is much lower than the breaking strength of most fly lines and seems to be still within the linear range.

I tried today a similar static test with a chinese DT8F:

Same measurement procedure as yours, but in my case, no pause between the measurements.

--

However this is still a static test and a DMA analyzer is out of reach for a hobbyist. So my idea is a simple dynamic test: measure the step response with a test weight.

I tried that with 1,6m #30 lbs running line:

* added a 500g test weight to the fly line section

* recorded the oscillations with my smart phone after I've pulled and released the test weight.

* analyzed the oscillations with the "Tracker" software (see

https://physlets.org/tracker/)

For the analysis I've entered a equation for a damped sine wave,

see

https://en.wikipedia.org/wiki/Damping
\(y(t) = A \cdot e^{-\lambda t} \cdot \cos(\omega t - \phi)\)

where

\(y(t)\) is the instantaneous amplitude at time ''t'';

\(A\) is the initial amplitude

\(\lambda\) is the decay rate

\(\phi\) is the phase angle

\(\omega\) is the angular frequency

I've slightly modified this function, because I've seen a linear offset, tuned then the parameters manually to get a match.

You can compute from the decay rate the damping ratio: \(\zeta = \lambda / \sqrt{\lambda^2 + \omega^2} \). Here the system is underdamped because \(\zeta < 0\). From the damping ratio you can then compute the damping coefficient and this can be used for a (damped) mass-spring simulation.

Torsten.