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PostPosted: Thu Aug 15, 2013 10:15 pm 
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Joined: Thu Jan 08, 2009 12:16 pm
Posts: 157
Location: Melbourne Australia
stephen@fibre-lyte wrote:
Tbh, I don't get involved too much with the repairs at our place, John (our special projects director) does them all and his workmanship is better than any I have seen. I've never seen him scrap a frame due to a handlebar cracking a top tube. To give you an idea of his talents he's built a time trial frame, a time trial wheel set and two mountain bikes from scratch as well as a hill climb car and a carbon tubbed sprint car that's currently being built.


Some things are better to be scrapped and not repaired, regardless of the skill and I am sure John has plenty of skill, respect.

Top tubes in particular are so thin these days that with higher mod fibre and a lower ILS resin the delam travels. If the majority of the tube is delaminated there is no sound material to scarf a repair into. Sure it may be technically possible to repair, however it gets to a stage where it is not practical or cost effective. This is why we use ultrasound to verify the condition of the material before deciding if a repair is practical.

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Specialist Sports Technology
http://www.luescherteknik.com.au
Zerocompromise High Performance Footwear
http://www.zerocompromise.com.au
Carbon Bike Repairs
http://www.carbonbikerepair.com.au


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PostPosted: Sat Aug 17, 2013 12:15 am 
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I'd agree with you if I thought that there was a danger to the rider and the repair was unsafe. However, I'd hate to see a £2k frame scrapped when it could be safely repaired. In all our years of repairing frames we've never had a frame brought back in when a repair hasn't worked. When would you deem that a frame isn't cost effective to repair? Say for instance a £1.5k to £2k frame?

As you quite rightly say, tubes are very thin these days so how would ultrasound benefit? For thicker materials ultrasound can certainly be of benefit to detect both voids and delamination but for very thin tubes I'd imagine that any delamination would be visually obvious, without the need for ultrasound? to be perfectly honest, from the frames I've seen John repairing recently, when he rubs away the paint to do the repair, it seems that he has to clear away an awful lot of filler at the same time!

I'm curious about your comments of the materials, why do you suggest that lower ILS resins are used?

Despite having worked in the carbon fibre industry for the last 15 years, I'm still learning new technologies and techniques every day. I love my job! :D


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Posted: Sat Aug 17, 2013 12:15 am 


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PostPosted: Sat Aug 17, 2013 8:59 am 
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Joined: Mon Jul 13, 2009 9:19 pm
Posts: 255
Location: Denmark
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My Cervelo R3 from 2008 suffered at blow in the top tube april this year and had it fixed by insurrance. I didn't want the fix to be invisible, it is like a battlescar. It actually to me 2 days to notice the crack and I did when I wanted to wash it. I have ridden this frame just like I did before, I have hit numerous pot holes, I'm jumping up and down curbs when I need to. That crack of yours is minimal, if I put my thumb in the damaged part it was softer. I would get that fixed and ride it, I would have fixed my own bike even I have had to pay for it my self


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PostPosted: Wed Aug 21, 2013 9:58 pm 
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Joined: Thu Jan 08, 2009 12:16 pm
Posts: 157
Location: Melbourne Australia
stephen@fibre-lyte wrote:
As you quite rightly say, tubes are very thin these days so how would ultrasound benefit? For thicker materials ultrasound can certainly be of benefit to detect both voids and delamination but for very thin tubes I'd imagine that any delamination would be visually obvious, without the need for ultrasound? to be perfectly honest, from the frames I've seen John repairing recently, when he rubs away the paint to do the repair, it seems that he has to clear away an awful lot of filler at the same time!

I'm curious about your comments of the materials, why do you suggest that lower ILS resins are used?

Despite having worked in the carbon fibre industry for the last 15 years, I'm still learning new technologies and techniques every day. I love my job! :D



Ultrasound is very useful for thin tubes as the delam can travel a long way from the original impact site. You cannot see this visually except when you are grinding away the damage. You need a certain amount of sound material around the damage for the repair to bond to, the ultrasound scan can verify this easily. The resolution on my ultrasound system is about 0.1mm, the thinnest regions are about 0.7mm, more typical is about 1.0mm.


I know what you mean, I started over 20 years ago and feel the same way, when you stop learning it is time to retire.

_________________
Specialist Sports Technology
http://www.luescherteknik.com.au
Zerocompromise High Performance Footwear
http://www.zerocompromise.com.au
Carbon Bike Repairs
http://www.carbonbikerepair.com.au


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PostPosted: Thu Aug 22, 2013 12:58 am 
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Joined: Thu May 29, 2008 12:22 am
Posts: 596
I'd be curious to see an ultrasound image vs a visual mage to see how the two compare in terms of visible delamination. How many layers would you expect to see in a wall thickness between 0.7mm and 1.0mm? I imagine no more than four or five depending on the fibre used which means that the outside layers must be peeling away from the central layers, especially as the outer layers are usually at least 200g plain weave or 2x2 twill which will be around 0.2 to 0.3mm thick. If the outer layers are delaminating then from the point of impact you should be able to see the non flexible paint or lacquer cracking. i can't imagine that the central layers are delaminating from a point of impact without any visible signs on the outer layers, I'm not even sure how that could happen but feel free to explain it.


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