Broken steel road bike fork
deja3...@bitrealm.com
were acting "grabby" in that the front would shimmy pretty
badly just as I'm coming to a stop. The rims felt a little
sticky, maybe some Gatorade got on them and it hasn't really
rained in a while. I cleaned the wheels last night and rode
into work today. It was still bad, but didn't seem as bad.
This has been going on for a week, I didn't think anything of
it. I decided to not ride after work and just come home, coming
down the driveway, the grabby-ness was really pronounced, so
I figure that the brake pads must be contaminated with something.
When I took the wheel off, my heart skipped a beat. Without much
effort, this is the result:
http://www.bitrealm.com/misc/fork/p1000783.jpg
http://www.bitrealm.com/misc/fork/p1000784.jpg
http://www.bitrealm.com/misc/fork/p1000785.jpg
It was hanging by no more than 2mm of steeel. I shudder when I
think of the roads I was about to go on, including one really
bad bump at the bottom. I don't think it would have held together
and when you lose the front like this, it's going to be bad.
The shimmy was the wheel moving back and forth due to the fork
leg being fatigued. There hasn't been any accident damage since
I put this fork on the bike. The crack was almost all the way
through, starting from the BACK of the fork leg.
Hank
> So, I've been noticing that the front brakes of my road bike
> were acting "grabby" in that the front would shimmy pretty
> badly just as I'm coming to a stop. The rims felt a little
> sticky, maybe some Gatorade got on them and it hasn't really
> rained in a while. I cleaned the wheels last night and rode
> into work today. It was still bad, but didn't seem as bad.
> This has been going on for a week, I didn't think anything of
> it. I decided to not ride after work and just come home, coming
> down the driveway, the grabby-ness was really pronounced, so
> I figure that the brake pads must be contaminated with something.
> When I took the wheel off, my heart skipped a beat. Without much
> effort, this is the result:
>
>
> It was hanging by no more than 2mm of steeel. I shudder when I
> think of the roads I was about to go on, including one really
> bad bump at the bottom. I don't think it would have held together
> and when you lose the front like this, it's going to be bad.
>
> The shimmy was the wheel moving back and forth due to the fork
> leg being fatigued. There hasn't been any accident damage since
> I put this fork on the bike. The crack was almost all the way
> through, starting from the BACK of the fork leg.
Yikes. Congrats on catching that before disaster struck.
semi-ambivalent
> So, I've been noticing that the front brakes of my road bike
> were acting "grabby" in that the front would shimmy pretty
> badly just as I'm coming to a stop. The rims felt a little
> sticky, maybe some Gatorade got on them and it hasn't really
> rained in a while. I cleaned the wheels last night and rode
> into work today. It was still bad, but didn't seem as bad.
> This has been going on for a week, I didn't think anything of
> it. I decided to not ride after work and just come home, coming
> down the driveway, the grabby-ness was really pronounced, so
> I figure that the brake pads must be contaminated with something.
> When I took the wheel off, my heart skipped a beat. Without much
> effort, this is the result:
>
>
> It was hanging by no more than 2mm of steeel. I shudder when I
> think of the roads I was about to go on, including one really
> bad bump at the bottom. I don't think it would have held together
> and when you lose the front like this, it's going to be bad.
>
> The shimmy was the wheel moving back and forth due to the fork
> leg being fatigued. There hasn't been any accident damage since
> I put this fork on the bike. The crack was almost all the way
> through, starting from the BACK of the fork leg.
You might invest in at least one lottery ticket about now. You know,
before it all wears off.
jim beam
chrome plate is bad for fatigue - it contains many fatigue initiators.
for the future, consider quality cfrp - unless abused, it's pretty much
"fatigue proof".
M-gineering
> through, starting from the BACK of the fork leg.
No surprise here, if they break, that's where they go
--
/Marten
info(apestaartje)m-gineering(punt)nl
raamman
> So, I've been noticing that the front brakes of my road bike
> were acting "grabby" in that the front would shimmy pretty
> badly just as I'm coming to a stop. The rims felt a little
> sticky, maybe some Gatorade got on them and it hasn't really
> rained in a while. I cleaned the wheels last night and rode
> into work today. It was still bad, but didn't seem as bad.
> This has been going on for a week, I didn't think anything of
> it. I decided to not ride after work and just come home, coming
> down the driveway, the grabby-ness was really pronounced, so
> I figure that the brake pads must be contaminated with something.
