His composite racing bike handlebars BROKE in TWO pieces

I'm fully ready for the mech' eng' guys to slate me on this...but my view is it is typical crass design.
All the strain will go right back to where bars are clamped...the design should have the wall thickening as it goes from the end to the clamp point...or to put it another way, it should effectively be tapered so that the stress is distributed along the length of the bar in an even manner rather than concentrated at one point. Thats why a longbow is tapered... don't we all learn that as kids? Ok it's difficult to make a metal tube of tapered wall thickness...but a composite would lend itself to some proper clever design.

Of course on a regular bike they just over engineer these parts so there is little flexing or chance of a break.... designing light weight stuff requires a little more subtlety.

Fire away guys, I've got my kevlar suit on

Del

Fire away guys, I've got my kevlar suit on

Running short on lives or is that just your winter coat?

to follow up on DellTC has said here: i generally find that the higher modulus materials tend to be a whole lot more sensitive to design principals. i.e. notch sensitivity, & other methods of applying loads

Not that I am much of a fan of them, but this seems more like a job for an attorney.

Your point is well made and the attorney is already sucking up a lot of fees as his 'expert' consultant.

I do a lot of fishing and have noticed over the years just about all the composite rods I have had that broke were due to scratches on the tube. The scratch greatly reduce the amount of force that can be placed on the rod before it breaks.

Yep,

The scratch acts as a stress concentrator; a small, sharp bottomed crack can result in a concentration factor as high as ten, and unless the material can plastically deform to blunt the tip of the crack, its going all the way through in a real hurry. The way the bar itself is clamped could be the cause if the scratch.

Glad its not my design......

But, Folks, as a tubular design, isn't this an application where continuous fiber strands wrapped around the product would prevent a crack from going right through the handle bar and causing a fracture?

Fuel and Chemical Storage tanks are made in such a fashion! Is it too expensive to produce a product with continuous fiber? Or, is this just a poor design where chopped fibers or fiber patches (if that's a good term) are used.

Hi Walter,

Without seeing it all we can do is speculate. The best way to do it (IMHO) is to use continuous fibres that run from the left hand grip all the way to the right hand grip in a design that (as Del said) should be tapered to have its widest section in the middle, with suitable extra re-enforcement and surface protection. This is also the most expensive way to do it.

It could be that the composite tube was extruded and cut to length. In this case they probably mixed (very) short fibres into a matrix, which will have considerably less strength. Also, the fibre to resin ratio will have a big effect on the strength, as in most composites, the strength is all in the fibres, not the matrix. Its also important that the type of fibre, and their lengths, are appropriate for the resin used, as the usual failure method for composites is tear out of the fibres from the matrix material. If the fibres are too short, if there are not enough of them, or if they simply do not bond well to the matrix, the strength of the component will be severely compromised.

It could just be that the designer of the handlebars failed to take into account the forces involved when considering shock loading, fatigue and surface defects.

But, as I said at the beginning, without examining the parts, its merely speculation.

Slightly off topic, with steels, as you increase the strength, the ductility decreases. If you have a weak piece of steel, it will deform greatly before it finally fails, giving plenty of warning that there is a problem. A high strength steel will resist much more force without deformation, but when it fails, it will usually be catastrophic, with little if any warning that there is a problem.

The art of good design is to select a material that is strong enough for the job it needs to do, but not so strong that it won't give you a visual indication (such as a permanent bend) of being overstressed BEFORE it breaks.

I am just guessing in this, but i'd believe that it might be a "pull-trusion" where the fibers are all parallel to the axis of tube(unidirectional reinforcement). Easy way to make tube stiff in bending, tho, maybe not quite so resistant to buckling.

"The way the bar itself is clamped could be the cause"

Even if the clamp did not produce an actual notch, there would be a large change of stress at the boundary of clamp/air (providing the clamp is gripping the bar).

I will, on occasion use an elastomer sleeve inside the clamp to reduce the stress at the clamp ends. Much easier fabrication than variable tubing.

What give carbon fiber its strength is that the fibers are laminated in different directions.

Each direction it would only have strength in only one axis.

