Tern Link D8 frame shearing in two

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Tern Link D8 frame shearing in two

Post by Admin on Fri Apr 04, 2014 1:15 am

December 20, 2013 - 12:27pm
Lee Tibbetts

Joined: 2013-12-20
Country: UK



Hi all,
I'm wondering if any of you Tern owners have ever had or
come across a problem with the frame braking in two?
I'm just curious as this happened to me last Tuesday (10th Dec
(2013). The frame on my Link D8 snapped at the weld near the
folding hinge as I was traveling on a fairly busy London road at
night. I was fortunate in that the traffic missed me as I fell
but I hit my head pretty hard (yes, I was wearing a helmet)
which knocked me out. To cut a long story short, I had to have
a CT scan and several days off work with concussion (which I
still have the effects of a week after the incident).
At the moment, Evans are in contact with Tern about the
frame, but I have to say I'm now left with little confidence of
the bike frame. What if it happens again? Most people I have
spoken to (who are cyclist themselves) think that I'm pretty
lucky not to have come off worse than I did.... And I wonder
if you good selves have experienced anything like this and do
you have any advice?
I've emailed Tern myself but as yet have had no reply.
Just to be clear, I loved the bike... it was perfect for my
needs, purchased at the end of last February . I only used it to
commute between stations, a journey of 30 mins a day and I'm
below the maximum weight, so nothing that should cause such
a catastrophic failure to the frame.
Any ideas or advice would be most welcome. Smile
Cheers, Lee


edit: picture of frame failure.








Tern Link D8 frame Failure


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Re: Tern Link D8 frame shearing in two

Post by Admin on Fri Apr 04, 2014 1:16 am

December 20, 2013 - 12:48pm
bugaboosun


Joined: 2012-12-27
Country: USA

Whoa, I am sorry to hear about that. I hope your head heals
fast. As I own the same bike I am very curious about he exact
nature of the failure. Which particular weld failed?


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Re: Tern Link D8 frame shearing in two

Post by Admin on Fri Apr 04, 2014 1:17 am

December 20, 2013 - 1:07pm
Lee Tibbetts


Hey bugaboosu,

Yeah, I hope it heals fast too! I'm sure you'll be fine but it pays
to be curious.
It was where the folding hinge meets the front frame part.

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Re: Tern Link D8 frame shearing in two

Post by Admin on Fri Apr 04, 2014 1:18 am

December 20, 2013 - 2:08pm
thor





oh mei
not what I want to hear .... I hope you are doing better in no
time. The bike is a bike is a bike .. can be replaced, but
your well being is of so much more concern.

To answer your question, no I havent heard about a
catastrophic frame failure as of yet, You are the first.

Having said that I am sure that Tern will take care of you and
will get you a new frame. Being such a huge event for them as
well, I am sure that they would like to inspect the broken
frame and find out exactly what happened. Evans will most
likely be in contact with the Tern crew already.

All the very very best to you and Prayers and good Karma
from this side of the pond.
Thor
__________________
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Dahon: Freedom unfolds


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Re: Tern Link D8 frame shearing in two

Post by Admin on Fri Apr 04, 2014 1:18 am

December 22, 2013 - 9:46pm
amanda.uy
OFFLINE
TEAM TERN -
SERVICE


Hi Lee Tibbetts,
We’re sorry to learn about the accident. Evans has been in
touch base with us last weekend, and we’re going to request
to have the frame shipped back to us for further analysis.
Joined: 2011-11-22 I’ll let you know the findings once we have the frame at hand.
______
Sincerely,
Amanda Uy
Tern Bicycles | Service Department

Note: To receive the latest product information, please visit
ternbicycles.com/support/registration and register your bike.


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Re: Tern Link D8 frame shearing in two

Post by Admin on Fri Apr 04, 2014 1:19 am

December 22, 2013 - 11:17pm
Steveroot


Glad you had the helmet on and weren't hurt worse. It's easy
to forget that riding a bike has risks other than the "expected"
potential interactions with traffic. This particular failure
seems likely to be very rare, if not unique, but it would be
good to understand how it happened.

I would have liked to see some images of the joint. It's always
interesting to see how parts fail. It would be nice if the results
of the investigation were presented here.

Steve
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Re: Tern Link D8 frame shearing in two

Post by Admin on Fri Apr 04, 2014 1:22 am

December 23, 2013 - 5:18am
Lee Tibbetts


amanda.uy wrote:

Hi Lee Tibbetts, We’re sorry to learn about the
accident. Evans has been in touch base with us
last weekend, and we’re going to request to have
the frame shipped back to us for further analysis.
I’ll let you know the findings once we have the
frame at hand. Amanda


Many thanks Amanda, I look forward to your findings and my
bike, as I really do miss riding it.