> When I took the wheel off, my heart skipped a beat. Without much
> effort, this is the result:
>
>
> It was hanging by no more than 2mm of steeel. I shudder when I
> think of the roads I was about to go on, including one really
> bad bump at the bottom. I don't think it would have held together
> and when you lose the front like this, it's going to be bad.
>
> The shimmy was the wheel moving back and forth due to the fork
> leg being fatigued. There hasn't been any accident damage since
> I put this fork on the bike. The crack was almost all the way
> through, starting from the BACK of the fork leg.
well, there you go, "steel is real" has been the mantra- but the
phrase " suseptable to rust" could be added. The fork looks very
clean, so I wonder how it happened to escape your notice earlier. I am
glad you escaped any mishap.
Peter Cole
If lugs aren't designed right they concentrate stress at the edges and
that's where they fatigue.
deja3...@bitrealm.com
This fork was on the bike for about 8 years and had probably around
12K miles on it in that time.
I would like to find a 1" threaded replacement that has eyelets for
fenders,
but they seem pretty thin on the ground. I can find the exact same
fork
shown here (in black) that I could still buy. It was a 200 mm steerer
tube with 35mm of threading. Cut, it is 190mm with 25mm of threading.
The one shown here was made for 27" wheels and I just run long reach
calipers. I had to have the crown race cut from 27 to 26.4mm.
If not, any 1" threadless forks with eyelets and room for fenders?
Anyone, Bueller?
Tim McNamara
<c5bce20d-a941-47d7...@k13g2000prh.googlegroups.com>,
deja3...@bitrealm.com wrote:
> On Sep 29, 5:42锟絘m, jim beam <m...@privacy.net> wrote:
> > On 09/28/2009 09:37 PM, deja3-u...@bitrealm.com wrote:
> >
> > > So, I've been noticing that the front brakes of my road bike were
> > > acting "grabby" in that the front would shimmy pretty badly just
> > > as I'm coming to a stop. 锟絋he rims felt a little sticky, maybe
> > > some Gatorade got on them and it hasn't really rained in a while.
> > > 锟絀 cleaned the wheels last night and rode into work today. 锟絀t
> > > was still bad, but didn't seem as bad. This has been going on for
> > > a week, I didn't think anything of it. 锟絀 decided to not ride
> > > after work and just come home, coming down the driveway, the
> > > grabby-ness was really pronounced, so I figure that the brake
> > > pads must be contaminated with something. When I took the wheel
> > > off, my heart skipped a beat. 锟絎ithout much effort, this is the
> > > result:
> >
> > >http://www.bitrealm.com/misc/fork/p1000783.jpg
> > >http://www.bitrealm.com/misc/fork/p1000784.jpg
> > >http://www.bitrealm.com/misc/fork/p1000785.jpg
> >
> > > It was hanging by no more than 2mm of steeel. 锟絀 shudder when I
> > > think of the roads I was about to go on, including one really bad
> > > bump at the bottom. 锟絀 don't think it would have held together
> > > and when you lose the front like this, it's going to be bad.
> >
> > > The shimmy was the wheel moving back and forth due to the fork
> > > leg being fatigued. 锟絋here hasn't been any accident damage since
> > > I put this fork on the bike. 锟絋he crack was almost all the way
> > > through, starting from the BACK of the fork leg.
The crack initiating in the back of the leg is not unusual.
> > chrome plate is bad for fatigue - it contains many fatigue
> > initiators.
Chrome plating *can* result in embrittlement but does not necessarily do
so. Millions of bikes and other load bearing appplications are chromed
without such failures happening.
The reason for the failure seem pretty self-evident in the photo. Note
how the crack followed the shore line of the socket so perfectly, and
note the relative thicknesses of the metal. Note also the lack on a
reinforcement tang on the inside of the fork leg.
> > for the future, consider quality cfrp - unless abused, it's pretty
> > much "fatigue proof".
More clueless advice from "jim beam."
> This fork was on the bike for about 8 years and had probably around
> 12K miles on it in that time.
>
> I would like to find a 1" threaded replacement that has eyelets for
> fenders, but they seem pretty thin on the ground. I can find the
> exact same fork shown here (in black) that I could still buy. It was
> a 200 mm steerer tube with 35mm of threading. Cut, it is 190mm with
> 25mm of threading. The one shown here was made for 27" wheels and I
> just run long reach calipers. I had to have the crown race cut from
> 27 to 26.4mm.
