The ultimate tension loss measurement

[stoneage]

Originally Posted by newyorkstadium

Great stuff, stoneage.

The string only loses 1.2kg through 6-8 hours playing time and 4.6kg at rest. It also looks like it has practically stopped losing tension through playing, by the end. This seems to indicate that most of tension loss doesn't come from hitting. Does this mean the best way to compare the tension loss of two strings is the loss at rest?

Would the string have lost a lot more tension if you had done more hitting at the 120 hour stage?

The string loses tension over time. If you apply an extra load, e.g. by playing, this process is accelerated. So yes, if I would have started to play earlier, say 1 hour per day from day one, the tension would have dropped quicker. But my guess is that the final tension after 5-6 weeks would have been about the same.

When a string is loaded during stringing the molecules start to glide relative to each other causing a permanent deformation (and stress relaxation). This "gliding" however, becomes more difficult the more the string is deformed, which means that the tension loss slows down. This typical for most visco-elastic materials

A simple model is to view the string as two springs and one damper:



When you load the string during stringing both springs are stretched to take up all the load since the damper is rigid (a fast action). The damper will then start to glide, which means that spring E2 is relaxed. Eventually the damper has relaxed E2 completely and the system has settled to a lower tension caused by the stretching of E1 only.

I was just comparing this to the TWU data on the Proline II 1.25 mm. In the TWU data the static loss is 8lbs and the total loss is 22lbs. Why is the total loss much higher? The TWU static loss is tested sixty seconds after pulling. At the 0 hrs stage yours is 4.6lbs. Does this mean the TWU data is unreliable?

No, it is not necessarily contradictory. The curve only shows the tension after the stringing was finished, so the string had already lost a couple of kg. The stringing took almost 1 hour since I was measuring on the same time and had a couple of measuring cables to handle when rotating the racquet. How much it lost during this first hour is difficult to say since there are several effects causing a change in the tension. See this thread:
http://tt.tennis-warehouse.com/showthread.php?t=397033

Sten

__________________________________________________ _________
racquetTune, stringBed and swingTool racquet apps for the iPhone/iPad.

[newyorkstadium]

So the 0 hour stage is 1 hour after the stringing process. The curve starts at 20.9, suggesting the string lost 2.1kg through stringing. Is this correct?

Sorry, I don't understand the tension variation thread you've linked. It seems to suggest tension loss is very high after pulling, then rises again 35 mins after. Does this mean the TWU static loss is unreliable because they measure too early?

Why is the total tension loss so high for the TWU data? In there data, the pro line II loses 22lbs, or 9.98kg. This is a lot more then the total tension loss of 5.8kg in your graph. Does this mean there testing method is too aggressive?

Is the best way to compare the tension loss of two strings to look at the static loss? In your graph, the string only loses 1.2kg through playing time and 4.6kg at rest.

[stoneage]

Originally Posted by newyorkstadium

So the 0 hour stage is 1 hour after the stringing process. The curve starts at 20.9, suggesting the string lost 2.1kg through stringing. Is this correct?

Yes and no. It is correct that the the string lost 2.1 kg. But on the same time tension was added buy pulling the crosses so the loss would have been higher in a single string.

Sorry, I don't understand the tension variation thread you've linked. It seems to suggest tension loss is very high after pulling, then rises again 35 mins after. Does this mean the TWU static loss is unreliable because they measure too early?

You can't compare the two. TWU measures the material data, I measured what happened in a racquet during stringing. What you see in the tension variation thread are the effect of three things: Creep/stress relaxation in the string, racquet head deformation and string elongation from crosses.

When you string the mains they lose tension because the material loses tension, but also because the the racquet head is deformed. This is what is showed in the first half of the curve. Then you start to pull the crosses. The mains get longer because of the "wavy" form of the stringed racquet. This elongation increases the tension. The crosses will also negate some of the head deformation which further increase the tension. Without pulling the crosses the tension would have continued to fall.
http://appmaker.se/?m=4&s=5

Why is the total tension loss so high for the TWU data? In there data, the pro line II loses 22lbs, or 9.98kg. This is a lot more then the total tension loss of 5.8kg in your graph. Does this mean there testing method is too aggressive?

If you add an 3 kg tension increase from the crosses you end up with similar figures in both cases.

Is the best way to compare the tension loss of two strings to look at the static loss? In your graph, the string only loses 1.2kg through playing time and 4.6kg at rest.

As I said in my last reply the reason for this difference is that I waited to play so I think that a combination of static and dynamic data as TWU does it is valid.

[newyorkstadium]

I still wonder, with the TWU testing procedure being quite short (I think), will strings continue to lose tension after the test. So, if two strings have a similar total tension loss on the TWU data, but one has higher static loss, one has higher dynamic loss. In the future won't the string with higher dynamic loss lose more tension? Thus the string with same total loss, but higher static loss, is better.

