Part Failure: 3D Printed Titanium Handlebar at the Tokyo Olympics
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    Default Part Failure: 3D Printed Titanium Handlebar at the Tokyo Olympics

    A rider on Australia's track cycling team suffered a crash in the Team Pursuit at the Tokyo Olympics when his 3D printed titanium handlebars snapped.

    Luckily for his three teammates, he had just finished his pull on the front and was riding 4th wheel when he crashed. Had the bars snapped earlier, he would've taken out the entire team.

    More here:

    https://youtu.be/EF-pgfgahbI?t=56

    Australia's snapped handlebar 3D printed, since removed from sale, reports claim | Cyclingnews

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    Surely....that's fatigue then?

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    I'm sure someone much smarter than me can answer this.

    What does the grain structure of a 3D printed part look like? How does it compare to cast/forged/drawn material?

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    It looks like pumice,and has tensile strength equal to blackboard chalk.

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    Quote Originally Posted by Camputer View Post
    I'm sure someone much smarter than me can answer this.

    What does the grain structure of a 3D printed part look like? How does it compare to cast/forged/drawn material?
    Done correctly, it's slightly better than bar or plate stock. At my last job we had titanium parts 3D printed by LayerWise in Belgium, and along with the parts we had a bunch of tensile test coupons printed. The printed material had tensile strength results slightly higher than material cut from plate stock.

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    Quote Originally Posted by charlie gary View Post
    Done correctly, it's slightly better than bar or plate stock. At my last job we had titanium parts 3D printed by LayerWise in Belgium, and along with the parts we had a bunch of tensile test coupons printed. The printed material had tensile strength results slightly higher than material cut from plate stock.
    Perhaps because it was harder than the wrought ti. Exposure to a small amount of oxygen can increase the strength of Ti, but at the expense of ductility. So the printed parts may have gotten some excess O2 exposure, but may have wound up a little brittle?

    Origin of dramatic oxygen solute strengthening effect in titanium | Science

    High oxygen-content titanium and titanium alloys made from powder - ScienceDirect

    Darn glad that rider wasn't hurt significantly. Could have been a lot worse...

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    Quote Originally Posted by john.k View Post
    It looks like pumice,and has tensile strength equal to blackboard chalk.
    oh hello, ignorant comment of the day.

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    Famous Aussie sailing saying would fit well in this situation
    “If it doesn’t break it’s too heavy”

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    Quote Originally Posted by barbter View Post
    Surely....that's fatigue then?
    Probably crack propagation starting with a small internal defect, and possibly embrittlement during sintering.

    Solid titanium bars and forgings usually start from a cast billet that's vacuum arc remelted multiple times to eliminate internal defects.

    With 3D printing, you have no idea what's inside. NDT is difficult, if not impossible, to perform on a finished, hollow part with lots of curved surfaces.

    For mission critical titanium parts that require high structural integrity, ultrasonic NDT is done on the raw material due to its uniform shape, e.g. a round bar or disc. The resolution of the scan is limited to the surface roughness of the material, so you can't effectively scan a rough blank, but it's relatively easy and inexpensive to finish turn a simple cylindrical blank to a low RA prior to ultrasonic NDT. After NDT, the blank can be milled, and any potential external defects can be detected through mag particle inspection. Internal defects are unlikely to have been introduced during machining.

    I think titanium 3D printing still has its place, since the material is inert and has high heat resistance. More care needs to be taken for structural parts though.

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    Quote Originally Posted by Orange Vise View Post
    I think titanium 3D printing still has its place, since the material is inert and has high heat resistance. More care needs to be taken for structural parts though.
    My impression is that atmosphere control is very important with Ti printing, as the huge surface area of the Ti powder gives a lot of opportunity for undesirable O or N uptake if there's any leaks in the enclosure or poor gas mixture control.

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    It seems to me that the AMA banned aluminum handlebars on race bikes for this very reason years and years ago. Some parts you just don't want to take a risk on.

    Axles was another.

    p.s. why would they be running ti anyway ? If there's no rules against it, aluminum worked on 300 lb 120 mph flat trackers. Al is lighter, so why ti ?

    (Obviously the correct answer is not "because it doesn't break" )

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    The international cycling union, UCI, has specified 6.8 kilograms (15 pounds) as the minimum weight for a bike. Today, bike manufacturers can make bikes much lighter than that, so why is the rule still in effect when large parts of the cycling world would be happy to see it gone?

    Many of the ways that a bike rider can try to bend or break the rules that have been put in place by the UCI require advanced equipment to detect, but there is one that requires little more than a bathroom scale.

    Since 2000 the minimum weight for bikes used for competitions has been 6.8kg. In essence this means that if you show up ready to ride on something that weighs less, you’re not going to get past the race commissionaires.

    The weight rule has been a sore point for riders, teams and bike manufacturers for years. Although the rule was instigated to protect the riders, advances in technology mean that this protection is at best limited, while it in some cases might actually be lowered by the rule.

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    Quote Originally Posted by EmanuelGoldstein View Post
    It seems to me that the AMA banned aluminum handlebars on race bikes for this very reason years and years ago. Some parts you just don't want to take a risk on.

    Axles was another.

    p.s. why would they be running ti anyway ? If there's no rules against it, aluminum worked on 300 lb 120 mph flat trackers. Al is lighter, so why ti ?

    (Obviously the correct answer is not "because it doesn't break" )
    Every dirtbike has aluminum bars.

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    Quote Originally Posted by Milland View Post
    My impression is that atmosphere control is very important with Ti printing, as the huge surface area of the Ti powder gives a lot of opportunity for undesirable O or N uptake if there's any leaks in the enclosure or poor gas mixture control.
    Hydrogen embrittlement is a big deal too, from any moisture in the air.

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