>
> If not, any 1" threadless forks with eyelets and room for fenders?
Harder to find these days since most aftermarket forks are aluminum or
CF, lack eyelets and are for 700C wheels (if the bike was made for 27"
wheels, going to a 700C fork will affect the geometry). But I would
think that any bike shop with a QBP account could order you a fork to
fit. Or you could have one made, but that would be expensive.
Frank Krygowski
> When I took the wheel off, my heart skipped a beat. Without much
> effort, this is the result:
>
>
> It was hanging by no more than 2mm of steeel. I shudder when I
> think of the roads I was about to go on, including one really
> bad bump at the bottom. I don't think it would have held together
> and when you lose the front like this, it's going to be bad.
Lucky you caught it when you did. Last year, our old custom tandem
let go of both blades simultaneously. The warnings I got were nowhere
near as explicit as yours. Fortunately, we were moving only about 10
mph at the time.
In my case, the bike was built by Jim Bradford, formerly of the
Atlanta, Georgia area. It was the last bike he built before getting
married and leaving on a honeymoon. I suspect he slapped in whatever
fork blades he had lying around in order to get the job done, because
the wall thickness was roughly one-third of the proper gage for
Reynolds 531 tandem forks.
I wish I could offer advice on how to choose a competent and ethical
frame builder, but I can't.
BTW, I think you shouldn't have too much trouble finding a
replacement. I was able to buy a replacement tandem fork from Tandems
Ltd in Alabama. For a single bike I intend to build, just last year I
was able to buy a chromed Japanese fork from Citybikes in Portland,
Oregon. http://www.citybikes.coop/
- Frank Krygowski
Jobst Brandt
>> When I took the wheel off, my heart skipped a beat. Without much
>> effort, this is the result:
http://www.bitrealm.com/misc/fork/p1000783.jpg
http://www.bitrealm.com/misc/fork/p1000784.jpg
http://www.bitrealm.com/misc/fork/p1000785.jpg
>> It was hanging by no more than 2mm of steel. I shudder when I
>> think of the roads I was about to go on, including one really bad
>> bump at the bottom. I don't think it would have held together and
>> when you lose the front like this, it's going to be bad.
> Lucky you caught it when you did. Last year, our old custom tandem
> let go of both blades simultaneously. The warnings I got were
> nowhere near as explicit as yours. Fortunately, we were moving only
> about 10 mph at the time.
> In my case, the bike was built by Jim Bradford, formerly of the
> Atlanta, Georgia area. It was the last bike he built before getting
> married and leaving on a honeymoon. I suspect he slapped in
> whatever fork blades he had lying around in order to get the job
> done, because the wall thickness was roughly one-third of the proper
> gage for Reynolds 531 tandem forks.
> I wish I could offer advice on how to choose a competent and ethical
> frame builder, but I can't.
> BTW, I think you shouldn't have too much trouble finding a
> replacement. I was able to buy a replacement tandem fork from
> Tandems Ltd in Alabama. For a single bike I intend to build, just
> last year I was able to buy a chromed Japanese fork from Citybikes
> in Portland, Oregon.
This is a classic fork failure in which the lug interface between fork
blade and fork crown had not been feathered after brazing. This
failure could be seen coming while "Cinelli" fork crowns that are
internally lugged, do not reveal their trend to failure until after
fracture. However after failure they were obvious failure points.
Many joints between lugs and frame tubes may be shiny chrome but they
have discontinuous transitions that cause fracture as in this one.
Jobst Brandt
someone
> Chrome plating *can* result in embrittlement but does not necessarily do
> so. Millions of bikes and other load bearing appplications are chromed
> without such failures happening.
More likely the cause of embrittlement is what causes it with non-
chromed forks. Overbrazed.
Current common practice is to use oxy-acetylene torch and spelter wire
because it is quicker overall. I suspect the higher temperatures
obtainable with oxy-acet ensure a deeper penetration of the spelter,
alloying with the steel, causing the embrittlement. In skilled
experienced hands, oxy-acet does produce excellent results when there
are no distractions. I would certainly favour a builder which had the
certification of qualification from a technical college in the use of
oxy-acetylene for brazing if I was unable to locate one with historic
recommendation. That (college cetificate) does not necessarily
qualify him to braze cycle forks. And be careful that builders
although say they do the work, leave spotty Nigel to do the
preperation.