Steveroot wrote:
Glad you had the helmet on and weren't hurt
worse. It's easy to forget that riding a bike has
risks other than the "expected" potential
interactions with traffic. This particular failure
seems likely to be very rare, if not unique, but it
would be good to understand how it happened.

I would have liked to see some images of the
joint. It's always interesting to see how parts
fail. It would be nice if the results of the
investigation were presented here.
Steve


Hi Steve, Yes, I wouldn't ride with out a helmet... I see SO
many cyclists out there riding with no helmet, it's their choice
but I rather like my brain! LOL! I've been riding for a good
number of years now and have to say it's the first frame
failure I've had. I'm used to the odd things that go wrong with
bikes, pedals going, etc and you just put that down to wear
and tear and experience.... but this was rather unexpected to
say the least and rather unwarranted. I really hope it is a one
off as I don't want people panicking as it's a really nice bike
and a nice ride.... however I still don't feel confident about
the frame, I suppose as accident is still fresh (well what I
remember about about it as I was knocked unconscious and cant remember some of what happened after my head hit the
road)

I'm not going to post any pictures of the frame yet until Tern
have seen and assessed the damage...


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Re: Tern Link D8 frame shearing in two

Post by Admin on Fri Apr 04, 2014 1:22 am

December 23, 2013 - 1:10pm
josh.hon


TEAM TERN

Hello Lee,
Very sorry to hear about your accident. I’m relieved that you
had a helmet on and are OK. We’ll look closely at your frame
to try and see what happened.
Josh


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Re: Tern Link D8 frame shearing in two

Post by Admin on Fri Apr 04, 2014 1:25 am

December 24, 2013 - 4:15pm
Steveroot



I'm not a welder or a metallurgist. From a little research, it's
apparent to me that good welding results, especially in
aluminum alloys, are dependent on a number of factors. Given
the low incidence of catastrophic failures such as yours, I feel
comfortable saying that Tern has a pretty good handle on the
welding proicess. I will resist the temptation to generalize
from my limited experience, which has been uneventful in the
weld department since I got my Verge and put over 1,200
miles on it. I had (what I consider) minor weld issues with my
prior folder, a Dahon MuXL.

For the interested, here are some links with interesting
information about welding defects. I was amazed by how
many ways a weld could be made poorly.Considering what I
said ^^ about the incidence of weld failures reported, there's
not much to worry about in a replacement frame IMO.

http://www.millerwelds.com/resources/articles/Common-
MIG-Weld-Defects-GMAW/

http://www.tech.plym.ac.uk/sme/strc201/wdefects.htm

http://en.wikipedia.org/wiki/Welding_defect

http://www.alcotec.com/us/en/education/knowledge/qa/How-
to-Avoid-Cracking-in-Aluminum-Alloys.cfm

Aluminum is a funny metal in some respects: it is light, which
makes it attractive for bike frames, but it's somewhat brittle,
which makes it susceptible to fatigue failure. Steel is better in
the fatigue-resistance area, but it's heavier so it's not as
popular for a frame material in bikes like folders where
lightness is favored. This thread prompted a walk down
memory lane for me, so here are some images of fatigue failures (not all in aluminum!) that I have experienced.

One thing that probably should be said is that most of these
problems with the metal developed over time. This might
have been the case with your frame latch, and it *might* have
been possible to see the crack developing before the joint
failed. I am *not* blaming you for not noticing. However, it
doesn't hurt to keep an eye on the welds on any bicycle. The
head tube of my Dahon Mu XL started developing a crack, or
so it seemed because dirt would collect there and couldn't be
wiped off. Eventually (after a year or more of watching) it was
obviously progressing. I had my brother-in-law re-weld it at his
machine shop. In spite of his warnings and disclaimers, it's
about 2 years since the repair and the crack has not
reappeared. The failure that nearly castrated me was the
Strida crank axle failure. The entire crank snapped off as I was
trying to accelerate through an intersection. By comparison,
the crank failure on my Dahon was more gradual... I noticed
that something didn't "feel right", and looked for the problem.
Same with the MKS pedal coupler.

So a certain amount of vigilance is a good thing, but your
particular problem is unlikely to recur.

