what causes this damage?

***kwun*** · 02-22-2012, 02:51 PM

a friend of mine has this damage in his racket, a current gen AT700, near 12 o'clock.

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i was told it was strung with a ES5Protech.

i originally thought if it were done with a clampdown, it maybe the clamps were too tight, but ES5PT is a suspension, so that rules that out.

any idea what the stringer did wrong?

**silentheart** · 02-22-2012, 03:24 PM

Never seen on like this. Need more info on this. My guess is material fatigue.
1) is string NBG98?
2) grommets looks different than my brand new unstrung at700. can you verify the gromment has been replaced before?

**Fidget** · 02-22-2012, 07:41 PM

Brutal grommet extraction sounds a reasonable source of injury.
Pardon my inexpertise, but is it also possible that a load spreader, at some point during the stringing of the mains, was carrying too much pressure and weakened the inside of the frame? Then the lateral pressure of the tensioning crosses may have applied the coup de grace.

**Optiblue** · 02-22-2012, 07:58 PM

I'm going to guess that load spreaders were used, but the stringer overtightened the 12 and 6 o'clock mounting points. What tension, how old, and was it like that before it got strung up? I'm predicting a very narrow shaped frame~

**silentheart** · 02-22-2012, 08:23 PM

Sorry to ask stupid questions again.
1) was that a tie off or starting knot #3 from the left?
2) String could be ZyMax62 and making the grommets look too big?
3) The grommets in question are #4 and #7 from the left.

**yan.v** · 02-22-2012, 09:31 PM

The load spreader theory sounds unlikely. I really doubt that the frame would crack that way.

I would go for 1)Racket inperfection 2)Racket "fatigue" 3)Intense grommet extraction (seriously, they probably did it with a drill)

**dunmaster** · 02-22-2012, 09:44 PM

never seen this bad of a crack! any picture of the other side of the frame?

also, from the picture itself, if I see it from an angle, I saw a small "dented line" on the frame around the middle 4 grommets. If this is physically true, not the reflection issue, it would point to a bad mounting and / or load spreader.

whatever the reason is, it's a big "ouch".

**Alex82** · 02-22-2012, 11:48 PM

at the moment i don't have a racket to compare, but i think the grommets are to big in diameter. maybe the old grommets on 12 o clock was broken and he changed it with to big grommets...

**R20190** · 02-23-2012, 06:47 AM

Looks to me like an imperfection in the racquet.

If it were at a shared hole I would have said that someone had been over enthusiastic with an awl causing micro-fractures, exacerbated by tensioning... but as there aren't any shared holes, it looks likely to me that this is an manufacturing fault.

**Mark A** · 02-23-2012, 09:37 AM

Rackets normally crack across the frame, rather than along it, during stringing. Racket imperfection would be my vote as well.

**silentheart** · 02-23-2012, 10:00 AM

Originally Posted by Mark A

Rackets normally crack across the frame, rather than along it, during stringing. Racket imperfection would be my vote as well.

That would be my vote it is a new or near new racquet. However, from what I can see, this AT700 has been restrung several time before (my guess is more than 7 times already) If it is a defect, it would have shown very early, may be 2 or 3 restring jobs. I would like to know if ther gromment was ever replaced or turned.

**R20190** · 02-23-2012, 11:39 AM

Originally Posted by silentheart

If it is a defect, it would have shown very early, may be 2 or 3 restring jobs.

Not necessarily, it may be because of the cyclic loading and unloading effects of stringing that has gradually exposed a weak area of the racquet. Or perhaps, the stringer made a mistake and did not support the frame well enough on one occasion which revealed the defect.

Sometimes problems don't show up until much later, as a structural engineer I see a lot of failures occuring when structures are exposed to repeated loads, be it traffic, wind or even temperature effects. Sometimes it is a design flaw, other times it could be a quality or misuse issue... difficult to say in this instance.

**Valentinas** · 02-23-2012, 11:49 AM

5 prong load spreader and bad mounting.

Valentinas

**silentheart** · 02-23-2012, 12:00 PM

Originally Posted by R20190

Not necessarily, it may be because of the cyclic loading and unloading effects of stringing that has gradually exposed a weak area of the racquet. Or perhaps, the stringer made a mistake and did not support the frame well enough on one occasion which revealed the defect.

Sometimes problems don't show up until much later, as a structural engineer I see a lot of failures occuring when structures are exposed to repeated loads, be it traffic, wind or even temperature effects. Sometimes it is a design flaw, other times it could be a quality or misuse issue... difficult to say in this instance.

Agree with your assessments. And yes, paint offent time cover the issue and show up later. However, what you are describing is for a bridge or a structure designed for 10, 20 or more yr of life time. However, yy racquet has 1 year warranty against defect. If you break the string of a specific racquet everyday and restrung every night, sorry, that is a little extreme case. But warranty will still apply given that you do not abuse the racquet and maintain the racquet in a good condition and no clash. To me, it looks more like a tube crack under vertical load to me in this picture. I am not sure if the racquet has always been strung with a ES5ProTech or a suspension mount machine.

I would like to hear you opinion on this one. In this case of AT700 crack. What is your thought.

**Valentinas** · 02-23-2012, 12:10 PM

I have similar photo of AT700 taken by myself. Note that cracks are developing between the grommets.

Valentinas

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**silentheart** · 02-23-2012, 12:12 PM

Originally Posted by Valentinas

I have similar photo of AT700 taken by myself. Note that cracks are developing between the grommets.

Valentinas

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There are crack on the 2 left grommet too. WOW. Thanks!

**yan.v** · 02-23-2012, 12:34 PM

Looking at these pictures, I think that it could be possible for the cracks to be caused by a too great tension on the mains. I could really see this as an additional effect from excessive tension (the other being racket deformation). I do think that the rackets would have had to have some kind of imperfection or weakness, considering how rare it is to see such damage.

What tension are these rackets usually strung at ?