Hearth brazed forks heated with natural gas may also suffer with
brass embrittlement due to excessive duration in the flame. Good
preparation is the key. No cutting with abrasive grit, only by file,
plenty of flux in the joint and the use of granular spelter inside the
end of the fork reduce the heat exposure of the steel so keeping the
alloying depth to a minimum at the edge of the crown. I think it be
the filling from the end of the crown rather the end of the fork to be
the killer.
Nigel, may of course used carbarundum instead of the file and scraper
to prepare the forks and crown and if he's applied a paste flux, how
much water?
>
> The reason for the failure seem pretty self-evident in the photo. Note
> how the crack followed the shore line of the socket so perfectly, and
> note the relative thicknesses of the metal. Note also the lack on a
> reinforcement tang on the inside of the fork leg.
Overbrazed.
>
> > > for the future, consider quality cfrp - unless abused, it's pretty
> > > much "fatigue proof".
>
> More clueless advice from "jim beam."
overbrazed.
someone
you're as bad as beam. The error is in the brazing. Plenty of aero
crowns and forks survive despite their 'design flaw'.
I used a 'full aero' crown on a Raleigh Competition for five years
with 531 light gauge forks with no ill effects. I repainted the frame
and forks in the last year and so know, because I gave it a careful
inspection, that there were no faults whatsoever in the
framebuilding. There did not appear to be any dressing of the lugs
following brazing, the cutouts were clear and the depth was consistent
all around with a tiny fillet. One 'fault', seat stay end cap had a
little gap in the braze, the gap was irrelevant and sealed by the
paint. The dent I put in the seat stay (crash) could not be covered
by paint.
jay
>
> - Show quoted text -
What is feathering?
someone
JB flapping.
Jobst Brandt
> What is feathering?
A fading out of one cross section into another where they meet:
http://www.gtgtandems.com/tech/brazing.html
The sudden step in cross section causes a stress concentration that
leads to cracking. Most better metal workers are aware of this.
Sadly the sloping fork crown of 1960's Cinellis were not feathered and
cracked for those of us who rode much. After two of these failures I
got a Masi Fork crown instead.
Feathering can be done as Hetchins did with curlicues and fade-outs,
or as Masi did with tapering pointed lugs.
Jobst Brandt
someone
> Jay Drew wrote:
> > What is feathering?
>
> A fading out of one cross section into another where they meet:
>
> http://www.gtgtandems.com/tech/brazing.html
like I said, JB flapping. That's about fillet joints not lugged, as
in the OP's photographs.
>
> The sudden step in cross section causes a stress concentration that
> leads to cracking.
No, you're flapping. and maybe you're cracking.
> Most better metal workers are aware of this.
> Sadly the sloping fork crown of 1960's Cinellis were not feathered and
> cracked for those of us who rode much.
Should have chosen a better metal worker, rather than one who would
fit such a terrible fork crown , and then overbraze it so you could
prove you rode much.
> After two of these failures I
> got a Masi Fork crown instead.
>
> Feathering can be done as Hetchins did with curlicues and fade-outs,
> or as Masi did with tapering pointed lugs.
The ovality of the fork blade spreads the strain so there is no
extraneous stress level.
jim beam
> Jay Drew wrote:
>
>> What is feathering?
>
> A fading out of one cross section into another where they meet:
>
> http://www.gtgtandems.com/tech/brazing.html
wrong. feathering is simply filing the edges of the lug.
>
> The sudden step in cross section causes a stress concentration that
> leads to cracking.
which is why it's not a straight cross section, it's got curved features
that mitigate - effectively radius reduction, a standard fatigue
mitigation technique.
> Most better metal workers are aware of this.
> Sadly the sloping fork crown of 1960's Cinellis were not feathered and
> cracked for those of us who rode much.
that's not feathering - that's radius reduction.
> After two of these failures I
> got a Masi Fork crown instead.
good for you. of course, if you'd understood what you were looking at
the first time, you'd only have suffered one failure...
>
> Feathering can be done as Hetchins did with curlicues and fade-outs,
> or as Masi did with tapering pointed lugs.
nope, that's radius reduction, not feathering. hetchins and masi [and
many others] do feather, but they do it with a file, and it's not a
function of lug shape.
jim beam
no it isn't jobst.
1. you don't know shit about fatigue.
2. you've failed to observe the fatigue interface.
3. you don't understand the nature of the loading forces.
4. you're completely ignorant of the effects of chrome plating.
