Effect of inner radius of rectangluar tubing during bending

[MOUT]

I am trying to determine how the inside radius of a rectangular tube effects the strength during a bending test.

My gut tells me that a larger inside radius would increase the strength because of the added cross sectional area (also second moment of area) and decrease of any stress concentration in the radius.

I cannot see any benefit in decreasing the radius but it has been suggested that this will increase the strength of the part. Is there any merit in this?

Any information you could give as to the pros and cons for either scenario whould be appreciated.

 

[rb1957]

sort of depends ...

if you're machining from a block (so that the IR and the OR are unrelated) then a larger IR would be better, for the points you mention.

if you're bending sheet to make the tube then i think there are a couple of factors to consider ...
1) minimum bend radius (for a given material/process) and
2) a smaller IR will have more material further from the NA (than a larger radius) and so it'd be better

 

[MOUT]

In this case the IR and OR are unrelated...thanks!