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  1. #26
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    Quote Originally Posted by Jay Strongbow View Post
    That begs the question: Why wouldn't crashing a race bike be considered "normal use"? Not exactly far fetched.

    If it can be made to resist impact why isn't it? I always figured it was for weight weenie reasons and they thinned out the tubes to look good on the scales. But from what I gather of what you're saying not making them impact resistant is due to stupidity (well, I consider it stupid to not think crashing is 'normal' for a racing bicycle)

    As per my example of hockey sticks I think you definitely right that it could be designed to resist impact, so why not?
    In order to "resist" impact with a laminate material like carbon fiber, you're going to need a lot of it. Yes, weight is driving much of the design. So they're not going to build a road bike to be able to "resist" impacts.

    What they are doing is basically making them like they make safety glass now.

    They are sandwiching in a layer of polyethylene in the middle of the layers, just like how safety glass is made. This high modulus polyethylene fabric they're using is called Dyneema.

    Not going to stop the material from breaking, but it'll hold it together after it breaks.

    It's something I guess.
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  2. #27
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    Quote Originally Posted by aclinjury View Post
    This test would have been more valid if they had scanned each frame (aluminum and carbon) for internal damage after each iteration. That means they needed to use ultrasound and x-ray, if they wanted their experiment to be robust.
    You don't "scan" metal for damage because what you see is what you get - there aren't any hidden layers. In aviation crack inspections for aluminum wings are done with dyes that make cracks obvious. Not cracked = not cracked. With carbon wings you have to xray them to see delaminations that might not show on the surface layer of carbon.


    All hockey stick stuff goes back to the "beer can principle" - if the tubing wall is too thin, the structure will not survive minor bangs even though the overall structure is strong enough for the job. Steel bikes could be two pounds, but the tube wall thicknesses would be like foil. Hockey sticks in carbon are durable because the "wall thickness" is great enough that there is no where for the laminations to collapse into, so they don't dent.

    This is the reason I have a Calfee Luna. It has the nice riding properties of a good carbon frame, but the lower diameter tubes have rather thick walls making them harder to damage. The price I pay is a little weight - and since I'm not a pro and plan on keeping my bikes, a little weight is worth it to me.
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  3. #28
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    Quote Originally Posted by Kontact View Post
    You don't "scan" metal for damage because what you see is what you get - there aren't any hidden layers. In aviation crack inspections for aluminum wings are done with dyes that make cracks obvious. Not cracked = not cracked. With carbon wings you have to xray them to see delaminations that might not show on the surface layer of carbon.
    Dye penetrant is for surface cracks only. Things like eddy current and ultrasound (a 'scanning' process so to speak) are deployed with metals to find interior or non-surface defects and irregularities.
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  4. #29
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    Quote Originally Posted by craiger_ny View Post
    Dye penetrant is for surface cracks only. Things like eddy current and ultrasound (a 'scanning' process so to speak) are deployed with metals to find interior or non-surface defects and irregularities.
    That's true, but my comments were bicycle specific. You aren't going to have "interior" failures with a structure made of single layer metal tubes.
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  5. #30
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    Quote Originally Posted by Kontact View Post
    That's true, but my comments were bicycle specific. You aren't going to have "interior" failures with a structure made of single layer metal tubes.
    Probably not and any crack I have to believe is likely going to be through given the thickness. I have seen interior cracks in tubing but no where as thin as bicycle tubing. The most common anomalies I have ran into are thickness variation but again I have not worked with bicycle tubing.
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