> This
> failure could be seen coming while "Cinelli" fork crowns that are
> internally lugged, do not reveal their trend to failure until after
> fracture. However after failure they were obvious failure points.
er, this is not a cinelli fork. and the failure is not the same.
>
> Many joints between lugs and frame tubes may be shiny chrome but they
> have discontinuous transitions that cause fracture as in this one.
no, they cause fatigue. fatigue causes fracture. what did you learn at
stanford jobst? analysis and logic were obviously absent from your
curriculum.
jim beam
> In article
> <c5bce20d-a941-47d7...@k13g2000prh.googlegroups.com>,
> deja3...@bitrealm.com wrote:
>
>>> On 09/28/2009 09:37 PM, deja3-u...@bitrealm.com wrote:
>>>
>>>> So, I've been noticing that the front brakes of my road bike were
>>>> acting "grabby" in that the front would shimmy pretty badly just
>>>> some Gatorade got on them and it hasn't really rained in a while.
>>>> was still bad, but didn't seem as bad. This has been going on for
>>>> after work and just come home, coming down the driveway, the
>>>> grabby-ness was really pronounced, so I figure that the brake
>>>> pads must be contaminated with something. When I took the wheel
>>>> result:
>>>
>>>> http://www.bitrealm.com/misc/fork/p1000783.jpg
>>>> http://www.bitrealm.com/misc/fork/p1000784.jpg
>>>> http://www.bitrealm.com/misc/fork/p1000785.jpg
>>>
>>>> think of the roads I was about to go on, including one really bad
>>>> and when you lose the front like this, it's going to be bad.
>>>
>>>> The shimmy was the wheel moving back and forth due to the fork
>>>> I put this fork on the bike. �The crack was almost all the way
>>>> through, starting from the BACK of the fork leg.
>
> The crack initiating in the back of the leg is not unusual.
>
>>> chrome plate is bad for fatigue - it contains many fatigue
>>> initiators.
>
> Chrome plating *can* result in embrittlement but does not necessarily do
> so. Millions of bikes and other load bearing appplications are chromed
> without such failures happening.
>
> The reason for the failure seem pretty self-evident in the photo. Note
> how the crack followed the shore line of the socket so perfectly, and
> note the relative thicknesses of the metal. Note also the lack on a
> reinforcement tang on the inside of the fork leg.
oh, timmy the retard is now a fatigue expert!!! tell us timmy, which
end of the microscope did you cram up your ass when you learned all this
bullshit?
>
>>> for the future, consider quality cfrp - unless abused, it's pretty
>>> much "fatigue proof".
>
> More clueless advice from "jim beam."
which is the larger force timmy - 1600N or 5000N?
>
>> This fork was on the bike for about 8 years and had probably around
>> 12K miles on it in that time.
>>
>> I would like to find a 1" threaded replacement that has eyelets for
>> fenders, but they seem pretty thin on the ground. I can find the
>> exact same fork shown here (in black) that I could still buy. It was
>> a 200 mm steerer tube with 35mm of threading. Cut, it is 190mm with
>> 25mm of threading. The one shown here was made for 27" wheels and I
>> just run long reach calipers. I had to have the crown race cut from
>> 27 to 26.4mm.
>>
>> If not, any 1" threadless forks with eyelets and room for fenders?
>
> Harder to find these days since most aftermarket forks are aluminum or
> CF, lack eyelets and are for 700C wheels (if the bike was made for 27"
> wheels, going to a 700C fork will affect the geometry). But I would
> think that any bike shop with a QBP account could order you a fork to
> fit. Or you could have one made, but that would be expensive.
what ridiculous retardation.
jim beam
> On Tue, 29 Sep 2009 05:42:51 -0700, jim beam<m...@privacy.net> wrote:
>
>> for the future, consider quality cfrp - unless abused, it's pretty much
>> "fatigue proof".
>
> failing catastrophically (like crappy fiber does when it fails) is the
> only thing that saved him.
er, so a failure is better than a non-failure??? because you're
confused between fatigue and over-load or abuse??? jeepers dude, you're
winning that stupidity contest again!
>
> As always, your advice is useless.
no, i cast pearls before ignorant incapable swine.
jim beam
no shit.
Frank Krygowski
> On 09/29/2009 03:15 PM, Jobst Brandt wrote:
>
> > Jay Drew wrote:
>
> >> What is feathering?
>
> > A fading out of one cross section into another where they meet:
>
> > http://www.gtgtandems.com/tech/brazing.html
>
> wrong. feathering is simply filing the edges of the lug.