Originally Posted by stoneage

If you add an 3 kg tension increase from the crosses you end up with similar figures in both cases.

How do I add the 3kg tension increase from the crosses using the TWU performance database? If I bump up the reference tension 10lbs, the total loss only decreases 0.3kg, or 0.7lbs

[Povl Carstensen]

Highly interesting, thank you!
Would be great to see it for syn gut, and gut...

[Povl Carstensen]

Deleted
10chx

[newyorkstadium]

Originally Posted by newyorkstadium

I still wonder, with the TWU testing procedure being quite short (I think), will strings continue to lose tension after the test. So, if two strings have a similar total tension loss on the TWU data, but one has higher static loss, one has higher dynamic loss. In the future won't the string with higher dynamic loss lose more tension? Thus the string with same total loss, but higher static loss, is better.

How do I add the 3kg tension increase from the crosses using the TWU performance database? If I bump up the reference tension 10lbs, the total loss only decreases 0.3kg, or 0.7lbs

Also, corners reckons the TW tension loss tests are too aggressive. Their tests make copolys lose more tension than they would in the real world. Is this possible, baring in mind there seems to be a limit to how much tension a string can lose?

Thanks for your help.

[stoneage]

Originally Posted by newyorkstadium

Also, corners reckons the TW tension loss tests are too aggressive. Their tests make copolys lose more tension than they would in the real world. Is this possible, baring in mind there seems to be a limit to how much tension a string can lose?

Thanks for your help.

I don't really know enough about the TWU test to have a definite view of its validity.

But in general, creep and stress relaxation in a material is a highly non linear phenomenon, which makes it difficult to accelerate tests. A high load under a short time doesn't have the same effect as a low load under a long time. You would need several material constants to describe the material. Even the much simplified model with two springs and a damper I showed in the earlier post leads to three material constants that needs to be measured, and a fairly complex equation to calculate the tension drop. An equation that I very much doubt that 99.99% of stringers/player wan't to concern themselves with (I wouldn't).

So you can't use a single value (the TWU tension drop) to exactly predict how much tension a racquet will loose, especially since it would differ if it is a recreational player playing once a week or a college player playing 2 hours a day. But you can use it to compare strings: A string with a high TWU value will probably lose tension quicker in practice than a string with low value. But you shouldn't bother about the decimals.

Sten

[newyorkstadium]

Originally Posted by stoneage

If you add an 3 kg tension increase from the crosses you end up with similar figures in both cases.

If I bump up the reference tension 10lbs, the total loss only decreases 0.3kg, or 0.7lbs, which is still way off your chart figures.

If the tension loss is similar, then by the end of the TWU procedure the tension loss would have all but stopped, right? This means I can use the total tension loss figure. Otherwise, if the racket still has a lot of tension loss to go, I should use the rate of loss (static loss deducted from total loss).

[stoneage]

Originally Posted by newyorkstadium

If I bump up the reference tension 10lbs, the total loss only decreases 0.3kg, or 0.7lbs, which is still way off your chart figures.

What reference tension?
In my set up I strung the racquet with 23 kg setting on the machine. Adding 3 kg from pulling crosses into the mains means that initial tension was something like 26 kg, giving a total tension drop of 9 kg. However, the extra 3 kg was just an educated guess, it could have been 2 kg or 4 kg.

I am saying this again: You can NOT compare the tension in my test with the TWU figure since they represent two very different situations.

If the tension loss is similar, then by the end of the TWU procedure the tension loss would have all but stopped, right? This means I can use the total tension loss figure. Otherwise, if the racket still has a lot of tension loss to go, I should use the rate of loss (static loss deducted from total loss).

I hope you don't think that the TWU figure gives you the tension loss in a racquet? (because it certainly doesn't)

[newyorkstadium]

Originally Posted by stoneage

What reference tension?
In my set up I strung the racquet with 23 kg setting on the machine. Adding 3 kg from pulling crosses into the mains means that initial tension was something like 26 kg, giving a total tension drop of 9 kg. However, the extra 3 kg was just an educated guess, it could have been 2 kg or 4 kg.

I am saying this again: You can NOT compare the tension in my test with the TWU figure since they represent two very different situations.

I hope you don't think that the TWU figure gives you the tension loss in a racquet? (because it certainly doesn't)

I mean't tension loss in the strings, not the racquet.

For the TWU performance database, is it more useful to use rate of loss (total loss minus static loss) then total tension loss? This allows you to see how much tension a string loses post-stringing, either through hitting or at rest. So a string with more rate of loss will ultimately lose the most tension. This is what I have been doing in the past.

[newyorkstadium]

bump......