Steve

EDIT: Notice on the axial view of the Strida crank axle that
some of the surface is rusty. This indicates the part of the axle
that was cracked for a time long enough for water (and
probably salt) to get in and corrode the metal. When there
wasn't enough of the axle left to support the torque load from
the motor (me), the remaining steel simply sheared off,
dumping me in the street.


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Re: Tern Link D8 frame shearing in two

Post by Admin on Fri Apr 04, 2014 1:26 am

January 27, 2014 - 6:52am
Re-tern


Country: UK

This has just happed to me too on a Link D8 purchased in
December 2012. I think from what you described my Link D8
snapped in the same place as yours, and like yourself I was
injured, but it could have been a lot worse if there was a car
passing me at the time. The frame snapped suddenly without
any warning whatsoever around the weld on the front part of
the frame where the folding hinge is attached resulting in me
coming off the bike and smashing my left hand on the floor
cutting and fracturing my index finger and heavily cutting abd
bruising my right elbow and right leg.This is a obviously a
serious flaw in the design of the Link D8 (or maybe Terns in
general) the frames appear to be constructed the same);
however when I contacted Tern I had no reply regaring this
issue (Evans cycles whom I purchaed the bike from have been
excellent though in dealing with this matter). I only ride the
bike on a daily commute of 12 miles a day on roads and paved
footpaths and only weigh 75kg, so there is no underlying
reason that this should happen. Previous to this I was pleased
with the way the bike rode; however in the year I have had it;
I have had to replace the pedals (6 months) th bottom braket
(8 months) and numerous spokes; additionally everything on the bike seemed to require tightening every few weeks as it
had become loose (seatpost / handlebars etc), even the Tern
badge on the front fell off after only two weeks. Most of all I
am disappointed that a new start company like Tern did not
even aknowledge myself or others regarding this issue; if it
were my company, I would try to do everything I could to
analyse the information and make good to create a successful
company who produce safe products. If you have a Link D8 9or
any Tern) I would be extremely worried about riding it as this
failure could be potentially fatal in a different situation, so be
warned! I have now done what I should have done in the first
place and purchased a Brompton.


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Re: Tern Link D8 frame shearing in two

Post by Admin on Fri Apr 04, 2014 1:26 am

January 27, 2014 - 11:35am
bugaboosun


That makes two. Now I am getting nervous.



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Re: Tern Link D8 frame shearing in two

Post by Admin on Fri Apr 04, 2014 1:27 am

January 27, 2014 - 11:35pm
amanda.uy


Hi Re-tern,

Apologies to hear the accident and that your e-mail to us was missed. We are contacting Evans to get your broken frame back. As of now, we’re getting our hands on both you and Lee Tibbetts’. We ‘re constantly following up with Evans on the logistics of the broken frames.

Amanda

TEAM TERN -
SERVICE


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Amanda Uy
Tern Bicycles | Service Department


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Re: Tern Link D8 frame shearing in two

Post by Admin on Fri Apr 04, 2014 1:28 am

January 28, 2014 - 12:25am
ng

Country: Singapore


Fatigue and fracture toughness should be examined. Or
contamination in the parent material. Or weaknesses due to
handling, welding and so on.

But all manufacturing processes should be checked for quality
to ensure safety.

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Re: Tern Link D8 frame shearing in two

Post by Admin on Fri Apr 04, 2014 1:29 am

January 28, 2014 - 7:54am
Lee Tibbetts


Hi mate,

Sorry to hear that you had the same issue as me!!!!! It IS
extremely worrying that it's now not just a isolated incident.
Even though you suffered some serious injuries, I'm SO glad
you haven't ended up worse.... as it could have so easily have
been!!!

Finally my concussion has gone (still had side effects from it
for 3 weeks!!). I had to go back to the doctors after the
swelling had gone down on my elbow... where they found that
I have smashed the cartilage of my elbow! But like I said...it
could have been SO much worse! But know I'm left with no
bike, no helmet (as the Doctors advised me to bin it as it's now
compromised, torn ruined clothes, smashed and floating
cartilage in my elbow!!!! Not good really on an ten month old,
well looked after NEW bike.

Just to let you all know, I've had an email from Mark (The Tern
UK Representative) on the 8th Jan (2014) saying that my Link
D8 has been requested to be sent back to the factory. I've had
no feedback or contact since then from either Tern or Evans.
(I'm guessing that Evans cant give me any info as they will be
waiting for Tern to supply it). So far Evans have been great....
but I do miss my bike. At the moment it's costing me a fortune
getting public transport!

