Force applied to objects pressed together

In summary, the von Mises stress is a stress that is applied to a material when it is in a press fit. The stress is caused by the pressure between the mating parts. You can find the basic strength of the press fit by multiplying the von Mises stress by the radius of the fit.
  • #1
mkpn24
3
0
Hello all new to the forums but I have a question. I need to find out the force that holds two pressed objects together. For example I have a piece with a diameter of 1.000 in and another piece (the shaft) with has a diameter of 1.001. The shaft is inserted .25in into the 1.000in opening. The open diameter is heated up while the shaft is frozen and then the shaft is inserted into the opening. I need to pretty much figure out how to find how much force the shaft can take before it starts to spin in the other pieces open diameter.

Im assuming there is friction force and the force of the two objects pressed together I just can't seem to figure out how to go about finding these forces.
 
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  • #2
You would be able to find the friction force of a block on a surface, yes, no?

For a press fit the parts are pressing against each other causing a stress, pressure, force.
You need to find the force between the mating parts. Multiply that by the radius of the fit and you have the torque before failure.

For the material(s) have you the modulus of elasticity and Poison ratio?

How much knowledge do you have about all this?
 
  • #3
Yes I do have knowledge about this I'm actually in a strength of materials course right now but for some reason I just can not wrap my head around this problem. It's not for school this isn't a homework problem or anything it's for an internship I have right now.

The material is 52100 steel.

E=30,000,000psi
Poisson's ration = .30

I'm thinking maybe I could find the strain but I'm not sure about the deformation of the objects would it be .0001in, which the difference in the two diameters, Over the smaller open diameter 1in?
 
  • #4
This site may help you out, from the point of view of a thick walled cylinder being pressurized.
http://www.faculty.fairfield.edu/wdornfeld/ME311/PressCylinderHam.pdf
which gives a good indication of first principles.
And from which, by the equations you can obtain the basic strength of the fit.
That should get you started.

Here are some more equations of interest, but which are more daunting, but which you may need.
http://www.engineersedge.com/calculators/machine-design/press-fit/press-fit-equations.htm

And a brief explanation of the design criteria of the von Mises stress, from where else but,
https://www.physicsforums.com/showthread.php?t=20685
 
  • #5
Can someone review this work and tell me if I'm correct please.
 

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1. What is force applied to objects pressed together?

Force applied to objects pressed together is a physical quantity that describes the push or pull between two objects in contact with each other. It is a vector quantity, meaning it has both magnitude and direction.

2. How is force applied to objects pressed together calculated?

The force applied to objects pressed together is calculated using the formula F = μN, where F is the applied force, μ is the coefficient of friction, and N is the normal force. The coefficient of friction is a measure of how much resistance there is between two objects in contact, and the normal force is the force that is perpendicular to the surface of contact.

3. What factors affect the force applied to objects pressed together?

The force applied to objects pressed together is affected by the coefficient of friction between the two objects, the normal force, and the surface area of contact. The roughness of the surface and the presence of lubricants can also affect the force applied.

4. How does the force applied to objects pressed together affect the motion of the objects?

The force applied to objects pressed together can either cause the objects to move or prevent them from moving. If the applied force is greater than the frictional force between the objects, the objects will move. If the applied force is less than the frictional force, the objects will remain stationary.

5. What are some real-life applications of force applied to objects pressed together?

Force applied to objects pressed together is present in many everyday situations, such as when walking on a rough surface, pushing a heavy object, or using tools to tighten or loosen screws. It is also important in engineering and construction, as it determines the stability and strength of structures.

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