Finding strains and stresses on a hydraulic cylinder - NO external pressure?

In summary, the conversation discusses running a test simulation on a Festo rig with a hydraulic cylinder, using an internal pressure of 60Bar and a strain gauge. The speaker suspects the setup to be faulty and considers using Lane's equation, but is unsure if an external pressure is needed. They also mention a thick walled cylindrical pressure vessel and reference resources for equations.
  • #1
jrhickin
3
0
I'm running a test simulation on a Festo rig, with a hydraulic cylinder measuring 45mm internal diameter and 54mm external diameter. The testing requires an internal pressure of 60Bar with no external pressure applied. The strain gauge and setup I'm running it on I suspect to be faulty, and I can't get any sensible principle stresses and strain answers out of it. Is there any way of working it out by hand? I want to see if it's the gauge that's at fault, the system, or if it just happens to be a strange figure.
Thinking back to my lectures, I recall Lane's equation, but as far as I know you need an external pressure to make that work. Is this the one to use? I haven't done it in ages, so any hints on how to work it out would be useful.
 
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  • #2
This is just a thick walled cylindrical pressure vessel isn't it?
 
  • #3
Yes, it is. It's standard steel, 200GPa for the Young's modulus if that's any help!
 
  • #4
You don't need an external pressure to make the Lame equations work.
 
  • #5
Then just use thick walled pressure vessel equations to find the stresses and strains.
 
  • #6
You don't? I thought that was what a or b was in it?
The equation I have for Lame is a + b/r^2. How do you work it out? It's been a long while since I've had to use it, mind!
 
  • #7
Check out engineering tool box (google it), they'll have the equtions.

They are also in Shigley - Mechanical Engineering Design if you have that book.
 
  • #8
You should know the boundary conditions. External pressure = 0 and internal pressure = 60bar.
 

1. What is the purpose of finding strains and stresses on a hydraulic cylinder without external pressure?

The purpose of this task is to determine the potential mechanical failures or weaknesses in the hydraulic cylinder, even when it is not under any external pressure. This can help prevent accidents and ensure the safe operation of the cylinder.

2. How do you find strains and stresses on a hydraulic cylinder without external pressure?

The most common method is through strain gauge measurements. This involves attaching small sensors called strain gauges to the surface of the cylinder and measuring the changes in electrical resistance as the cylinder is subjected to different loads. These measurements can then be used to calculate the strains and stresses on the cylinder.

3. What factors can affect the strains and stresses on a hydraulic cylinder?

There are several factors that can affect the strains and stresses on a hydraulic cylinder, such as the internal pressure of the fluid, the material and thickness of the cylinder, and the geometry of the cylinder. Other external factors, such as temperature changes and vibration, can also have an impact.

4. Why is it important to consider strains and stresses on a hydraulic cylinder?

Strains and stresses can cause wear and tear on the cylinder, leading to potential failures or leaks. By identifying and monitoring these strains and stresses, maintenance and repairs can be performed before any major issues occur, ensuring the safe and efficient operation of the hydraulic system.

5. How often should strains and stresses on a hydraulic cylinder be checked?

This can vary depending on the specific application and operating conditions, but it is generally recommended to check strains and stresses on a regular basis, such as during routine maintenance or after any significant changes in operating conditions. It is also important to monitor and record strains and stresses over time to identify any trends or potential issues.

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