what causes this damage?

[Udonming]

YY NanoSpeed 4500, glad the owner only cut the strings and when I found I couldn't pull the center string then I realized this.

[Alexccs]

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 ?

I agree with yan.v that the possible cause of the crack are the excess tension which the frame did not made to handle those tension. In my collection I have a ISO 800 tour, was great with 26 lbs until I put it to 28 lbs, it crack like Kwun picture.

[silentheart]

I agree with yan.v that the possible cause of the crack are the excess tension which the frame did not made to handle those tension. In my collection I have a ISO 800 tour, was great with 26 lbs until I put it to 28 lbs, it crack like Kwun picture.

Looks like no load spreader was used?

[zombie0517]

I has seen this type of crack as well. Cracked @ 6 O'clock. BG65 @ 22 lbs on an old Impact racquet

[Blitzzards]

Personally I believe the racquet has been strung several times using a clamp down machine, where the previous stringers have clamped down too tightly.

I don't see the sign of a cave in at the middle of the centre main strings like the one posted by Alexccs so we can rule that out, especially when the racquet was done using the Yonex ES5Protech which comes supplied with the H-shaped load spreader.

How does the top side of the racquet frame look like?

[dunmaster]

so bad to see so many cases like this!

also curious to know whether any one has NON-Yonex racket cracked like this.

[R20190]

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.

Warranty doesn’t really come into it imo. In the UK our bridges are generally designed for 120 years – but that is not to say they won’t fail or show signs of failure before that time. You could buy a brand new racquet and break it on the first string job. It’s the same with everything, you could buy a new TV with 2 years warranty and have it die within the first week. Warranty does not guarantee against defect or design flaws. In a way, it is the reason why we have warranties, because there can be discrepancies in manufacturing etc.

Anyway, a structure is a structure. Sure, different materials behave differently but the fundamentals of structural mechanics is the same. So a structural engineer who may have practiced in designing in steel and concrete all his life can turn his hand to designing in aluminium, composites etc without too much trouble. I remember when I started designing with carbon fibre 10yrs ago – there was a new learning curve for me, but you can still understand how it works.

Back to topic, kwun’s photo shows a crack on the inside of the frame. Without hooking up stress/strain gauges or alike, perhaps even do a FEA analysis on the racquet it’s difficult to tell what the failure mode is. It’s certainly not obvious to me looking at it what caused it to crack in that way. I would expect the more likely scenario where cracks are on the outside of the frame like Udonming’s photo where the load transfer from the string on to the grommet and into the frame would cause a shearing effect wedging and splitting the carbon between the holes as shown below. I’m obviously showing a simplified representation of a racquet frame, but for purposes of illustration...



In Kwun’s case, whilst the whole frame should generally be in compression in the cross-sectional plane, the only plausible failure mechanism I can think of is perhaps as shown below. The grey reaction arrows are not external reactions, but internal reactions from the frame in the longitudinal direction (into the image). This would effectively form a simply supported beam, with max bending moment at the centre, causing tension at bottom of the box section. Now since the row of holes at the bottom creates a predetermined line of weakness in the box section, couple this with tension (blue arrows) at the bottom, the splitting of the fibres sideways seems possible to me that this is what caused the failure. Crushing at the top is possible too...

So, although I can’t be completely sure whether my theory is correct, but if we assume it is and that the racquet was not mistreated (e.g. excessive over-tensioning), the reason for its failure in this manner could be a manufacturing imperfection which introduced a weakness in the material fibres or it could be that the design did not cater for it sufficiently? Who knows? Just my 2 pence (or if 2 cents for you guys in the states)

[silentheart]

To R20190,
Thank you. I think I know where the problem is now. I know exactly where Evil Empire need to mod the process to improve on this issue. Thank you for the pictures. They speaks >1000 words.
Sorry for other members, I can not tell you what the issues is. I only hope this finding will improve the process better.

[chandsj]

it was happened once with my Ti 10 here in Chennai, India with Babolat sensor machine. the main reason is too tight at 6 and 12 oclock site. When the crosses doen the crack will develop even after fininshing stringing
.

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

Attachment 117077

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?

[canti]

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?

66um 26lbsReplaced 2 grommets.

[canti]

Personally I believe the racquet has been strung several times using a clamp down machine, where the previous stringers have clamped down too tightly.

I don't see the sign of a cave in at the middle of the centre main strings like the one posted by Alexccs so we can rule that out, especially when the racquet was done using the Yonex ES5Protech which comes supplied with the H-shaped load spreader.

How does the top side of the racquet frame look like?

No damage on the top side it might have been from previous stringing. I borrowed it from a good friend of mine because it was just sitting in his bag. I had my other friend string it with a ES5protech so I'm assuming it was damage from another stringer because she hasn't had any problems so far stringing.