Hi,
How is this measured, and to what degree of accuracy? How do you obtain this value over a range of temps (do you put the tyre in a thermal chamber and leave it to soak for a short while, then take a hardness reading, or is there a dynamic measurement of some other parameter taken and related back to hardness?).
How is Tyre Hardness Verified?
Started by
MarkWill
, Jul 17 2004 13:10
8 replies to this topic
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#2
nicholasc
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Posted 18 July 2004 - 03:29
I don't think the actual hardness value is that important. Teams may refer to tyres as soft or hard but I'd imagine (I have no first hand knowlege) that it's a categorisation applied by the tyre companies in F1 to mask what they're really concerned with, which is the comparative values of the various active chemicals and fillers in the casing and carcass.
there are a number of hardness tests commonly used. I'm not sure they're actually used in terms of race car rubber. Try here for more basic information: google
there are a number of hardness tests commonly used. I'm not sure they're actually used in terms of race car rubber. Try here for more basic information: google
#3
MarkWill
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Posted 18 July 2004 - 15:35
Hi Nicholasc,
Thanks for replying. I'm very familiar with the standard hardness tests, which is why I'm intrigued by the application of the term to tyres. I see that the quality of hardness must mean something a bit more abstract, but I'm not sure what it is. If it means "resistance to abrasion" thats one quality that I suppose you actually can get from a hardness test. If it means also that there is a certain peel strength at the rubber/road surface interface then thats someting else, but that could also be thrown into the hardness definition. This quality changes with temperature, and I'm wondering how it is characterized (using what test setup, and to what degree of accuracy?)
Mark
Thanks for replying. I'm very familiar with the standard hardness tests, which is why I'm intrigued by the application of the term to tyres. I see that the quality of hardness must mean something a bit more abstract, but I'm not sure what it is. If it means "resistance to abrasion" thats one quality that I suppose you actually can get from a hardness test. If it means also that there is a certain peel strength at the rubber/road surface interface then thats someting else, but that could also be thrown into the hardness definition. This quality changes with temperature, and I'm wondering how it is characterized (using what test setup, and to what degree of accuracy?)
Mark
#4
Greg Locock
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Posted 18 July 2004 - 23:56
Rubber is all rules of thumb. Wear is measured by buffing type tests, for which you get a certain weight loss per unit time, running a block against a belt sander. Dry grip is measured on a friction rig (don't know how, probably ad hoc). Wear and dry friction both tend to track with changes in hardness, for similar compounds.
I thought there were SAE standard tests, but my ancient copy of the standards doesn't have them.
I thought there were SAE standard tests, but my ancient copy of the standards doesn't have them.
#5
MarkWill
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Posted 19 July 2004 - 01:17
Hi Greg,
Thanks for the insight. I guess that explains all of the tyre testing - it must be horrendously wasteful and, if the temperatures are off, could result in a total waste of time when the teams are aiming at getting data. I guess that also explains a bit of the Ferrari edge - their private track must be a great "controlled" test bed.
I have never seen a friction rig - it may sound daft, but what parameters does it measure (temperature at the mating surface? load vs. static friction?). In my naivete I thought that perhaps the tyre companies looked at a combination of deflection of some standard test sample but I can see the practical side of the sander (still, it must be fairly arbitrary - I guess it depends on the surface roughness of the sander, plus the tyre roughness, plus what direction you sand in (and do you introduce changes in the sanding direction?).
Mark
Thanks for the insight. I guess that explains all of the tyre testing - it must be horrendously wasteful and, if the temperatures are off, could result in a total waste of time when the teams are aiming at getting data. I guess that also explains a bit of the Ferrari edge - their private track must be a great "controlled" test bed.
I have never seen a friction rig - it may sound daft, but what parameters does it measure (temperature at the mating surface? load vs. static friction?). In my naivete I thought that perhaps the tyre companies looked at a combination of deflection of some standard test sample but I can see the practical side of the sander (still, it must be fairly arbitrary - I guess it depends on the surface roughness of the sander, plus the tyre roughness, plus what direction you sand in (and do you introduce changes in the sanding direction?).
Mark
#6
random
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Posted 19 July 2004 - 05:06
I don't know about thermal chambers and all that, most racers I know just use a Durometer.Originally posted by MarkWill
Hi,
How is this measured, and to what degree of accuracy? How do you obtain this value over a range of temps (do you put the tyre in a thermal chamber and leave it to soak for a short while, then take a hardness reading, or is there a dynamic measurement of some other parameter taken and related back to hardness?).
They're about the size of a stop-watch and have a spring-loaded needle sticking out of the bottom. Push the device against a tire and notate the reading. The reading varies depending on how far the needle penetrates the tire.
