Originally Posted by
maartendc
Lol, I see an impact test and a fatigue test, and I see what impact and fatigue resistance the materials have. How does that not prove anything?
As a matter of fact, I do have an engineering degree in construction engineering, because you brought it up. I took a materials science class or two during my studies, including some lab experience with carbon fiber. I won't profess to being an expert on carbon fiber though. In my college lab, this is how impact resistance of materials was tested, exactly as shown in those lab tests in the videos. I don't see anything wrong with their methodology.
It doesn't. That was my point, they are different materials, they fail differently, have different properties. Both are good materials if designed with properly.
The polymer resin is supposed to "harden" during manufacturing lol, that is what the resin does. Do you mean it gets more
brittle over time? I have never heard of this concurring. Do you have some studies to back up that bold claim? I believe resin is very brittle to begin with, but since CFRP is a composite material, you cannot look at the properties of any one component, but rather the whole composite. The fact that you refer to the resin as "hardening" versus "becoming brittle" seriously makes me doubt you have a materials science engineering degree.
In the case of the Colnago C40: They used carbon lugs bonded to carbon tubes on those models. The failure seems to have occurred where the lugs were bonded to the tubes. Perhaps in those early C40 models (manufactured from 1993 onwards) they got something wrong with the bonding of the tubes to the lugs? You cannot really compare this to a monocoque frame (made out of a single piece).
Again, I would love to see some actual scientific study or paper showing that the resin in the carbon fiber becomes more brittle over time. Have never heard of this, but I would be genuinely interested.
By the way: if you are an engineer for Lockheed, you surely know that the new F-35 fighter jet, made by Lockheed Martin, is using a lot of CFRC in its body. I suggest you never test fly one if you are so concerned.
https://www.compositesworld.com/arti...e-f-35-fighter
Or never get into a Airbus A350, which uses 52% CFRF in it's body:
https://en.wikipedia.org/wiki/Airbus_A350_XWB
As a construction engineer I would expect you to be more knowledgeable about resins than that. Resin never really cures completely and continues to harden over their lifetime. Progressively slower and slower of course but at the same time the resin grows more and more brittle and is degraded by UV light. This hardening in the older bikes didn't much matter because they were so overbuilt that even the resin hardened almost to glass hardness was stronger than any expected load on these bikes. But the new bikes are not built for strength, they are built for ultimate lightness. Several people have bragged that DuraAce equipped bikes with DuraAce wheels (not the lightest around) are under 12 lbs. My brothers 10 year old Giant TCR-0 weighs 16 lbs. Giant well knew how to build lighter bikes then but didn't. Now you ain't got a bike unless it's well under 16 lbs.
The test of aluminum frames and carbon fiber frames when the strength of the CF is at it's highest expected lifetime strength is hardly an accurate test don't you think? Colnago has some of the best CF engineers on the planet and they give a 3 year warranty on their C60 - what, a $20,000 bike with a complete group and reputable wheels for a bike that expensive?
Why would you expect a company that is supposed to be one of the best on the planet to offer a warranty that short? Because they think they might get sued? Doesn't work that way. They're an Italian company and there aren't laws that allow that sort of thing. What's more, if they were that worried about it they could simply close their US distributors and be proof against that sort of thing.
When these CF bikes are first completed they have their resins something like 92% cured under heat and they are at the point where they have the highest strength while having the greatest flexibility of the resins so that it is proof against brittleness.
And if you read my treatise above you would see why they can get away with using CF in the F-35. Would you expect a supersonic aircraft to be built for lightness or strength? What's more there is a "useful lifetime" for a fighter. And I would love to see what it is expected to be for the F-35. Aluminum fighters are lined up by the mile in the desert storage yards in the sun. B52D's that I worked and occasionally flew on in the Vietnam War are still sitting on the pad at March AFB and they could still call me up to work on them. That model first flew in 1954. I will guarantee you that any fighter with CF parts will replace them on a timely basis. The Buff-D would need fuel. And I could design a new bomb/nav system the size of a PC and a Laser radar 10 times more accurate instead of almost half of the total electronics on the aircraft and weighing perhaps a ton.
Anyway try looking at
https://www.google.com/search?q=carb...7vwIxNcvhCn1M:
Many of these failures were from crashes. They were crashes that any aluminum frame would have lived through with little damage but I think it's still unfair to count crashes as a CF failure. But plenty of them were just plain failures for no reason whatsoever. And in the TdF I saw one of them occur near the back of the pack. On the flats is where the climbers congregate and they have special very light bikes built for them.
Remember that these bikes for the grand tours are built just shortly before the races and they are at their peak strength.
So those tests on Santa Cruz frames are unreliable because besides being on new frames that are at maximum strength the forces are applied slowly and smoothly. A crash is liable to give full loads in milliseconds when an aluminum frame would generally flex and bounce back. Putting a load like that over such a long period of time is not a good test of the strength of the frame material.
I didn't say I was an engineer at Lockheed. I said that I am on their list for projects in the SF bay area and I suppose they don't have any right now. Since I got that initial contact I figured it was a spam and didn't answer it. But I got a second "please respond" and tracked it back to Lockheed Grumman so I know it's the real thing. At one of the companies I worked for I designed and programmed boards used in the International Space Station which at that time was only three modules. Now I think that it's more like 15. Elon Musk says he's going to expand that.