Continued Bonding in Epoxy and Polyester Resins Over Time

[RiceAWay]

Now that they are using carbon fiber everywhere including in commercial aircraft can anyone give educated answers to what occurs to the bonding of the resins to the carbon fiber over time?

 

Of the bicycle failures I've see most of the failures occur after perhaps two or more years and the failure points do not show a clean break but more of a tearing which gives me the idea that the carbon fibers are losing their bonding to the resin. Of the failures that occur under two years the breaks appear to be clean as if there was a manufacturing error in which there was a bubble around which a fracture occurred.

 

Answers to these questions could affect everything from automobile frames to commercial aircraft winglets.

 

Can anyone give me an answer as to what is going on?

[studiot]

Fibre reinforced composites are relatively new materials and many users do not understand them properly.

 

So inappropriate manufacturing design is applied.

 

This can be in several forms.

 

a) Physical

Inappropriate stress concentrations.

Inappropriate shear transfer devices

 

b)Chemical

Insufficiently clean and dry manufacturing conditions leading to premature chemical degradation.

 

Check out 'osmosis' in grp boat hulls.

http://www.anchormarinesurveys.co.uk/osmosis.php

 

Excessive material thicknesses causing internal overheating during curing.

[StringJunky]

In fishing rods, they lose their recovery rate - springiness - over time, which is the rate at which it returns after being bent; it affects casting performance. There is a process by which premium rod blanks are put under, but the term escapes me atm. that preserves the recovery rate for longer. In a nutshell, over time, the rod bends more under less load and you can't cast as far. UV and air are the culprits IIRC. If I hit on the right term I'll know fair bit more that I can post on the phenomenon. Savvy anglers are finely tuned the performance of their rods and can feel when they are failing.

[RiceAWay]

In fishing rods, they lose their recovery rate - springiness - over time, which is the rate at which it returns after being bent; it affects casting performance. There is a process by which premium rod blanks are put under, but the term escapes me atm. that preserves the recovery rate for longer. In a nutshell, over time, the rod bends more under less load and you can't cast as far. UV and air are the culprits IIRC. If I hit on the right term I'll know fair bit more that I can post on the phenomenon. Savvy anglers are finely tuned the performance of their rods and can feel when they are failing.

 

High end bicycle frames and forks are seldom allowed enough exposure to UV and they are constructed so that they do not flex. So plainly this is not the problem.

 

A couple of manufacturers have insisted that the MAXIMUM amount of "safe" time that these frames and forks can be trusted is two years. Now from experience I know that this is more like 15 years but these manufacturers are protecting themselves from lawsuits.

 

However, there have been these failures that suggest that what is going on is that the bonding of the resin to the reinforcing is changing over time. I can't find it now but I did read an study that suggested that cross bonding continued over time changing the nature of the resin.