Determining preload torque needed on screw based on pressure in PSI

[Jordan23]

I am currently running a calculation for a research project that I am working on. We are determining pressure that we are seeing in a chamber by using copper cans. I have an expected pressure that I want to run the calculation with, which is what I want to base the preload on the copper can on. We will be using a fine-thread alloy steel socket head screw, M20x1.5mm thread, 50mm long screw with the end touching the copper can to preload onto the copper can. If anyone has comments on what calculations need to be run in order to get as accurate as possible on the torque needed to preload a pressure in psi, it would be greatly appreciated. I have done the easy calculation of just doing surface area of the screw head times psi and then estimated the lever arm length, but this is definitely not close to what is truly needed.

 

[GregLocock]

Please post a diagram of what you are doing.

 

[waross]

Best bet; Apply a known pressure to the can and then cancel it out by loading the screw jack.
Varying and possibly unknown friction and sticktion in the screw may render your actual preload wildly inaccurate.
If your copper is supported by the edges and pre-loaded in the center, the effective area may be difficult to determine.
Also, pre-load implies that the screw jack is loaded before the pressure to be tested is applied.

We are determining pressure that we are seeing in a chamber by using copper cans.

We need some explanation as to how this is being done.
What pressure range are you looking at?
Peak transient or steady state pressure.
What is generating the pressure?
Is your basic research to generate a pressure or to measure the pressure generated?
From what you have told us so far I am reminded of a mis-quote sometimes attributed to Thomas Alva Edison;
"I have not failed 1000 times. Rather I have determined 1000 methods that will not work."

 

[Jordan23]

I am working on a basic diagram now. Basically, the copper is a small cylinder with one flat face sitting against a "piston" and the other touching the tip of the screw (note the surface area of the cylinder is much smaller than both the surface area of the screw tip and the piston). The sides of the cylinder are not confined. The screw is torqued to put a preload pressure on the copper cylinder (in the range of 50,000 to 100,000 psi). The piston is not able to slip out the opposite end. The assembly is set into a casing and mounted against a wall with the face of the piston facing out. The shock pressure will then be created that will hit the piston and crush the copper against the tip of the screw.

 

[waross]

Example:
Mechanical advantage of a screw;
Applied force = 1 ft-lb.
Distance the force is applied; 3.414 x 12 in = 37.7 in.
Distance screw advances per turn = 1/16 in.
MA = 37.7 in : 1/16 in = 603:1