With the information listed, it looks like a design problem or lack of design when specifing the amount of laminations.

Hello Walter Mitty

The big problem with Carbon Fibre items is abrasive damage.

Like glass, metals and other materials, a tiny scratch is enough to start the stress propagational crack, that in some cases happens so quickly it is catastrophic.

While there is not much damage in case of a broken fishing rod, a cycle, tank or other item which may endanger the user is suddenly cracking, is better not to be made of Carbon Fibre.

I have seen an expensive Carbon Fibre cycle frame broken, the cause being a few turns of the pedal, as the chain dragged across a frame tube.

I suggest if you do need a very strong and light cycle, best at this time to get one made of Titanium, which is expensive to fabricate.

But at least the cycle will survive, along with the rider.

There is a very informative webpage here: http://www.sheldonbrown.com/frame-materials.html

Kind Regards....

Hey Guys,

I am a sailor and often we use laminated masts and other parts. We know we have to rinse them afterworths extremely wel every time or the mast or other parts will de-lamminate and lose there structural strenght . Only water right PH clean etc will do the job.

Sugestion: examin the other handle.

Sorry for my English but I try to help on the topic.

PvW

Good morning all,

Walter, this sounds like a horrific accident, my (I guess our) best wishes to your friend for a full and speedy recovery.

I agree with all the comments on the board so far (tapering, the consequence of scratches in composites, etc.)

It's an accident scenario I've been paranoid about since beginning to ride bicycles as a little kid. (I often tend to start warily glancing at the ends of the steering fork on a fast downhill run, thinking about the spaghetti bolognese I would become should THAT part of the frameset fail...) My road bike happens to have a carbon fork which you can bet I'm now going to inspect with a 3D microscope!

Well I for one would like to know the brand of this bike! I mean, you haven't given the details of the accident, but this failure could well have resulted in the rider's death. It's not the first time I've heard of bike component failure (esp at the high/lightweight end), but I think it's the first time I've heard of handlebar failure. What a nightmare.

Best Regards

RF_G

Another point...If I were building/fitting such bars I'd fill 'em with expaned PU foam (to help reduce flexing) and also be sure to tape 'em up at the clamp point (if not all over) to avoid the scratches ...were they fitted according to manufacturers recomendations?

Del

Has anyone tried to contact other bike owners using the same handlebars? Precautionary measure, as opposed to gathering evidence (which may be a welcome side effect).

With these bikes, the intention is to reduce weight as much as possible. That's why they switched to carbon fibre in the first place. The problem is that the manufacturer has sacrificed strength for weight.

With carbon fibre, my experience is that failures are always catastrophic with very little indication before hand that the failure is about to occur. If this handle bar had been constructed of steel you would probably had deformation just before the failure.

I believe that if you purchase one of these bikes you should be made aware that failures may occur without warning.

That is a pretty poor philosophy...and a cop out .
OK they are after reduced weight...but shouldn't sacrifice strength*... if it's being used for racing the stresses will be higher than normal.

Bottom line is it should be fit for purpose ... it wasn't (unless of course it wasn't fitted/used in line with manufaturers instructions*)

* The exception would be if it was designed to be replaced at frequent intervals.

Yeah it is a cop out. But you know as well that people sacrifice a lot to win.

I would say, they should go back to more proven materials, until they can come up with a composite that will hold up.

Yes there are compromises one has to do. But when safety is an issue, that is a hard sell.

Funny you should mention sacrificing weight for strength. Apparently, that's exactly what Airbus did on their A300 before the tail broke off over Queens NY killing 260 folks back in 2001. I believe the composite tail broke off due to "excessive" flight control input. I'll be damned if I'll fly on one any more than I'd fly on a DC-10..

I saw a program recently that showed exactly that failure. It was down to a bad training technique taught to some pilots and the fact that the stabilizer had too much control movement, more than would ever be needed.....

The pilot literally broke the stabilizer off by using full left-right-left-right, not once, but 3 times I believe......just because he was flying in the turbulence of another aircraft!!! The Guy had no feeling for the machinery at all......

If its any conciliation, the simulator training has been long ago corrected and the stabilizer cannot go so far left and right anymore!!!

