Solving Cable Tension Question with Proportion

[jw2007]

I have a locking device with a cable running through it (think of pieces of PVC pipe with a cable through them). I apply pressure and pull on one end of the cable tightening it and pulling the pieces together so I can lock it with a cam device. To lock it presently it requires 1200 psi (hydraulic pressure) applied to the cable (tension). There is a spacer block .994" long that I pull the cam lock past to get to 1200 psi. I need to increase the locking tension to between 1250 psi and 1400 psi. I need to determine the length of the new spacer. I intend to calculate this as a proportion since the cable, which is steel, I believe should have a constant spring coefficient. My calculation for my next move is as follows:

I plan to add a spacer that is an additional .085" in length making the overall spacer length 1.079"

.994"/1200 psi = 1.079"/X psi

X = 1.079"(1200 psi/.994")

X= 1302.615 psi

Does this make sense?

 

[FredGarvin]

Assuming that everything is linear this makes sense. If we were talking about a rigid bar then since it is a low stress, you should definitely be in the linear range. I think you should end up close enough to what you want.

 

[Chronos]

The stress is negligible compared to the yield strength of steel. A linear approximation is appropriate.