# Coaxial bars

1. May 7, 2005

### chandran

i have attached a doc file. it shows two coaxial circular bars of different material and a force(30kn) is applied in the top. I think the internal forces in both the bars
will be 30kn. Am i correct.

bar1 is made of steel and bar 2 of aluminium. the total length of the structure is
10metres.

2. May 8, 2005

### quasar987

No .doc file attached.

3. May 8, 2005

### chandran

i have attached a jpg since memory was less.

File size:
3.5 KB
Views:
43
4. May 9, 2005

### FredGarvin

I can't really make out the picture. I can't tell if the load is applied to both parts or the inner one. If you are asking what the compressive load is and the 30kN is applied to both bars, then you are correct.

As another possibility, you may also nee to look at this is with the application of the load to the inner shaft, which will compress according $$\Delta = \frac{PL}{AE}$$ Since the volume remains constant that should give you an ability to calculate the new diameter of the shaft. The same holds true for the outer shaft, simply using the constants for a different material. Once you have calculated the new diameters, chances are that there is an interference between the two. That interference will produce a contact pressure and thus an internal stress between the two.