>
>
>
> > The sudden step in cross section causes a stress concentration that
> > leads to cracking.
>
> which is why it's not a straight cross section, it's got curved features
> that mitigate - effectively radius reduction, a standard fatigue
> mitigation technique.
Not surprisingly, jim beam has things exactly backwards. When
blending a transition from a larger sized piece (like the lug) to a
smaller sized piece (like the fork blade) the idea is to increase, not
decrease the radius. The ultimate in radius _reduction_ would be a
sharp corner, which generates a high stress concentration. Large
radii are the opposite and generate lower stress concentrations.
You can play around with different radius values at
http://www.fatiguecalculator.com/cgi-bin/findkt.pl
to investigate this.
For example, for D=25 mm, d = 23 mm and r=1 mm, the stress
concentration factor is 1.84 - that is, peak stress in the area of the
shoulder will be 1.84 times the stress further away. If you reduce
the radius (as jim seems to recommend) to 0.1 mm, the stress
concentration factor jumps to 3.52
- Frank Krygowski
jim beam
> On Sep 29, 10:40�pm, jim beam<m...@privacy.net> wrote:
>> On 09/29/2009 03:15 PM, Jobst Brandt wrote:
>>
>>> Jay Drew wrote:
>>
>>>> What is feathering?
>>
>>> A fading out of one cross section into another where they meet:
>>
>>> �http://www.gtgtandems.com/tech/brazing.html
>>
>> wrong. �feathering is simply filing the edges of the lug.
>>
>>
>>
>>> The sudden step in cross section causes a stress concentration that
>>> leads to cracking.
>>
>> which is why it's not a straight cross section, it's got curved features
>> that mitigate - effectively radius reduction, a standard fatigue
>> mitigation technique.
>
> Not surprisingly, jim beam has things exactly backwards. When
> blending a transition from a larger sized piece (like the lug) to a
> smaller sized piece (like the fork blade) the idea is to increase, not
> decrease the radius. The ultimate in radius _reduction_ would be a
> sharp corner, which generates a high stress concentration. Large
> radii are the opposite and generate lower stress concentrations.
you're a fraud and moral retard krygowski. you knew exactly what i
meant before you tried putting false words in my mouth - the concept of
decreasing radius sharpness is something so simple and obvious, even a
failed phd candidate like you should be able to grasp it.
>
> You can play around with different radius values at
> http://www.fatiguecalculator.com/cgi-bin/findkt.pl
> to investigate this.
>
> For example, for D=25 mm, d = 23 mm and r=1 mm, the stress
> concentration factor is 1.84 - that is, peak stress in the area of the
> shoulder will be 1.84 times the stress further away. If you reduce
> the radius (as jim seems to recommend) to 0.1 mm, the stress
> concentration factor jumps to 3.52
you're a fraud and moral retard krygowski. resign and stop fucking up
people's careers.
bjwe...@gmail.com
It doesn't have anything to do with rust or cleanliness.
There is a bit of surface oxidation inside the fork,
but it's totally superficial.
There is a stress concentration where the fork
crown meets the blade. The joint was possibly
overheated during manufacture leading to a
weakness at the braze. The crack initiated at
the rear of the fork, at the place where the crown
meets the blade, and propagated forward.
You can kind of see this from the pictures
http://www.bitrealm.com/misc/fork/p1000784.jpg
Along the broken surface, at the upper right it's
fairly dark, which indicates it's been cracked
for a while and exposed to atmosphere, dirt etc.
This is where the crack follows the line of the crown.
Along the front of the fork blade, the line of breakage
is more smooth than scalloped, as if it were just
torn away, and the surface looks cleaner. This is
what was still attached until the final break
happened.
If the OP could take an in-focus close up picture
of the fracture surfaces (ideally in side lighting,
with a tripod) it would probably show the differences
in texture of the initial and final fractured surfaces
clearly.
It looks like the fork was cracked almost halfway
around for a while before the final rupture.
Any material can fail if there is a flaw in the design
or manufacture. Steel is no panacea, but neither
is anything else. iIt's probably because it was steel
that the fork was "rideable" for a while even though
cracked, but whether that is good or bad depends
on your ideas about fault detection. (That is,
a piece that cracks instantly is bad, but a piece that
lulls you into still riding it around even though it's
about to finally give way and drop you is also bad.)