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Re: Tern Link D8 frame shearing in two

Post by Admin on Fri Apr 04, 2014 1:29 am

January 28, 2014 - 10:45am
Re-tern




Hi Lee,

Sounds like you had a worse time of it than me to be honest,
at least i didn't hit my head hard. My bike is also a total write
off, as well as the broken frame, the crank impacted with the
floor so har that it has bent quite badly and also the rear
wheel appears to be bucked so badly it doesn't even rotate
freely with the rear brakes disconnected. I had no intention of
riding the bike again, as I don't trust it not happening again;
such a strange crash as it was completely unexpected. Evan
have taken my bike to send back to Tern and given me money
off a new Brompton that I purchased from them; being a steel
frame I trust that a lot more. I was only without a bike forjust
over a week, which was expensive enough, as well as several
hundred pounds out of pocket for a new bike too.

I have now had an email reply from tern, stating that they are
investigating the situation; I only hope that another frame
doesn't break on someone else whilst they are looking because
it could end up a whole lot worse. Let me know if you get any
feedback and I will also keep this post updated with any
response I get.

James


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Re: Tern Link D8 frame shearing in two

Post by Admin on Fri Apr 04, 2014 1:30 am

January 28, 2014 - 4:27pm
bugaboosun



Very regrettable incidents, to be sure.

Does anyone know how fast the cracks in these frames
propagated?

Right now, I do not see any cracks in my frame. Could a new
crack appear and propagate all the way through in one ride?
Or would a crack tend to gradually grow over a long period of
time?

How often should we inspect our frame joints?

What is the proper method for such inspection?


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Re: Tern Link D8 frame shearing in two

Post by Admin on Fri Apr 04, 2014 1:31 am


January 28, 2014 - 5:08pm
Steveroot

Country: USA


bugaboosun wrote:

Does anyone know how fast the cracks in these frames propagated?

Could a new crack appear and propagate all the way through in one ride? Or would a crack tend to gradually grow over a long period of time?

How often should we inspect our frame joints?

I am wondering the same things myself. Based on my experience with frame and component fractures on other bikes (2 Dahons and a Strida), I would speculate that the development of a fracture is a gradual process, at least initially. The sort of frank failures described previously would seem to be more likely after initial weakening by crack growth.

I had a seat tube fracture on a Dahon MuXL which took several months to completely circle the tube. I noticed it when it was about 25% of the way around. I opted to keep an eye on it, and eventually made a work-around (long story) which has enabled me to continue riding this bike safely (rode it today). I also noticed a crack across the top of the joint where the head tube joins the frame tube. I observed this crack for about 2 years before it began to propagate fast enough that I could notice it. I had it re-welded, and it has not reappeared for a year or more.

So my sense is that it is unlikely that the frame could fail "out of the blue". I'm not meaning to criticize either of the riders whose frames cracked, because this sort of problem isn't usually on anyone's radar screen. The other (important) question is: "how could these developing cracks be detected early?" On my Mu, the frame is natural aluminum. Cracks are easier to see because they tend to collect dirt and so look like dark lines on the metal. On a painted frame it might not be so easy. Still, if a structure the size of a frame joint had a crack developing around it, a very close inspection under good illumination should detect it. This would mean looking in exactly the right place, probably at the edge of a weld. For an entire weld to simply snap off instantly there would have had to be some systemic problem with the welding process, and I would expect this to show up in frame testing or very early in production, and I'd expect more than two reports.

I'm guessing that if such a crack were to start, it would be on the under-side of the frame, where I think the metal would be under more tensile stress. This would allow the crack to develop without being as easily noticed. How often should frames be inspected? I suppose the best time would be during routine maintenance or cleaning; that's when I noticed my cracks in the Mu frame. I noticed a crack in a crank because my foot felt funny on one side. I noticed a crack in a frame latch lever when it started feeling "soft" when I closed the latch. The only cracks that have taken me by surprise are the crank axle failure on my old Strida and the pedal coupler failure on my Mu (MKS removable pedals).

I'll certainly have another look at my frame latch when I take the Verge out of mothballs in the Spring. I hope we'll see some sort of report on this issue eventually.

Steve

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Re: Tern Link D8 frame shearing in two

Post by Admin on Fri Apr 04, 2014 1:32 am

January 29, 2014 - 1:48am

Keith C. Johns
Country: USA






First, my wishes that our two UK cyclist friends have no further encounters with bikes failing under them, and that their injuries heal fully.

Please read my posts in this thread:

http://www.ternbicycles.com/us/forum/tern-link-c7-vs-drhon-speed-d7

[Sorry, no way to link directly to the post on this forum; just scroll down until you see my name.]

