#11
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Wheel deflection
On Tue, 28 Oct 2008 12:50:22 -0700 (PDT), Chalo
wrote: jim beam wrote: Jobst Brandt wrote: Time of loading has no effect on metals untrue. *many materials react differently depending on loading rate. *for example, this is why you have nail guns - they succeed at a high rate on driving nails into concrete whereas trying to do the same job at a lower rate always fails. * Concrete is the issue. Whack a nail into wood, or push it in with an arbor press, and it's about the same (although the whacked nail might hold better due to local heating of the wood resins). [snip] Dear Chalo, Usually I follow you because your posts are clear to even the meanest intelligence. But this is a concrete example (sorry, couldn't resist it) of how even you can overestimate the dregs of your readership. Can you explain concrete versus wood a little more from the nail gun's point of view? Cheers, Carl Fogel |
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#12
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Wheel deflection
Frank Krygowski wrote:
Does anybody know if a rim would react differently to a sudden load versus a gradual load? Â*What I mean is if you were to apply a gradual load on a wheel would that rim be able to handle a higher load before permanantly deforming than if you were to apply the same load very quickly? With suddenly applied loads, there's an inertia effect that generally makes things worse. Let's not leave it at such a vague description. Â*The question is load, regardless of its origin, inertial or dead weight. Â*The rate of stress application has no effect on metals, at least up to acoustic frequencies. That depends on exactly what Steve meant by "load." A load is a load is a load. A mass can be a load statically and dynamically but that is a load. Confusing inertial loads with stress confuses the issue at hand. Steve's question has a semantic problem. Does load mean force or mass in his question? The classic example is gently placing a load on a spring, vs. suddenly releasing the same load onto the same spring. Â*Even if the load is (barely) touching the spring just before it's released, the spring momentarily deflects twice as far as with the gently placed load, and the peak force on the spring is twice as great. Oops! What do you mean by load? Getting force mass and load scrambled does not lead to a clarification of the matter. Those are two different loads. Â*The question was about load application and possibly duration causing plastic deformation. If Steve could tell us more about exactly what he means, we could determine whether the sudden application of an object onto a spring is properly analogous. I believe it's likely, but he's given no details. I don't think your adoption of his terms helps either. If the load were applied by a mechanism that didn't involve mass and inertia, I don't believe that effect would be present. Â*But bike wheel loads do involve mass and inertia. Bicycle wheels do not involve mass AND inertia. Â*Loads are mainly rider and bicycle mass and their inertia. Â*The mass of the wheel and tire is insignificant in that respect. Â*An example of that would be to toss a wheel, with inflated tire, into the air and watch it bounce undamaged on pavement. Â*To damage a wheel in that manner would take a hefty toss, especially with a fat (2+ tire) inch. Bicycle wheels support mass. That mass has inertia. It makes a difference. You said "But bike wheel loads do involve mass and inertia." which is a jumble of misstatement. You may have meant that bicycle wheels bear inertial loads of the bicycle but they themselves have insignificant inertial effects on their own stress and deformation. Example: A 200 pound bike+rider sitting still on level ground causes certain stresses in the various wheel components. That same bike +rider dropping one foot down onto level ground causes much more stress. If Steve was envisioning anything similar, the fact that wheel masses are low has no bearing. There you go again mixing the bike+rider with wheel inertial effects. That is not an example of "But bike wheel loads do involve mass and inertia." You must mean "Bicycle loads involve inertia." Tossing the word wheel in there doesn't clarify what is meant. So, Steve, what do you have in mind? So, Frank, what do you have in mind? Jobst Brandt |
#13
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Wheel deflection
On Oct 28, 1:58*pm, wrote:
Frank Krygowski wrote: [content-free definitional posturing] [more content-free definitional posturing] I wonder why is is that an insistence on rigid adherence to (arbitrarily decided and often inconsistent) terminology so often correlates with the same person's complete failure to communicate, whether in the role of producer or receiver of information. The typical failure insists that accurate diction is essential to accurate communication; yet when the process of communication has progressed so that any outside observer can see what information is in play, the failure goes on long after the fact to insist that words be used *his* way -- though by any measure the communication of information is long complete. One is forced to conclude from the fact of his actions, in contradiction to his stated beliefs, the failure has no pragmatic interest in the transmission of accurate information. -pm |
#14
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Wheel deflection
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#16
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Wheel deflection
On Tue, 28 Oct 2008 14:27:02 -0700, pm wrote:
On Oct 28, 1:58Â*pm, wrote: Frank Krygowski wrote: [content-free definitional posturing] [more content-free definitional posturing] I wonder why is is that an insistence on rigid adherence to (arbitrarily decided and often inconsistent) terminology so often correlates with the same person's complete failure to communicate, whether in the role of producer or receiver of information. The typical failure insists that accurate diction is essential to accurate communication; yet when the process of communication has progressed so that any outside observer can see what information is in play, the failure goes on long after the fact to insist that words be used *his* way -- though by any measure the communication of information is long complete. One is forced to conclude from the fact of his actions, in contradiction to his stated beliefs, the failure has no pragmatic interest in the transmission of accurate information. -pm potm! |
#17
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Wheel deflection
On Tue, 28 Oct 2008 20:58:32 +0000, jobst.brandt wrote:
Frank Krygowski wrote: Does anybody know if a rim would react differently to a sudden load versus a gradual load? Â*What I mean is if you were to apply a gradual load on a wheel would that rim be able to handle a higher load before permanantly deforming than if you were to apply the same load very quickly? With suddenly applied loads, there's an inertia effect that generally makes things worse. Let's not leave it at such a vague description. Â*The question is load, regardless of its origin, inertial or dead weight. Â*The rate of stress application has no effect on metals, at least up to acoustic frequencies. That depends on exactly what Steve meant by "load." A load is a load is a load. with the jobstian exception of course being when that load is connected to a rubber tire, in which case it mysteriously disappears. unless you're prepared to admit time and thus rates into your simplistic little purview, in which case load is not load, etc. A mass can be a load statically and dynamically but that is a load. Confusing inertial loads with stress confuses the issue at hand. Steve's question has a semantic problem. Does load mean force or mass in his question? given your obvious confusion, would it make a difference to you? The classic example is gently placing a load on a spring, vs. suddenly releasing the same load onto the same spring. Â*Even if the load is (barely) touching the spring just before it's released, the spring momentarily deflects twice as far as with the gently placed load, and the peak force on the spring is twice as great. Oops! What do you mean by load? Getting force mass and load scrambled does not lead to a clarification of the matter. Those are two different loads. Â*The question was about load application and possibly duration causing plastic deformation. If Steve could tell us more about exactly what he means, we could determine whether the sudden application of an object onto a spring is properly analogous. I believe it's likely, but he's given no details. I don't think your adoption of his terms helps either. If the load were applied by a mechanism that didn't involve mass and inertia, I don't believe that effect would be present. Â*But bike wheel loads do involve mass and inertia. Bicycle wheels do not involve mass AND inertia. Â*Loads are mainly rider and bicycle mass and their inertia. Â*The mass of the wheel and tire is insignificant in that respect. Â*An example of that would be to toss a wheel, with inflated tire, into the air and watch it bounce undamaged on pavement. Â*To damage a wheel in that manner would take a hefty toss, especially with a fat (2+ tire) inch. Bicycle wheels support mass. That mass has inertia. It makes a difference. You said "But bike wheel loads do involve mass and inertia." which is a jumble of misstatement. You may have meant that bicycle wheels bear inertial loads of the bicycle but they themselves have insignificant inertial effects on their own stress and deformation. Example: A 200 pound bike+rider sitting still on level ground causes certain stresses in the various wheel components. That same bike +rider dropping one foot down onto level ground causes much more stress. If Steve was envisioning anything similar, the fact that wheel masses are low has no bearing. There you go again mixing the bike+rider with wheel inertial effects. That is not an example of "But bike wheel loads do involve mass and inertia." You must mean "Bicycle loads involve inertia." Tossing the word wheel in there doesn't clarify what is meant. So, Steve, what do you have in mind? So, Frank, what do you have in mind? Jobst Brandt |
#18
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Wheel deflection
Carl Fogel wrote:
Chalo wrote: jim beam wrote: Jobst Brandt wrote: Time of loading has no effect on metals untrue. *many materials react differently depending on loading rate. *for example, this is why you have nail guns - they succeed at a high rate on driving nails into concrete whereas trying to do the same job at a lower rate always fails. * Concrete is the issue. *Whack a nail into wood, or push it in with an arbor press, and it's about the same (although the whacked nail might hold better due to local heating of the wood resins). [snip] DearChalo, Usually I follow you because your posts are clear to even the meanest intelligence. But this is a concrete example (sorry, couldn't resist it) of how even you can overestimate the dregs of your readership. Can you explain concrete versus wood a little more from the nail gun's point of view? Concrete is very strong in compression, but subject to being disintegrated by shock. The shock created by a powder-fired fastener accomplishes what a similarly large but steady axial load on the same fastener can't, pulverizing a small zone around the nail and allowing it to penetrate. Without the shock, a nail pushed sufficiently hard would bend or break before penetrating the concrete enough to fasten to it. Wood is a resilient material and does not need to be shocked to allow a fastener to penetrate. Thus a nail can be shot, pounded, or simply shoved into place with comparable results in whichever case. Chalo |
#19
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Wheel deflection
On 2008-10-29, jim beam wrote:
On Tue, 28 Oct 2008 17:58:52 -0500, Ben C wrote: [...] Rate of change of momentum = force. Force yields things. Rate of change of force is rate of change of rate of change of momentum. So that's just the rate at which you yield your rim. Since we aren't talking about hammering nails into concrete or making spoons, the rate of change of force probably doesn't make much difference to how much the rim yields in this case. in this case. but it's not a blanket statement - different materials have different deformation characteristics depending on rate. remember silly putty? Yes, I loved that stuff. I didn't know that stainless steel was more ductile at high rates. Although presumably you draw it with more or less constant force (reducing it as the wire gets thinner?), but at a high rate of displacement. |
#20
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Wheel deflection
On Wed, 29 Oct 2008 03:38:21 -0500, Ben C wrote:
On 2008-10-29, jim beam wrote: On Tue, 28 Oct 2008 17:58:52 -0500, Ben C wrote: [...] Rate of change of momentum = force. Force yields things. Rate of change of force is rate of change of rate of change of momentum. So that's just the rate at which you yield your rim. Since we aren't talking about hammering nails into concrete or making spoons, the rate of change of force probably doesn't make much difference to how much the rim yields in this case. in this case. but it's not a blanket statement - different materials have different deformation characteristics depending on rate. remember silly putty? Yes, I loved that stuff. I didn't know that stainless steel was more ductile at high rates. indeed it is. large deep drawn stainless is often explosive formed to get the job done. a traditional cold drawing process can be long, tedious, and not achieve the required deformation despite multiple phases of work. this is not limited to stainless - many structural materials can be formed in this way Although presumably you draw it with more or less constant force (reducing it as the wire gets thinner?), but at a high rate of displacement. wire is a different story - wire drawing is done at a fraction of the rate above. and it's easy to reduce progressively [and anneal between operations] to achieve the required total deformation. |
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