Personally I still fly Airbus very happily as they have had very few bad accidents to my mind..... and the computer systems they use have actually saved lives when pilots have done stupid things. They have had their problems, but the batting averages are good.....

I never fly on DC aircraft, no matter what you would pay me.....

Boeing are relatively OK, at least since they fixed the overheating of the fuel tank from the air conditioner and rewired AROUND the tanks (747)!!! Also, having fire sensors cross wired on 737s, which caused pilots to shut the good engine down when a fire started.....you only have two!! Fuselages on older aircraft falling apart in flight to Hawaii (737 again).

Look what the first British jet airliner went through for crashes (the Comet) in the 50s......ouch!!!

The BAC111 in the 70's that went down near Heathrow when the pilots coffee cup fell over and doused the three computers in a blind fog takeoff......etc etc etc you could go on for ever.

I was on a Comet that lost the nose wheel when landing on Gan in 1966.....after repairs (3 days) we took off and had to pump the undercarriage down by hand to land in Bahrain....hydraulic fluid was dirty!! 4 days wait!! Over a week to get home from Singapore care of RAF.....but we got there in the end!!

I was on a Lufthansa 737 at Frankfurt 3 years ago that blew an engine up as the pilots fired up to take off!! Also I was on another small plane of Lufthansa 3 years ago that had to do an emergency stop in the middle of taking off because of a lack of oil pressure to one engine in Gothenberg, Sweden.

Then the RAF transport plane (US built) where we tried to take off over 10 times before we made it without a red light coming on in 1967!!! Very nervy!!!

I have been through turbulence when legs have got broken because the passengers were not strapped in and the plane fell a long way, I do not know how far, Singapore 1965 Boeing 707.....4 hours of a flight from Boston where even the passenger crew had to stay strapped in their seats, very bad for the Sphincter muscles......

Plus others. I still fly though!!! As do many other people with even worse experiences than I have had!!!!

Each must make his own choices in such matters with whom he flies......

Hello Andy , as usual you have hit the spike squarely on the head.

the big problem that is not so much a flaw in the design of the device but in the user the device is designed for. the resins as sparstation points out are a problem the fibers have to be in perfect chemical agreement with it. not keeping the surface free of scratches on a propylene glycol storage tank made with carbonized fibres will really allow less than hairline cracks to start then they spread out all over the sides and bottom of the tank. when that happens all it takes is a touch with a bung wrench to shatter the side when the unit has been in the process line about six months.

Andy,

I would definitely fly with you! Anyone that has survived so many aircraft quirks as you have is amazing.

Oh yes, I did fly a DC-10 shortly after the crash in Cerritos California. I have never been afraid to fly. It's not the aircraft but the PEOPLE piloting and maintaining the aircraft that worry me. I.E. Germanwings Flight 9525

Walter Dear,

Immaterial how this man-made composite was made. After all ,it failed - did it not?

I can send you the real stuff--Nature's very own--will last and last--BAMBOO!

Just send me the OD,Length,mass(max) and your post+Telephone #-- and wait 3-4 days. If you must have the grips in fancy curves-- I shall form them too. But how is the fitting? Inserting or clamp-on.

If you can send photo with a scale held next--we will know a lot better--how to....

Everyone that has talked about stress concentration, scratches, and abrasion are right.

I don't think anyone has talked about improper layout - if the fiber was not wrapped or formed correctly, a natural break point could easily have been made. The wrong type or amount of resin could have been used, it might not have been vacuum formed correctly, cured at the wrong temperature, etc., etc., etc.

The lawyer should have the other side of the handlebar and the broken piece inspected by an engineer that works with composites. The manufacturer's inspection and training practices should be examined. The shop that put the bike together should be examined too - they might have sanded down or otherwise modified the parts in a detrimental way without understanding the consequences.

Even with sacrificing strength for weight, this type of composite part usually still has a high factor of safety. I would believe a manufacturing error before catastrophic design flaw - this doesn't happen with every carbon fiber handlebar...

Best wishes to your friend.

I agree with all comments so far.