While we must wait until Tern analyzes the frames in question, this sounds like cyclic metal fatigue to which aluminum is prone. This is why I no longer trust aluminum as a frame material, although I do trust it for components when built solidly for strength. With a life expectancy of only five years, quoted elsewhere, I do not consider the light weight of aluminum frames justification for such a shortened lifespan--I expect a quality bike to last a lifetime.

When I wrote the above posts, about a year ago, I knew that Tern Bicycles was too young a company to know for sure whether its policy of aluminum-only frames was best in the long run, since it would take time for their new frames to develop stress fractures in the aluminum.

Pending analysis, I want to again suggest to Josh that he consider at least one model with a titanium or chromoly steel frame material instead of aluminum. Because I sincerely wish for Tern to succeed, I hate to see them put all their eggs into one basket--their entire lineup in the aluminum frames. It is inevitable that more of these catastrophic failures will begin to appear over time, and that time is the only element which is keeping them at bay as of yet.

As Thor later stated to me, for the thousands of bikes Tern makes, there should be more reports of similar failures which simply are not there (yet). Is this because of the relative age of the company? I believe he was referencing Dahon's aluminum frames as well, which takes it back more years. Perhaps it is the periodicity of use of most of these bikes: if they spend more time folded in the cargo holds of RVs, planes and boats, they may not get enough use to ever show fatigue in most cases--but the ones which get used every day for commuting will certainly be among the first to reveal any flaws.

Steve is on the front line of regular commuter use, and has enough examples of aluminum frame failures, and steel components too! I just hope Steve never has a catastrophic failure in one of his aluminum frames where it comes without warning; but his careful maintenance will hopefully guard that flank. Good luck Steve!

The only thing which makes me pull back from totally condemning aluminum for frames is the fact that I have had some aluminum components like cranks and handlebars which should have failed, too, but never have over decades: Are these just more ruggedly constructed? The cranks are solid aluminum, not hollowed out to save weight. But the handlebars are hollow--perhaps thickly gauged for strength. And if the frames were similarly built for strength rather than ultra light weight, could they too become bullet proof? Herein lies the uncertainty: which is emphasized more on Tern's frames here: strength and durability, or light weight? There is where we will find the cause, for sure.

Staying tuned for more updates here, for sure.


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Re: Tern Link D8 frame shearing in two

Post by Admin on Fri Apr 04, 2014 1:35 am


Lee Tibbetts

Country: UK


bugaboosun wrote:

Does anyone know how fast the cracks in these frames propagated?

Right now, I do not see any cracks in my frame.  Could a new crack appear and propagate all the way through in one ride?  Or would a crack tend to gradually grow over a long period of time?

How often should we inspect our frame joints?

What is the proper method for such inspection?

What happened to my bike was sudden. I regularly clean my bike and I didn't see any cracks...at all.  maybe there was a production fault on the weld, as in my opinion, It seems a bit odd that the same thing happened to James and I, on the same model bike... in the same place (judging by James' profile pic). With mine, It's not the actual frame that broke but the weld that held both parts of the frame together.  All I can say is be very, very, VERY wary, wear a good helmet and lots of padding!!!

I'm going to go to Evans later on today to find out if they know any more on the situation of my bike as it's now been a over month since I dropped it in there.


Keith C. Johns wrote:

First, my wishes that our two UK cyclist friends have no further encounters with bikes failing under them, and that their injuries heal fully.

Thanks mate! Much appreciated! Smile They will in time.

Keith C. Johns wrote:

Steve is on the front line of regular commuter use, and has enough examples of aluminum frame failures, and steel components too! I just hope Steve never has a catastrophic failure in one of his aluminum frames where it comes without warning; but his careful maintenance will hopefully guard that flank. Good luck Steve!

I really hope NO ONE else suffers this type of catastrophic failure... I dread to think what would have happened to me just minutes before it did, there was LOTS of heavy traffic!



Depending on what Evans (and eventually Tern) say about the situation of the bike, I'll get round to posting the photos of the broken frame.

Lee

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Re: Tern Link D8 frame shearing in two

Post by Admin on Fri Apr 04, 2014 1:36 am


January 29, 2014 - 11:55am
thor



Country: USA


best of recovery to you two UK blokes out there. I understand your frustation, I guess number one got himself a Brommy, good on ya fella. Brommies are cool, however, despite their fanatic fan base ( and there is nothing wrong with that ) they have issues, frame defects are not unheard of either. Same is true for steel bike fridays or or or or  

I would hope that your dealer gets this into turbo overdrive and gives you a loaner, while the frame is investigated. It takes time to fly that stuff around the world and real testing and analizing the root of the defect is also time consuming. Or works something out with Tern to get you a new bike ( or frame ) or whatever.



