# Stress anaylsis inquiry

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1. Mar 6, 2015

### Amr719

1. The problem statement, all variables and given/known data
For reasons based on cost,weight,availability , etc., the choice is made to construct the rod from aluminum of
σall = 100 MPA. What is an appropriate choice for the rod diameter ? Givens: (P=50 KN)
2. Relevant equations

3. The attempt at a solution
σall=P/A , then he get the Area and from area he then gets the Diameter=25.2mm

Then he said an aluminum rod 26m or more in diameter is adequate
My question is : why an aluminum rod of 26m or more in diameter is adequate ?!!

2. Mar 6, 2015

### PhanthomJay

25.2 mm diameter required, use 26 mm, not 26 m

3. Mar 6, 2015

### Amr719

I meant 26mm , I don't know why 26mm or more . Why not less and why more ?

4. Mar 6, 2015

### PhanthomJay

If 25.2 mm diameter is required, then if you use a lesser diameter, you will exceed the allowable stress. So you have to round up to the next available greater diameter. I am not familiar with metric diameters available for aluminum rod, if 26 mm dia not available, you'll have to go to say 30 mm diameter, or whatever is in stock that is in that range.

5. Mar 6, 2015

### Amr719

Great .Thank you very much !!