[tlm]

Sure is a lot of trouble for nothing really. I already know that my strings play the best the first day or 2 and then they go down some and stay about the same.

I only use them for a week anyway and then change them. I don't need to measure tension loss, I can see the difference in how my strings play as they lose tension. Plus I already know that nothing beats poly when it is new.

[newyorkstadium]

Originally Posted by tlm

Sure is a lot of trouble for nothing really. I already know that my strings play the best the first day or 2 and then they go down some and stay about the same.

I only use them for a week anyway and then change them. I don't need to measure tension loss, I can see the difference in how my strings play as they lose tension. Plus I already know that nothing beats poly when it is new.

I use multi's. I don't break them, so I like to use them for 2-3 months. I'll buy a tension meter myself and find out how much tension strings are losing post stringing, and when they stabilize. I've been curious about this for ages.

[newyorkstadium]

Originally Posted by stoneage

The string loses tension over time. If you apply an extra load, e.g. by playing, this process is accelerated. So yes, if I would have started to play earlier, say 1 hour per day from day one, the tension would have dropped quicker. But my guess is that the final tension after 5-6 weeks would have been about the same

Originally Posted by stoneage

But in general, creep and stress relaxation in a material is a highly non linear phenomenon, which makes it difficult to accelerate tests. A high load under a short time doesn't have the same effect as a low load under a long time. You would need several material constants to describe the material. Even the much simplified model with two springs and a damper I showed in the earlier post leads to three material constants that needs to be measured, and a fairly complex equation to calculate the tension drop. An equation that I very much doubt that 99.99% of stringers/player wan't to concern themselves with (I wouldn't).

So you can't use a single value (the TWU tension drop) to exactly predict how much tension a racquet will loose, especially since it would differ if it is a recreational player playing once a week or a college player playing 2 hours a day.

These two quotes contradict each other. The top quote suggests the final tension loss will be the same regardless of load. The bottom suggests the load impacts how much a string loses, and when it stabilizes.

[tlm]

Originally Posted by newyorkstadium

I use multi's. I don't break them, so I like to use them for 2-3 months. I'll buy a tension meter myself and find out how much tension strings are losing post stringing, and when they stabilize. I've been curious about this for ages.

Wow you can use mult's for 2-3 months thats a long time.

[stoneage]

Originally Posted by newyorkstadium

These two quotes contradict each other. The top quote suggests the final tension loss will be the same regardless of load. The bottom suggests the load impacts how much a string loses, and when it stabilizes.

No, they don't.
The first one says that my guess is that they would eventually end up the same (or at least similar).

The second statement talks about about how much a string loses, that is correct. But it doesn't say what would happen eventually. It just says that how fast a string will loose tension depends on the load.


If you look at the spring and damper model again (which is actually good for understanding what happens): As I wrote "Eventually the damper has relaxed E2 completely and the system has settled to a lower tension caused by the stretching of E1 only." But if you stretch the string a little extra by playing during that process, both springs will be stretched and the load increased. That will lead to the damper being pulled a little extra. When the deformation is back to normal the damper is therefore more elongated, E2 is more relaxed and the total tension is lower. The tension loss is thus accelerated. But the end result is the same (E1 carrying all load), it is only the time to reach that state that will differ.

Sten

__________________________________________________ _________
racquetTune, stringBed and swingTool racquet apps for the iPhone/iPad.

[newyorkstadium]

Thanks. I think I understand the damper model. Does tension loss stabilize at a similar point, regardless of how much you accelerate the loss/increase load?

In another thread, corners stated "I believe TWU's procedure for tension loss measurement is too aggressive. Basically, their tests make the co-polys lose more tension than they would in the real world". Is this false?

[stoneage]

Originally Posted by newyorkstadium

Thanks. I think I understand the damper model. Does tension loss stabilize at a similar point, regardless of how much you accelerate the loss/increase load?

The model says it does. However, it is a simplified model so real materials might behave differently. But I think it is a reasonable assumption as long as the acceleration consist of playing more or less often.

In another thread, corners stated "I believe TWU's procedure for tension loss measurement is too aggressive. Basically, their tests make the co-polys lose more tension than they would in the real world". Is this false?

I have never used the TWU tension data so I can't really comment on how good they are in practice. I have read the paper of the methodology of the test though and I was a little curious about the relative short testing time for something that essentially is a long time phenomena. Some materials exhibit a fairly quick initial tension loss and then a slower rate whereas others are more even. And these test risk to miss that difference. But doing real long time tests under different loads and temperatures would probably cost to much.

Since there are no other tension loss data available they are certainly better than nothing as long as you don't take every kg literally. And maybe you should only compare strings within the same category.

[newyorkstadium]

Okay. I have no more questions. Thanks for all the information.