Keith get over this alloy crap and metal fatique stuff you are constantly harping on. There were roughly 132 million bikes sold last year ... 90 % were alloy frames.That Number is pretty consisting over the last 10 or 20 ? years. IF alloy metal fatique would indeed be a problem, there would be thousands and hundred thousands of broken frames out there. Not so.  Steel is real ... comes from a clever advertising campaign. It has nothing to do with reality. When alloy frames hit the market some 30 years ago, it was indeed a problem with harsh ride or some frames breaking, that was 30 years ago. Even the bike industry as slow as it reacts sometimes, has learned a little bit.

In case of folding bikes, many many of them are alloy versus steel... lets talk about Dahon now, as I have some track record ( never had a broken Tern yet ) and guess what, despite that Dahon makes a lot of alloy framed bikes, I have more steel ones broken than alloys. Being the go-to guy in the US and sometimes worldwide, I receive an Ueber-Proportional amount of warranty or defective stuff..... in raw numbers, if I compare what I am selling its more steel breaks than alloy breaks.

Its also not real fair to take Steve frame into the mix, it was a prototype frame, he got for testing years and years ago, Steve is riding his bike today in minus temps, over salt encrusted roads, and everyday for years and lots of miles. He was offered a new production frame when the Proto was failing. Its great that Dahon and Tern pay very close attention to Steve as he is the "nightmare" user, and both companies are improving their products to make it work for "Steve". We all are benefitiing in the long run. ( Thanks Steve )

Sometimes stuff breaks, manufacturing processes are to blame, or miss use, or design faults, or simple mistakes while riding the bike. Hitting a pedal on a curb, can transmit enormous forces for example. Droping a folded bike during transport, can put undue stress on the folding mechanism. Sometimes the owner know about it, but write it off as "normal" use. Sometimes the owner doesnt know what happens ( air travel comes to mind )  Sometimes its miss use, the bike industry is full of stories : "Just riding along stories" are wellknown and "experienced" from bike mechanics on a daily basis.

I am not implying anything about the two cases we are reading about here. Just generalizing a very isolated incident is very wrong. I let my girlfriend, my daughter and myself use a Dahon or Tern alloy frame bike any day, without any fear that the frame breaks.  

Lets hope for a very fast recovery and also for a good end to this unfortunate incident

Thor


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Re: Tern Link D8 frame shearing in two

Post by Admin on Fri Apr 04, 2014 1:36 am


January 29, 2014 - 4:27pm
Steveroot

Country: USA



Thor, I LOL'd when I read that I'm a "nightmare user"! I think of myself more as just a "regular" user. wink

And I wouldn't have kept on riding the Mu if it was dangerous... it was only inconvenient as it turned out, and I hope the information I provided was useful. Obviously, the two frames in the UK would not have been rideable under any circumstances.

Don't be too hard on Keith. He has a somewhat different perspective on the metals used for bike frames and I think there's merit in what he says, even though I agree with *you* that a well-designed aluminum frame is as safe as a steel one. Tell you what would be *my* dream: a Tern Verge S11i made of titanium... of course, that might as well be made of "unobtanium" because I wouldn't be able to afford it.

Well, I made it through this second "Polar Vortex", but there's a lot of salt on the bike. As much as I'd like to be the "nightmare" rider for Tern, I can't bring myself to trash my Verge!

Cheers,

Steve

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Re: Tern Link D8 frame shearing in two

Post by Admin on Fri Apr 04, 2014 1:37 am

January 30, 2014 - 1:29am
Keith C. Johns





Country: USA

thor wrote:
Keith get over this alloy crap and metal fatique stuff you are constantly harping on. There were roughly 132 million bikes sold last year ... 90 % were alloy frames.That Number is pretty consisting over the last 10 or 20 ? years. IF alloy metal fatique would indeed be a problem, there would be thousands and hundred thousands of broken frames out there. Not so.  Steel is real ... comes from a clever advertising campaign. It has nothing to do with reality. When alloy frames hit the market some 30 years ago, it was indeed a problem with harsh ride or some frames breaking, that was 30 years ago. Even the bike industry as slow as it reacts sometimes, has learned a little bit.

