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  • sUche2tu commented on Captain Robert's instructable Bend Metal Without Expensive Tools3 years ago
    Bend Metal Without Expensive Tools

    Structural engineer here. What you're talking about in Step One is NOT "determining the yield strength of the metal." Rather, you are determining the STIFFNESS of the tube section."Yield strength" is a property of the steel, the stress at which the steel will begin to deform plasticly - that is, it won't spring back into shape when you remove the force. It's a material property unrelated to the geometry of the steel piece you're looking at.What you're doing in this step is seeing how much deflection results from a given force - in this case from your arm. When you remove the force, the steel tube resumes its original shape because you're still in the elastic region. However, when you bend the tube to form the curve you're talking about in the rest of the article, you...

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    Structural engineer here. What you're talking about in Step One is NOT "determining the yield strength of the metal." Rather, you are determining the STIFFNESS of the tube section."Yield strength" is a property of the steel, the stress at which the steel will begin to deform plasticly - that is, it won't spring back into shape when you remove the force. It's a material property unrelated to the geometry of the steel piece you're looking at.What you're doing in this step is seeing how much deflection results from a given force - in this case from your arm. When you remove the force, the steel tube resumes its original shape because you're still in the elastic region. However, when you bend the tube to form the curve you're talking about in the rest of the article, you've gone into the plastic region where the steel won't spring back straight. There's no way you will come close to that level of force using your arm unless the tube is very thin or very small diameter.The determining factors for the deflection you're inducing in your "test" are 1) the diameter of the tube and 2) the thickness of the tube. If you know those for a given piece of steel tube, you can calculate pretty accurately what the deflection's going to be without ever touching it,And if you know the specification of the steel, you can also determine the yield point by calculation.

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