Clamp is likely source of problem. Get copy of assembly instructions for handlebars and then depose the mechanic, (lawyer stuff).

get another copy and test yourself (stress, scratch, stress, clamp too hard, stress)

I'll end with some advice I got a long time ago on ultra-light bicycles...

"save your money and skip breakfast the day before if you want a bike that is 1 pound lighter"

The point as I understood it is: we spend way too much on making the bike lighter when the vast majority of the weight is the rider. Only in extreme cases will it make any appreciable difference in performance. It is usually just a status/envy exercise.

http://cr4.globalspec.com/comment/159641

I HAVE READ ALL POSTS THROUGH #24...

1. Being an application engineer by habit...I ask "where did the excess load on the handle bars come from" that induced break?

Did rider have the habit of excessively leaning forward on the handle bars on down hill runs...[off seat] TRANSFERING SUBSTANTIAL BODY WEIGHT ONTO BARS..... beyond average/normal? Thereby overloading the original bar/weight calculations?

Steering load, as designed, should not have to consider anything beyond 400% of the steering force required. Steering a bike should not need more than two finger/thumb on each hand....my opinion.....of course I am many years beyond "bike" memory at 82.....though my sister used to ride on the handle bars over country roads....

2. Where did the "scratches" come from?

Abrasive cleaning compounds used to clean bar surfaces? This breaks the surface tension on the composite.

Transiting fastening system for taking bike to "location" [on top of the car] ..clamped...tie down for wind resistance at hi-way speeds?...visual appeal "enhancements after manufacture ...by owner..ie: paint..tape...striping for new looks?

Excess re-clamping tightening re-installation of bars after transit of replaced removed handle bars for said transit? [a common practice in my observation].../no torque wrenches in sight.

Many exposure posibilities.......no answers without considering the aboves and many more.

I am not trying to assign blame...or relieve blame...there is enough to fit everyone. Having no ability to "hands on", I postulate.

MR. GUY

1. Being an application engineer by habit...I ask "where did the excess load on the handle bars come from" that induced break?

When designing you MUST design above unity with a margin of safety. I do not think because the rider lean forward should constitute excess load

Well said...also.. a ride standing on the pedals to go uphill will pull up hard on the bars. Impact load on crashing should also be considered.
Maybe that's why so many riders go no-hands? To avoid stressing the bars...

Look Ma no-hands..
Look Ma no teeth...

Del

as one bike enthuisist says to another.

yes thats my bike hanging on the wall, I can lift it with my little finger. I payed $7,500.00 for it.

wow, says the second enthusist, you must do alot of biking with it.

no, I just look at it cuz, I'm afraid if I use it I might break it.

Nice comment! As someone in the industry, what is your opinion of using carbon fibre? I have felt for a long while now that it's a fashion statement, and is not practical for the everyday cyclist!

PlbMak,

My view is that a carbon fiber design is only so good as the designer, manufacturing expertise and user discretion. Moreover, only the user can decide what his real purpose is and whether he really needs a carbon fiber bike or not (do you need CF for commuting 4 miles to the grocery, you know stuff like that).

Carbon fiber is unbeatable in its properties for racing bikes compared to conventional materials. If designed improperly, it can also injure people and take lives.

A good example that comes to my mind is the tail fin failure of the Airbus A300 (American Airlines 587 I believe) shortly after Sept 11.

If you go to a section in my blog here, I have collected some carbon fiber failures on bicycles. I like to study them. Which is why I asked for a picture from the original author of the post regarding his friend's handlebar.

Mornin' PB,

another good entry, thanks.

"Which is why I asked for a picture from the original author of the post regarding his friend's handlebar." - I advise you to write directly to him (Waltermitty) because there's a good chance he's no longer monitoring this thread. In my (short) experience, the half-life of CR4 discussions is about 6 hours, with the great majority going dead by the next business day. This is one I hope continues because I like biking (I have 4, and here in Switzerland, where a significant number of people don't own cars, it's taken seriously, esp commuting) and it touches on a lot of different aspects of engineering ('wholistic' design, engineering ethics, appropriate choice of materials/technology for a particular application, and so on).

Best Regards,

RF_G