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Strength of solid versus hollow axles
Recently therehave been a few posts which may confuse (or indeed
originate from) uneducated reader(s) concerning the strength of solid versus hollow axles. The strength of any particular cross-sectional shape can be described by quantity called the section modulus, which is kind of a combination of the amount of material and the distance away from the bending line - usually taken as the centre - of the section. If we take a typical rear axle the OD is pretty close to 0.4 inch. A hollow axle has an ID of pretty close to 0.2 inch - giving a tube or column with a wall thickness of almost 0.1 inch. Using these numbers: The solid axle will have a section modulus of 0.00627. The hollow axle will have a section modulus of 0.00588 For front axles, which are around 0.35 OD, the numbers a Solid - 0.00435 Hollow - 0.00390 Now, of course, these figures mean that a solid axle is stronger. There are other factors which affect the strength of axles, of course; the choice of material, the heat treatment, the surface finish, etcetera. A particular effect which cannot be eliminated from hollow axles is that of the roughness of the inside surface of the hole. Solid axles, of course, do not have this, and so also do not suffer from the chance that a crack may start at an irregularity on the inner surface. Cycle axles of the highest prices (and, the buyer may sometimes presume, the highest quality) are finished very well on the outside surface; but the inside is a hidden quantity, difficult to finish and inspect. In the real world of cycling, there are axles made from different material and to different qualities. Of course it is possible to find a particular hollow axle which may be stronger than another particular solid axle - but to claim in abstract that a hollow axle is stronger (or even no weaker than) than a solid one is clearly wrong. |
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Strength of solid versus hollow axles
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Strength of solid versus hollow axles
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Strength of solid versus hollow axles
I've had 2 solid axles break (both back wheel), but no hollow ones.
cheers Jacob |
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Strength of solid versus hollow axles
On Sun, 24 Sep 2006 14:03:29 GMT, Bob Johnstone
wrote: wrote: The strength of any particular cross-sectional shape can be described by quantity called the section modulus, which is kind of a combination of the amount of material and the distance away from the bending line - usually taken as the centre - of the section. The section modulus doesn't actually describe the strength of a beam. It describes the stiffness. There are other factors which affect the strength of axles, of course; the choice of material, the heat treatment, the surface finish, etcetera. Another important factor is whether the axle is being compressed by a quick-release skewer. I would expect the compression from the skewer to increase the strength of an axle in a way similar way to pre-stressed concrete. The skewer may also provide a back-up if the axle fractures. Well, it doesn't. Compression of a long slender colum subject to bending forces increases the likelyhood of bending and failure. Concrete is not steel; nor is it (usually) hollow. |
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Strength of solid versus hollow axles
On 24 Sep 2006 10:51:09 -0700, "normanwisdom"
wrote: I've had 2 solid axles break (both back wheel), but no hollow ones. It's not because they were solid as opposed to hollow, but because they were either of lower quality steel, poorer finish, or subject to loads that the hollow ones weren't. All else being equal, solid is stronger. "All else" includes not having one made of "foam rubber". |
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Strength of solid versus hollow axles
wrote in message ... Recently therehave been a few posts which may confuse (or indeed originate from) uneducated reader(s) concerning the strength of solid versus hollow axles. The strength of any particular cross-sectional shape can be described by quantity called the section modulus, which is kind of a combination of the amount of material and the distance away from the bending line - usually taken as the centre - of the section. If we take a typical rear axle the OD is pretty close to 0.4 inch. A hollow axle has an ID of pretty close to 0.2 inch - giving a tube or column with a wall thickness of almost 0.1 inch. Using these numbers: The solid axle will have a section modulus of 0.00627. The hollow axle will have a section modulus of 0.00588 For front axles, which are around 0.35 OD, the numbers a Solid - 0.00435 Hollow - 0.00390 ........Snip ........................ To add my twopenneth to this topic. The reason why a hollow bar or beam will be close in stiffness to a solid one is due to the fact that, in bending, the stress will be concentrated at the top and bottom of the beam. If you bend a measuring ruler so that the middle is higher than the ends, the top part will be in tension and the lower will be in compression. Assuming that the upper half of the cross-section mirrors the lower half then halfway up the cross-section will be a neutral axis where no stress occurs. If the cross-section is irregular then the neutral axis moves according to the concentration of material. Using this principle we can see that in the centre of a solid axle, there is hardly any stress in bending therefore it makes sense to concentrate the material at the outer edges where the greatest stress occurs, it also saves a lot of weight. This is why I-beams used in construction are shaped as they are, the material is used more efficiently. The clamping of the QR lever onto the axle induces axial compressive stress and does not gain strength in the way that pre-stressed concrete does. Concrete is weak in tension but strong in compression therefore pre-stressing induces compression at the top and bottom of the beam prior to loading. Placing a load onto a pre-stressed beam creates a tensile stress underneath which is balanced by the compressive stress already introduced into the beam. Hope this clarifies the matter, AT |
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Strength of solid versus hollow axles
All else being equal, solid is stronger.
Remember something about mutually beneficial relationships between a fungus-type-thing and oak trees. The fungus-type-thing would eat the inside of the oak tree, and the oak tree benefited from being hollow, and thus being able to withstand higher winds that would otherwise knock 'em down. I'm not sure this helps much, as hollow oak trees probably aren't ideal for making axles thobut. Mark. |
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Strength of solid versus hollow axles
On 26 Sep 2006 11:10:27 GMT, Mark Thompson
pleasegivegenerously@warmmail*_turn_up_the_heat_t o_reply*.com wrote: All else being equal, solid is stronger. Remember something about mutually beneficial relationships between a fungus-type-thing and oak trees. The fungus-type-thing would eat the inside of the oak tree, and the oak tree benefited from being hollow, and thus being able to withstand higher winds that would otherwise knock 'em down. The tree would bend more, and reduce the stress on the roots. This example does not apply to cycle axles because a) the trunk of the tree was not breaking b) cycle axles don't have roots. I'm not sure this helps much, as hollow oak trees probably aren't ideal for making axles thobut. Neither is foam rubber. |
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