|MadSci Network: Engineering|
Dare, Your question is a good one and it very much misunderstood. Oddly enough, I cannot locate any information to explain the bending mechanics specific to hollow and solid bodies. So, we need to apply the rules of mechanics to understand the mechanical forces involved. To directly answer your question, we need to visualize a 2" round solid steel bar and a 2" O.D. steel tube both clamped to a support on one end. For this example, both members are 4’ long and we will use a 1/32" wall for the 2" tube. Now suspend a 1 lb. weight on the unsupported ends of each member. Chances are neither member will bend much at all. Lets start to increase the weights in 10 lb. increments. As the weight increases the solid bar will start to bend before the tube because the top surface of the tube is in tension and the bottom surface is in compression, thus opposing stresses. The stresses are the same for the solid bar however the stresses are spread out over much more material so the solid bar will deflect more than the tube at the lower weight range. Increase the weight to 500 lb. and the solid bar will bend more but guess what! I would not want to be standing beneath the tube under this amount of weight. As the weight increases, the tube will start to bend but since there is less material, it will reach its ultimate yield strength, progress into the region of plastic deformation and finally catastrophically fail much sooner than the solid bar. In final analysis, the resistance to bending prior to failure depends upon the mass of the member and the weight applied. Please note the example above is just that, a paper example. The dimensions and weights are theoretical and must be proven. However the concept is correct. If it were not, we would be out there drilling a lot of holes through a lot of construction members. I hope this gives you better insight on the workings of solid and hollow bodies. If you decide to conduct an experiment, I would appreciate you letting me know the results. Thank You.
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