In case of folding bikes, many many of them are alloy versus steel... lets talk about Dahon now, as I have some track record ( never had a broken Tern yet ) and guess what, despite that Dahon makes a lot of alloy framed bikes, I have more steel ones broken than alloys. Being the go-to guy in the US and sometimes worldwide, I receive an Ueber-Proportional amount of warranty or defective stuff..... in raw numbers, if I compare what I am selling its more steel breaks than alloy breaks.

While I am a loyal Dahon, and now turned Tern folding bike devotee, and I want to rally behind the troops after any disaster as you have, Thor, my first loyalty has always been to truth and scientific understanding of why things happen. I can't just blindly dismiss inconvenient facts. In the long run, Tern will be a better company if it reacts to defects by improving its designs. Choice of materials is integral to good engineering practice, and choosing the most durable materials is essential if a bike company wishes to make bikes which will last a lifetime.

What I am trying to get a grasp on is whether aluminum alloys are ultimately the best choice for durable bike frames. This thread is the first to show some real evidence to enlighten us in this area. I am not trying to condemn aluminum frames based on two instances out of milliions sold each year. These frames must be analyzed by engineers and this is premature to conclude what they will find. It might turn out to be a bad weld, rather than bad metal. Or a defect in a tube which is atypical of all the others out there. To be fair, we can not judge so soon.

I went to my local bike shop today, which sells Dahons thanks to my urging over many years. (I have tried to suggest Terns be considered also, but this too will take time.) I conducted an informal survey with two of their mechanics with wide experience in the industry. I asked, "You must occasionally receive returns of bikes due to catastrophic failure of their frames. Of all of these, what percentage have been on aluminum alloy frames versus steel frames?" Barry initially assumed I wanted to know just statistics for folding bikes, and said that very few had ever been returned for frame failures. But I told him I wanted to know about ALL bike types. He said that the vast majority of catastrophic frame defects had occurred on aluminum bike frames--only a few on steel comparatively. Mike came in and I posed the same question to him. He has been with this shop only a couple of years, but had many years working for Trek prior to this. He said that ALL the frame failures he had ever seen had been on aluminum alloy bike frames; never saw one on any steel bikes at all, with the exception of broken dropouts which he said was the weak point on most frames anyway. Then I asked about aluminum alloy components such as cranks and handlebars: had they seen many defects in these? Not really. That completed my very informal survey.

I admit that this was not a scientific survey because of the very small sample taken, but was anecdotally interesting because of these two guys' decades of experience collectively. The fact that few folding bikes had been returned may be related to the fact that, as I intimated earlier, a large percentage of folding bikes may not ever get heavy usage, sitting in storage for occasional use only, and if cyclic metal fatigue is occurring, it may never reveal itself for decades hence due to low frequency of period of use. But that doesn't guarantee immunity to those who regularly commute by folding bikes, and for whom the advantage of folding is primarily anti-theft and multi-modal transport rather than hide-away a bike for future use--these people subject their bikes to real-world type usage. So I focused my question on ALL bikes, to get the widest sampling of bikes used routinely under all conditions. I did not distinguish by brand or other types used. The conclusion of this unscientific survey is simply that based on average usage, aluminum frames tend to fail more frequently than steel by a large margin.

The only exception seems to be the other aluminum components used on bikes of different frame materials, which tend to not fail. This would include handlebars, cranks, seat posts, brake parts, wheel rims, quick release handles, and smaller parts generally. My guess is that these parts don't tend to fail because they are engineered for durabilty rather than light weight overall. I have a couple of aluminum cranks which I found discarded which snapped midway, and in all cases they were hollowed out for light weight rather than kept solid.

My working theory thus, pending further results from these two bikes in question, and further data from future bike frame failures, is that aluminum in and of itself is not specifically the cause of the failures, but that the engineering design is at fault, by giving in to the industry pressure to make bikes light weight to impress buyers by statistics, and under-engineering the frames to keep the weight down, and the lines looking clean and uncluttered (no longer using the diamond frame design with its powerful triangles but preferring a simpler single down-tube design). Steel being more resilient than aluminum, can take more abuse like this, but aluminum ought to be over-engineered because it is brittle and intolerant of poor engineering in favor of other factors. If these bike frames were designed with the same concern for strength as the majority of the components on these bikes, without yeilding to "make it lighter" and "make it look prettier" pressures, the frames would probably be able to be over-engineered enough to prevent failures. Even steel bikes yield to these industry pressures, and fail too, albeit in smaller quantities in at least one polled bike shop. If you make a bike out of paper-thin steel, to make it super light, it will fail, in spite of its being steel. And if you make it out of double the weight of aluminum as usual, it probably will never fail, in spite of being made of aluminum. So my suspicion of aluminum vs. steel assumes otherwise wise engineering design practices being used in either case: all things being equal, the steel bike will survive more abuse, but the aluminum bike might well outlive the steel bike IF PROPERLY DESIGNED.

