#11
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rubber compounds
On Fri, 23 Feb 2018 03:36:30 +0100, Emanuel Berg
wrote: Jeff Liebermann wrote: https://www.bicycling.com/bikes-gear/components/know-your-rubber-quick-start-guide-mountain-bike-tire-design From the same paragraph as the above quote: Hysteresis A dynamic measurement of energy loss in the rubber compound, this can also relate to rolling resistance or tire "grip." A 70sA compound typically has little energy loss, while a 40sA has a large percentage of energy loss. BTW what notation is 70sA and 40sA? 70 Shore A and 40 Shore A. The "A" defines the type of penetrator used. A is for soft rubbers, while D is for hard. https://en.wikipedia.org/wiki/Shore_durometer#Durometer_scales There's a bit of a muddle over the term durometer. Some say it's the units of measure, some say it's the name of the instrument, and some say it's both. Methinks it's the instrument name. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
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#12
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rubber compounds
On Fri, 23 Feb 2018 03:34:42 +0100, Emanuel Berg
wrote: So the viscoelastic property is what makes the tire deform/recover as it rolls in under/away from the weight of the bike&rider, and this is hysteresis, and the result is loss of energy (as heat), and this is one component of overall loss of energy which is bunched together as rolling resistance? No. The visoelastic means that the material can be both viscous and elastic at the same time. Apply some force and viscous materials flow or ooooze. Elastic materials compress under the same force, but return to their prior state when the force is removed. Rubber follows a hysteresis curve such as: https://revisionworld.com/a2-level-level-revision/physics/force-motion/solid-materials/rubber or: https://www.google.com/search?q=rubber+hysteresis+loop&tbm=isch The area inside the loop represent the energy converted to heat by rolling down the road. The largest factor in rolling resistance is this energy loss. There's a section in the Bicycle Science 3rd edition book covering the details of measuring rolling resistance I should get that book... The first and 3rd editions are quite different. Methinks that 3rd is the best, but there was quite a bit of interesting stuff deleted from the first. I have both. https://www.alibris.com/Bicycling-Science-David-Gordon-Wilson/book/17828968 Maybe disintegrate a tire and put a piece of it in a stand or a vice? Or/and perhaps fixate the durometer as well, like a shop drill? Yuck. You'll find that a bicycle tire under pressure produces a slightly different hardness measurement than one laid flat on a table. The thinner the tire, the larger the difference. You want the hardness under operating conditions, which means inflated and with a rider on the bicycle. Again, the difference is not huge, but it is measurable. BTW how do ISO/ETRTO measure the tire width? I've heard it is from one bead, over the tread, to the other bead, this distance divided by 2.5? Do they also disintegrate the tire before doing this or do they use a string of some kind to loop around? I have no idea and am too lazy/busy/burned-out to look it up for you right now. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#13
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rubber compounds
On 2/22/2018 11:37 PM, Jeff Liebermann wrote:
On Fri, 23 Feb 2018 03:34:42 +0100, Emanuel Berg Rubber follows a hysteresis curve such as: https://revisionworld.com/a2-level-level-revision/physics/force-motion/solid-materials/rubber or: https://www.google.com/search?q=rubber+hysteresis+loop&tbm=isch The area inside the loop represent the energy converted to heat by rolling down the road. The largest factor in rolling resistance is this energy loss. I think that's an oversimplification at best, based on an inadequate definition of "rolling resistance." I say this because the easiest way to reduce that rubber hysteresis would be to completely do away with the rubber. Ride on metal tires, as did the wagons and carriages and "boneshaker" quasi-bicycles of 150 years ago. Bingo! No hysteresis loss! .... but tremendous rolling resistance compared to a pneumatic tire. There's a lot more to the phenomenon than hysteresis. -- - Frank Krygowski |
#14
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rubber compounds
Jeff Liebermann wrote:
There's a bit of a muddle over the term durometer. Some say it's the units of measure, some say it's the name of the instrument, and some say it's both. Methinks it's the instrument name. Sure sounds like it. But I suppose it could be a unit as well only first time I ever heard of it was in the context of a thing or gadget, at least that was the way I read it. "Use the durometer to determine the durometer!" -- underground experts united http://user.it.uu.se/~embe8573 |
#15
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rubber compounds
Jeff Liebermann wrote:
Rubber follows a hysteresis curve Aha, interesting! The energy loss is a function of stress and strain Stress is a force acting on a rock per unit area. ... Stress can cause strain, if it is sufficient to overcome the strength of the object that is under stress. Strain is a change in shape or size resulting from applied forces (deformation). Rocks only strain when placed under stress. [1] (OK, that makes sense except what are the "rocks" refered to?) Also, when an elastic material (rubber) is deformed but recovers, does that count as strain? Probably yes as otherwise that curve wouldn't be the one to describe it all? That curve happens for each/any point on the wheel for each rotation? Assuming the rider doesn't runt the bike into a brick wall or anything... I have no idea and am too lazy/busy/burned-out to look it up for you right now. Well, don't be stressed and absolutely not strained by these questions [1] https://www.youtube.com/watch?v=rRTvl7D9Ugw -- underground experts united http://user.it.uu.se/~embe8573 |
