Interference fit analysis question.

[bobito5]

I am looking for any online text concerning stress analysis for interference fit situations, i.e. thermal fit cylinders. As an aside; is anyone familiar with the "Engineering Solid Mechanics" book by Ragab and Bayoumi. It is littered with typos and errors and is frankly totally unsable, I am totally disappointed in it.

 

[Andries]

Hi,

I don't know about online info on interference fit analysis but all good strength of materials books should have what you look for.
Try Strength of Materials by Egor Popov of UCLA - I think it is still in print. It is a very good text and also treats interference fit problems.

Regards

Andries

 

[bobito5]

I have one further question. I've been looking through number of texts with reference to interference fits, i.e. compound cylinders, and have a recurring issue. Most approaches use an interference fit pressure and common radius. The reality is that I only know what the dimensions of the two mating parts are before assembly, how am I supposed to know what the final mating radius is? Is there a common method to determine this or am I just missing something?

 

[rguil]

I would treat the problem with the assumption that the outer component will not yield.

 

This is a so called statically indeterminate problem. If the cylinders are thin wall same material then it is safe to assume that the displacement is equally divided among the two, so split the difference and use the circumferential strain to get at the stress.

If one is very thick then assume that it does not stretch and that the thin walled tube takes all the stress. Caution is required if the outer is cast iron and thin. Theraduius ratio can be found by relating the circumferential stiffness. So, outer 2X so stiff strain is 1/2 of total.

 

As Martin pointed out, this is a statically indeterminate problem. Assuming linear elasticity, a simple method for solving this problem is contained in "Advanced Mechanics of Materials", 5th ed, Boresi, Schmidt, Sidebottom, Chap 11.

Given the initial dimensions and material properties, you know the stiffness of the cylinders and the total displacement at the interface .... i.e. the sum of the contraction of inner cylinder plus expansion of outer cylinder. The distribution of displacement depends on the relative stiffness of each cylinder. The method contained in the reference above uses the displacement equations for a thick cylinder subject to internal/external pressure to find the pressure required to force the sum of the radial displacements at the interface to equal the interference. This requires some iteration that can be handled fairly easily by using the solver feature in MS Excel, or by using any one of a number of methods in Mathcad.

 

[metman]

bobito

Machinery handbook has a good section on shrinkage fits but only deals with cast iron vs steel or steel vs steel with tables of factors to be used in the equation. the tables allow for solid or tubular shaft. Jesus is the WAY

 

[bobito5]

visito2002,

that was exactly the answer I was looking for. Thank you that was very helpful.

bobito

 

bobito,

you're welcome