But why build a bike out of aluminum, which costs more than steel, if you don't end up with a lighter bike for the extra cost? Good question. For to make a bike durable using aluminum, due to aluminum's inherently brittle and fracture-prone nature, you will end up with a heavier bike than an equally strong steel bike, and at a greater cost, too. So why bother? This makes me question the very choice of aluminum in frames generally. Yes, it can be made durable, but all the weight savings is lost in the process. The only remaining advantage will be anti-corrosion. But I think I'd rather have stainless steel for this.

The first priority seems to be to get the engineers to design DURABLE bikes rather than light weight bikes which look fancier. And choose the best materials for this purpose.


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Re: Tern Link D8 frame shearing in two

Post by Admin on Fri Apr 04, 2014 1:38 am

January 30, 2014 - 11:49am
thor

Country: USA




you are right Keith  in so many ways



By the way I like a classic steel bike with filet brazing and beautiful lug work.... there is something magical about it.

Your sampling is a little biased as of course they will receive many more alloy bikes than steel, cause there are so many more alloy bikes out there. Except if it is a "classic" retro trendy store who sells more steel bikes than usual, they sell 90 % alloy bikes. No wonder they get more alloy bikes back. Even if they get 80 % more broken alloy frames, than the % would still be below steel. Right ?

But your concerns about longevity are indeed warranted, no matter what material. Tern gets a lot of flack as even there top of theline products are just a tad heavier than most of the competition, guess where this tad more weight comes into play ... down the road 5 or 10 years from now. Thats the Tern Biz plan, they want to deliver a better longer lasting bike than all of the competition.

Best Thor


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Re: Tern Link D8 frame shearing in two

Post by Admin on Fri Apr 04, 2014 1:38 am


January 30, 2014 - 4:08pm
Re-tern





Country: UK




Just to clarify something here, my frame also broke at the weld the same as Lee's, I am almost certain this was not metal fatique in the aluminium alloy (I would like to point out that I am an experienjced mechanical engineer with  a background in inspection of aircraft so this isn't just a wild guess). The weld did appear to have been broken for a period of time as there was evidence of dirt/dust on the face of the welded flags which would have been on the inside of the tube. There was no evidence in the feeling of the way the bike rode that there was an pending issue; however I hadn't visually inspected the bike for a few weeks so I am unsure whether it would have been visible to the naked eye, but I doubt it. I understand also that steel frames can also suffer from breakages that is why I opted for the clear laquer Brompton, so as I can keep an eye on the frames condition without the paintwork getting in the way.


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Re: Tern Link D8 frame shearing in two

Post by Admin on Fri Apr 04, 2014 1:39 am


January 30, 2014 - 5:56pm
Steveroot

Country: USA


Hi, Re-tern,

You are certainly more qualified than I am to comment on the structural issues involved here! I'm a chemist-turned-dentist with a bit of machine-shop experience.

Your description of the contamination on the fracture faces is consistent with a progressive material failure, like the Strida crank axle image I posted above. It may be safe to say that this problem is rare (I hope so, at any rate!)... the problem then becomes how to identify a crack *in progress* so a catastrophic failure can be prevented. Your experience with aircraft I would guess resonates with this opinion.

The aluminum fractures I have experienced were all on natural (un-painted) surfaces, where I suspect you are right that I had better visibility. You would think (or at least *I* would think) that a crack in the metal underlying a layer of paint would resulti in a visible discontinuity in the paint. However, if it were located right at the edge of a weld, this might be difficult to see. It also seems possible that the crack could have been progressing to a fairly large extent without any sensation because aluminum is not as elastic as steel, then a bump or other sudden peak stress could have caused the sudden completion of the fracture.

I'm curious if the part of the fracture face that was dirty was on the bottom of the joint; I'd expect that location to be under more tensile stress and so more likely to begin to crack if it were going to happen. If this scenario is right, that would also somewhat explain why it wasn't apparent as the crack was developing. I can tell you I haven't paid much attention to the under-side of my frame... but I will now!

Glad you weren't hurt worse, and hopefully some useful information will be gotten out of your experience. Keep us posted.

Cheers,

Steve

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