Hydraulic tensioner pressure conversion in a fretting testing rig

[fabfour]

Hello all

I have a problem I hoped some of you guys might be able to shed some light on.

First off, I have a rig like crudely drawn in the attachment. In it is a block clamped between the two plates using 4 bolts that go through the rig. The bolts have nuts on the left side and hyrdaulic tensioners on the right side.

The block has jagged edges that are in contact with the plates, the area of these jagged edges are 1290.3 mm^2 on each side, so both sides add up to 2580.6 mm^2, or 2.5806*10^-3 m^2

The smallest cross-sectional area of the bolts are 364 mm^2

The area of the hydraulic tensioners (as inscribed on them) is 20.27 cm^2, or 2.027*10^-3 m^2

I am required to excert a compression force of 15 000 psi on this block using the hydraulic tensioners. This means I have to find the pressure input needed in the hydraulic tensioners.

What I did was as follows:

15 000 psi = 103 421 359 Pa

I decided to take this pressure and multiply it with the area to be clamped to get the total compressive force needed:
since 1 Pa = 1 N/m^2 => 103 421 359 N/m^2 * 2.5806*10^-3 m^2 = 266893.3 N

Since there are 4 bolts, I then divided this force by 4 to get 66723.33 N as the compressional force needed to be done by each bolt.

I then took this force and divided by the area of the tensioner to get the pressure force needed to be excerted by the tensioner in order to get the required compressional force in the bolt.

66723.33 N / (2.027*10^-3 m^2) = 32.92 MPa per tensioner.

Now, apparently this is wrong, can anyone tell me where I went wrong in this?
I don't know if this counts as student posting or not, if it does, I am sorry. But I am really lost here, and none of my mates can offer any advice on this topic.

Thanks in advance

 

[vpl]

Is it a homework assignment or school project?

If so, what have you done to try and figure out what went wrong? Did you talk to your teacher, or a grad student? Go back and read your text book? Ask other students in your class? Your questions should be focused on "Where can I find out more about this?" rather than "What did I do wrong?"

The aim of an engineering school education is to teach you how to solve the problems you will encounter when you graduate and get an engineering job. Solving the problems yourself means that you have "more tools in your toolbox" than just posting a question on an internet site and hoping someone will solve it for you.

Not saying you might not get an anwer here, but I'd suggest you post again outlining what steps you've taken to figure out for yourself where you went wrong.

Patricia Lougheed

******

Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.

 

[MintJulep]

It's generally a good idea to start by drawing a Free Body Diagram.

It's also generally a good idea to correctly state the problem.

I am required to excert a compression force of 15 000 psi on this block using the hydraulic tensioners

psi is not a unit of force.

 

[fabfour]

thank you for your input, I'll go back to the drawing board and figure it out eventually.

Best regards
KS