# Axial stress

A steel bar that is 16mm in diameter is resisting a force of 25kN. What is the normal axial stress in the bar(MPa)

Since MPa = N sqmm would it be 25kn/(0.016m x 0.016m)

Im more after the process on how to get the answer than the answer itself.

## Answers and Replies

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vela
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Start by looking up the definition of stress.

Yes i have and i get the picture in my head. But i just cant place where the 16mm goes.

vela
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What quantities goes into calculating the stress?

Perhaps you're simply missing the implication of the use of the word diameter.

F/A?

Force being 25kn and the area being 16mmx16mm?

vela
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Good. What precisely does A stand for? It's an area, but the area of what?

The cross sectional area of the beam?

vela
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Right. The cross-sectional area depends on the shape of the cross section. A=0.016m x 0.016m would work if the cross section were square, but is that the case here?

Does not specify. So than we would just do 25kn/0.016m = to give us 1562.5kNm converting this to Nmm would give us 1562 x 10^6 Nmm

am i somewhat right?

vela
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No, that's not correct. For one thing, when you divide, the units divide as well, so you end up with kN/m, not kN m.

What does the 16-mm given correspond to? The problem statement implies what the shape is.

The 16mm corresponds to the bar

vela
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The length of the bar?

yes, uniformly accross the bar

Figured it out.