I've got one around here somewhere, they seem to work fairly well.
http://www.pitstopus...CategoryID=1517
#7
MarkWill
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Posted 19 July 2004 - 10:38
Hi Random,
This is what I found from this article http://www.matweb.co...re-hardness.asp on the web (taken from Matweb.com).
(Quote)
"The Shore hardness is measured with an apparatus known as a Durometer and consequently is also known as 'Durometer hardness'. The hardness value is determined by the penetration of the Durometer indenter foot into the sample. Because of the resilience of rubbers and plastics, the indentation reading may change over time - so the indentation time is sometimes reported along with the hardness number. The ASTM test method designation is ASTM D2240 00. Related methods include ISO 7619 and ISO 868; DIN 53505; and JIS K 6301, which was discontinued and superceeded by JIS K 6253.
The results obtained from this test are a useful measure of relative resistance to indentation of various grades of polymers. However, the Shore Durometer hardness test does not serve well as a predictor of other properties such as strength or resistance to scratches, abrasion, or wear, and should not be used alone for product design specifications.
As seen in the charts below, the correlation between the two Shore Durometer hardness scales is weak; attempts at conversion between the scales are therefore discouraged. The correlation is higher for materials with similar resiliency properties, but is still too low for reliable conversions. Likewise, conversion between Shore Hardness and Rockwell hardness is discouraged."
Sorry, I couldn't copy the scales, but if you check the link you will see what they mean. Ok, I see how the "hardness" is measured on track but it doesn't seem necessary to do laps to get that information (you could just manufacture the tyre, heat it up and take it out of the oven and use the durometer to measure the hardness changes as it cools down). Is there a tie-in between the Shore method and the abrasion measurement indicated by Greg?
This is what I found from this article http://www.matweb.co...re-hardness.asp on the web (taken from Matweb.com).
(Quote)
"The Shore hardness is measured with an apparatus known as a Durometer and consequently is also known as 'Durometer hardness'. The hardness value is determined by the penetration of the Durometer indenter foot into the sample. Because of the resilience of rubbers and plastics, the indentation reading may change over time - so the indentation time is sometimes reported along with the hardness number. The ASTM test method designation is ASTM D2240 00. Related methods include ISO 7619 and ISO 868; DIN 53505; and JIS K 6301, which was discontinued and superceeded by JIS K 6253.
The results obtained from this test are a useful measure of relative resistance to indentation of various grades of polymers. However, the Shore Durometer hardness test does not serve well as a predictor of other properties such as strength or resistance to scratches, abrasion, or wear, and should not be used alone for product design specifications.
As seen in the charts below, the correlation between the two Shore Durometer hardness scales is weak; attempts at conversion between the scales are therefore discouraged. The correlation is higher for materials with similar resiliency properties, but is still too low for reliable conversions. Likewise, conversion between Shore Hardness and Rockwell hardness is discouraged."
Sorry, I couldn't copy the scales, but if you check the link you will see what they mean. Ok, I see how the "hardness" is measured on track but it doesn't seem necessary to do laps to get that information (you could just manufacture the tyre, heat it up and take it out of the oven and use the durometer to measure the hardness changes as it cools down). Is there a tie-in between the Shore method and the abrasion measurement indicated by Greg?
#8
LS 1
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Posted 21 July 2004 - 21:34
Okay, so what does resistance to indentation have to do with performance? Seems like nothing directly, so at best it is a measure with an indirect correlation to what the mfg's and teams are really concerned about? E.g., a harder tire might conform less to the road surface (at equal psi, anyway) and thus offer less grip? Or have I just answered my first question?
#9
Greg Locock
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Posted 22 July 2004 - 00:16
There is only a very crude correlation - it is probably reliable for small changes in compounding and heat treatment.
Roughly speaking:
the more carbon black you have in a rubber then it gets stiffer (ie its young's modulus increases), more abrasion resistant, has a lower elongation at failure, is stronger (or weaker!), and it has more damping. Its durometer, which by definition is related to stiffness, will also increase.
I'd point out that on a typical rubber sheet I can get errors of 5 duro, and you'll get different measurements if you use different thicknesses, and the shape of the sample matters, and you need to do it on a flat hard surface.
In other words once a tyre is built it is VERY hard to measure its Duro, unless you cut a sample off again. What you do is measure the rubber before it gets moulded.
Roughly speaking:
the more carbon black you have in a rubber then it gets stiffer (ie its young's modulus increases), more abrasion resistant, has a lower elongation at failure, is stronger (or weaker!), and it has more damping. Its durometer, which by definition is related to stiffness, will also increase.
I'd point out that on a typical rubber sheet I can get errors of 5 duro, and you'll get different measurements if you use different thicknesses, and the shape of the sample matters, and you need to do it on a flat hard surface.
In other words once a tyre is built it is VERY hard to measure its Duro, unless you cut a sample off again. What you do is measure the rubber before it gets moulded.