Ben
jim beam
disagree - this is not a typical fatigue fracture. the fact that part
of the crown has come away with the blade is testament to that - highly
unusual.
more likely is a combination of poor brazing leaving a gap between the
crown and the blade. subsequent chroming would leave chromic acid
deposits [and others] which would partially erode both the blade and the
crown, and initiate fatigue. the rest is simply fatigue propagation.
>
> If the OP could take an in-focus close up picture
> of the fracture surfaces (ideally in side lighting,
> with a tripod) it would probably show the differences
> in texture of the initial and final fractured surfaces
> clearly.
it's not just the fracture surfaces that is of interest, it's the
initiation point.
>
> It looks like the fork was cracked almost halfway
> around for a while before the final rupture.
>
> Any material can fail if there is a flaw in the design
> or manufacture. Steel is no panacea, but neither
> is anything else.
cfrp is highly fatigue resistant - it would not fail in this manner.
> iIt's probably because it was steel
> that the fork was "rideable" for a while even though
> cracked,
that ben, is utter garbage. any material undergoing fatigue is
"rideable" until it fails.
> but whether that is good or bad depends
> on your ideas about fault detection. (That is,
> a piece that cracks instantly is bad,
that's not fatigue, that's simply fracture.
> but a piece that
> lulls you into still riding it around even though it's
> about to finally give way and drop you is also bad.)
this is what is so dangerous about fatigue and why so many millions of
dollars are spent on detection every year - pre-failure symptoms are not
obvious and need skill, awareness and usually testing gear to detect.
undetected failure can be tragic. everyone should periodically inspect
their bike for this kind of stuff.
Frank Krygowski
> On 09/29/2009 09:04 PM, Frank Krygowski wrote:
>
> > On Sep 29, 10:40 pm, jim beam<m...@privacy.net> wrote:
>
> >>> leads to cracking.
>
> >> which is why it's not a straight cross section, it's got curved features
> >> that mitigate - effectively radius reduction, a standard fatigue
> >> mitigation technique.
>
> > Not surprisingly, jim beam has things exactly backwards. When
> > blending a transition from a larger sized piece (like the lug) to a
> > smaller sized piece (like the fork blade) the idea is to increase, not
> > decrease the radius. The ultimate in radius _reduction_ would be a
> > sharp corner, which generates a high stress concentration. Large
> > radii are the opposite and generate lower stress concentrations.
>
> you're a fraud and moral retard krygowski. you knew exactly what i
> meant before you tried putting false words in my mouth - the concept of
"jim," I didn't put words in your mouth. I quoted exactly what you
said.
You had it exactly backwards. If you had any class at all, you'd have
simply said "Oops, my mistake. I meant to say..."
- Frank Krygowski
someone
I have made this kind of fracture at thre other end of the forks when
attempting to correct a build error. You know, cold set the forks.
New fork blades ,I was bending them but they wouldn't give, used
alittle more leverage than I expected and they snapped. Checked with
my trusted framebuilder, and he said "Nio, they shouldn't have done
that. You just cold set the forks after brazing." The coarse
granularity of what was steel was caused by an excess of spelter being
absorbed due to prolonged and/or excessive heat. There was no chrome,
only paint. The 'steel' failed in tension with two applications of
force. The point is the metal would not yield, it could only
fracture. The klutz who had 'brazed' the forks had turned the
advanced steel into a similar metal to cast iron. Only the colour of
fracture was different. This had the slightest tinge of yellow where
one would expect blue or neutral. Cast iron is grey with variations
of shade in the granulation.
Michael Press
<ff4e057a-0963-4839...@q40g2000prh.googlegroups.com>,
deja3...@bitrealm.com wrote:
> So, I've been noticing that the front brakes of my road bike
> were acting "grabby" in that the front would shimmy pretty
> badly just as I'm coming to a stop. The rims felt a little
> sticky, maybe some Gatorade got on them and it hasn't really
> rained in a while. I cleaned the wheels last night and rode
> into work today. It was still bad, but didn't seem as bad.
> This has been going on for a week, I didn't think anything of
> it. I decided to not ride after work and just come home, coming
> down the driveway, the grabby-ness was really pronounced, so
> I figure that the brake pads must be contaminated with something.
> When I took the wheel off, my heart skipped a beat. Without much
> effort, this is the result:
>
> http://www.bitrealm.com/misc/fork/p1000783.jpg
> http://www.bitrealm.com/misc/fork/p1000784.jpg
> http://www.bitrealm.com/misc/fork/p1000785.jpg
>
> It was hanging by no more than 2mm of steeel. I shudder when I
> think of the roads I was about to go on, including one really
> bad bump at the bottom. I don't think it would have held together
> and when you lose the front like this, it's going to be bad.