#16
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rubber compounds
On Fri, 23 Feb 2018 13:08:13 +0100, Emanuel Berg
wrote: Jeff Liebermann wrote: There's a bit of a muddle over the term durometer. Some say it's the units of measure, some say it's the name of the instrument, and some say it's both. Methinks it's the instrument name. Sure sounds like it. But I suppose it could be a unit as well only first time I ever heard of it was in the context of a thing or gadget, at least that was the way I read it. "Use the durometer to determine the durometer!" If you parse the word into duro meter, it is somewhat obvious that it refers to the instrument, not the units of measure. The problem is that the industry was not prepared for the lack of units of measure. There are plenty of measurements that have no units, such as ratios, proportions, indexes, modulus, mean opinion score for VoIP intelligibility, etc. https://en.wikipedia.org/wiki/Dimensionless_quantity That worked fine, until it hit the automotive industry, which was not quite accustomed to the concept. It sounded rather odd that a measure of rubber hardness should not have some unit of measure, usually named after the inventor or internationally, after a famous dead scientist. Normally, it would be called XX shore units or something similar, but not this time. Also normally, a standards committee would be assigned to sort this out, but apparently they're too busy creating new standards than to fix the existing ones. However, all is not lost. This article proclaims that: https://en.wikipedia.org/wiki/Shore_durometer The term durometer is often used to refer to the measurement as well as the instrument itself. Therefore, on the authority of the Wikipedia authors and editors, you are allowed to perpetuate the muddle. Before you ask, zero durometer means that you punched a hole in material under test and 100 means that the indenter needle didn't move. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#17
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rubber compounds
Jeff Liebermann wrote:
If you parse the word into duro meter, it is somewhat obvious that it refers to the instrument, not the units of measure. To me the intuition is the other way around: durometer = instrument, as in thermometer, hygrometer ... Before you ask, zero durometer means that you punched a hole in material under test and 100 means that the indenter needle didn't move. OK, but wouldn't that also depend on the thickness of the material? Or is "strength thru thickness" a fine way of doing it? -- underground experts united http://user.it.uu.se/~embe8573 |
#18
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rubber compounds
On Fri, 23 Feb 2018 20:02:06 +0100, Emanuel Berg
wrote: Jeff Liebermann wrote: If you parse the word into duro meter, it is somewhat obvious that it refers to the instrument, not the units of measure. To me the intuition is the other way around: durometer = instrument, as in thermometer, hygrometer ... Do you measure temperature in units of themometers? Do you measure humidity in units of hydrometers? Before you ask, zero durometer means that you punched a hole in material under test and 100 means that the indenter needle didn't move. OK, but wouldn't that also depend on the thickness of the material? Or is "strength thru thickness" a fine way of doing it? Yes, it somewhat depends on thickness. If the "dent" produce goes though the material and pops out the other side, you'll get a much softer measurement than one that does NOT pop out the other side. Similarly, stacking up a pile of rubber sheets until the dent is totally inside the material, will produce something harder. I could try it now with some inner tubes, but I'm in a rush to collect on a free lunch. Maybe tonite. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#19
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rubber compounds
Jeff Liebermann wrote:
To me the intuition is the other way around: durometer = instrument, as in thermometer, hygrometer ... Do you measure temperature in units of themometers? Do you measure humidity in units of hydrometers? I mean, "durometer" sounds like "thermometer", "hydrometer", and so on (OK, it should be a "d" in English), so to me, it sounds like an instrument. Also, one might wonder why they felt the need to come up with a new unit for this at all! Couldn't it be "how much power to penetrate" or "how much power to reach a distance" or "how long a distance for a certain power"... (I say this without ever having used or even seen a durometer so maybe it doesn't make sense.) -- underground experts united http://user.it.uu.se/~embe8573 |
#20
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rubber compounds
Jeff Liebermann wrote:
Yes, it somewhat depends on thickness. If the "dent" produce goes though the material and pops out the other side, you'll get a much softer measurement than one that does NOT pop out the other side. Similarly, stacking up a pile of rubber sheets until the dent is totally inside the material, will produce something harder. For a material M, if you penetrate 1 distance unit at the cost of C, then go on to penetrate yet another distance unit (i.e. 2 in total), will the cost then be 2C for all of that? Or will the material, altho compromised (punctated and inflicted degree to some degree), retain some hindering or self-enforcing property to make the cost maybe 2^2C instead or something even higher? Wood for example, with a drill it is perhaps linear but chop a dagger into it and if it is thick you won't get anywhere except scratching the surface. -- underground experts united http://user.it.uu.se/~embe8573 |
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