I hate, hate, hate the anti-scientific view that busted carbon promotes.
Carbon fiber's failure mode is different to metal - it breaks rather than bends. In most cases crashes that destroyed carbon frames would have also destroyed metal frames - but a frame bent out of alignment doesn't look as spectacular.
It is possible to build a bike from carbon fiber that fails in surprising ways (eg, clamping it in a bike carrier). That's because CF allows more flexibility in building with it, not because it is inherently weak.
If you want a strong carbon frame buy a cheap one. They typically use the same number of layer of fiber all over the frame (instead of trying to minimize weight in low strain parts) and they use plain woven fiber aligned randomly. That makes the bike heavier than a high-end frame, and not as strong for expected stresses (pedalling) as it could be for the same weight but it makes it more robust in the even on unexpected strains.
I hate, hate, hate the anti-scientific view that busted carbon promotes
WAT? Are you a materials engineer? Its CRP - carbon reinforce PLASTIC. The resin is prone to degradation from fatigue cycles. Raw carbon fiber without resin is brittle, think pencil leads. Bike racers (not sponsered) commonly race aluminum frame because a single "drop" if it doesn't render the fram unusable from catastrophic damage, can render it structurally unsound. That's the nature of carbon fiber. If my CF (CRP) motorcycle helmet so much as drops on the ground, it has to be X-rayed by by SHOEI to test for unseen damage that would render it unfit to work in an accident.
Strength is misleading for a material that is not tough. Steel frames and Titanium frames are far tougher than CF/CRP frames, they can survive crashes without catastrophic failure. Even the Pro-peleton used ALU drop bars for many years for two reasons (1) they bend, dont break in a crash; (2) CF bars don't reveal potentially catastrophic failure to the naked eye (like the moto Helmet example), so even A minor drop (if it looks ok and you keep going) is now a huge risk factor (when racing in close quarters - you bars break, you can take out alot of people).
Edit:
If you need more "scientific" evidence, for any reason, use Google compare shear/failure points of epoxy resin (vs steel vs titanium vs Alu etc). Yes you can overbuild anything, but you need to understand the materials you are working with. And also, as those pictures show, in the REAL WORLD the stuff that is for sale BREAKS.
Yes, people get injured when they have bike crashes.
Yes (as I noted), carbon can fail. Metal can too! [1] is a much better survey of random broken bikes than bustedcarbon. [2] is a good summary of the hysteria around breaking carbon frames and some of the facts.
I guess one point is that carbon fails catastrophically more often, your metal links
point to breaks where the bike still stayed in one piece. Yeah, they're not unheard of with metal bikes, but much more rare.
The injury quote was about her getting injured because the
carbon frame just fell apart with no warning (no crash,
except after the frame failure of course).
I guess one point is that carbon fails catastrophically more often
- There are "scientific" reasons why these things break for no apparent reason. b/c carbon is prone to developing "flaws", not all of which are visible (to naked eye). These happen either through previous impact damage or fatigue cycles.
- Carbon failure can cascade (snap...snap...snap...). Once the structure is compromised, the lack of sheer strength combined with different-from-design force vectors...are not good (a two-sided trianle = wishbone...) Look at how many carbon parts had multiple, complete failures.
- A metal frame will dent or bend if damaged; it doesn't hide flaws nearly to the same extent. You might get a hairline crack, but unlikely 3-4 snapped cross-sections.
-Obviously, getting hit by a truck or whatever doen't matter what you are riding.
These are directinally correct for raw materials; the actual alloys and engineered structures will take into account obvious characteristics of the material.
I would recommend anyone thinking carbon fiber makes stronger bikes to visit a topical image blog at http://www.bustedcarbon.com/ :)
The weight issue is addressed elsewhere in comments...