For type 316 Stainless; E = 28,000 kPSI
When I convert your number to metric I come up with 193KN/mm^2 which is a lot higher than the one I quoted (107.5). When I looked up E again on the web the numbers I come up with now are closer to the ones you give so I guess it is more proper to use the constant you gave. The equation for Delta L is of course the same (Phewww!! thank goodness for that)
For 7/16 wire - S = 15% * (20,000#)/(Pi * (7/32")^2) = 15% * 133,040 PSI = 19,956 PSI
I note that American's frequently use the # sign. Can you explain what it means?
Use inches or mm for the shroud length; multiply by .000736 and get the length you need to stretch the cable.
For a shroud 55' long: dL = 660" * .000736 = 0.485"
For a shroud 20' long: dL = 240" * .000736 = 0.177"
It's -fairly- independent of wire diameter; but clearly dependent on length! You could use this for type 316; (but of course the standard disclaimer applies); and it does not take into account deflection of the rig or hull when you tighten the shrouds. Again; you should use an appropriate tension gauge to determine the actual rig tension.
I can understand the apparatus needed to measure an extension of a few mm over a length of 2 m.
What would you use to measure the 0.485" (say) in the 55' shroud to ensure that you don't tension it more than 15% of breaking strength?