Why is a 26 mm diameter adequate for a 50 kN aluminum rod?

[Amr719]

Homework Statement

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)

Homework Equations

The Attempt at a Solution

σall=P/A , then he get the Area and from area he then gets the Diameter=25.2mm[/B]
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 ?!

 

[PhanthomJay]

Homework Statement

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)

Homework Equations

The Attempt at a Solution

σall=P/A , then he get the Area and from area he then gets the Diameter=25.2mm[/B]
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 ?!

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

 

[Amr719]

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

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

 

[PhanthomJay]

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

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.

 

[Amr719]

Great .Thank you very much !