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NE Iowa | I agree with your numbers that the moment of inertia between the two options are almost the same. But the max stress is equal to the bending moment times the distance from the centerline divided by the moment of inertia. So the 4" thick one will start to bend at 33% less load then the 3" thick one. As for material, 1045 is not that strong unless it is heat treated. Cold drawn bar is also much stronger than hot rolled bar. Standard low carbon bar that is stocked at steel wharehouses is 1018. 1018 cold drawn is 54,000 psi yield strength and hot rolled is only 32,000 psi. 1045 cold drawn is 77,000 psi and hot rolled is 45,000 psi. A fairly common material that you could consider would be 4140 that is prehardened. It is often called 4140 "quenched & tempered" or 4140 "pre-hard". My steel catalog says it is available in 6" x 4" and that has around 131,000 psi. | |
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Dtawbar engineering