>
> The shimmy was the wheel moving back and forth due to the fork
> leg being fatigued. There hasn't been any accident damage since
> I put this fork on the bike. The crack was almost all the way
> through, starting from the BACK of the fork leg.
I am happy for you. Now Mr. Mom. If I said it once, I
said it a dozen times, when your bike acts wonky,
dismount and determine the cause. Do not ride an
un-diagnosed wonky bike.
--
Michael Press
bjwe...@gmail.com
> On 09/29/2009 10:01 PM, b...@mambo.ucolick.org wrote:
>
> > Any material can fail if there is a flaw in the design
> > or manufacture. Steel is no panacea, but neither
> > is anything else.
>
> cfrp is highly fatigue resistant - it would not fail in this manner.
>
> > iIt's probably because it was steel
> > that the fork was "rideable" for a while even though
> > cracked,
>
> that ben, is utter garbage. any material undergoing fatigue is
> "rideable" until it fails.
Ah, Beamer. It's always good to have you disagree
with me. When you follow up a post of mine with a
message of agreement, I feel the need to recheck
my calculations.
CFRP is highly fatigue resistant - if it's strong enough
and doesn't have any construction flaws. On the other
hand, so is steel. Saying a CFRP fork wouldn't fail in
this manner is a bit meaningless because the fork
failed from fatigue initiated by a construction error and
worsened by a stress riser
(a brazing problem most likely, possibly worsened by
chroming as you argue, but most chromed forks
don't fail, so that brings us back to an initial assembly
error).
CFRP parts obviously don't fail from brazing
errors, but they certainly can fail from construction
errors and stress risers. My impression is that CF
bike parts tend to have a fairly large reserve strength
because they'll break quickly once they start breaking,
so manufacturers want to avoid the start of breakage
at all. (The exception might be superlight wheels, but
those tend to get banged up in use, and I'm excluding
crash damage from this discussion.)
Any part with a fatigue crack or flaw is rideable until it fails,
the question is how long it takes from the crack becoming
significant until full failure. For example, this fork was
cracked halfway around and still rideable (sort of) and
it sounds like that was going on for several days. An
aluminum part that was cracked halfway around probably
wouldn't last that long before failing completely. This
is conjecture on my part since I have never cracked
an aluminum fork like that, but it seems to me that
with aluminum frames and parts, they make the transition
from cracked to doomed very quickly. This is by no
means an argument against aluminum parts - you won't
catch me riding with steel cranks.
> > but whether that is good or bad depends
> > on your ideas about fault detection. (That is,
> > a piece that cracks instantly is bad,
>
> that's not fatigue, that's simply fracture.
I meant a piece that transitions from fatigue crack
to total failure quickly. You don't want that because
by the time you figure out something feels wrong,
you're already on the deck. Bad old titanium BB
spindles were probably in this category. Not
necessarily because titanium is evil, it's just not
good in that application.
>
> > but a piece that
> > lulls you into still riding it around even though it's
> > about to finally give way and drop you is also bad.)
>
> this is what is so dangerous about fatigue and why so many millions of
> dollars are spent on detection every year - pre-failure symptoms are not
> obvious and need skill, awareness and usually testing gear to detect.
> undetected failure can be tragic. everyone should periodically inspect
> their bike for this kind of stuff.
Well, yes, though in this case the rider did notice something
funny beforehand. It's always hard to know what's just
voodoo and what's a real problem, but when the bike starts
acting odd it's time to start taking pieces off and wiggling
things. If nothing falls apart in your hands, you can always
put it back together.
Ben
someone
Aluminium, its alloys and steel all have the advantage that they will
yield before fracture. Faulty brazing may remove this property. I
have experienced this period of yield with aluminium handlebars which
were drooping from the stem, one side tore on the top and the bar
dropped quite some way before I had transferred sufficient weight to
stop the discection. The bars had obviously fatigued but they had
also yielded at the same time and during the final give. There is no
time to take action when a CFRP part is in its final stage of failure,
modification with cellulose fibre such as flax may help to mitigate
the speed of failure.
Frank Krygowski
> ... There is no
> time to take action when a CFRP part is in its final stage of failure,
> modification with cellulose fibre such as flax may help to mitigate
> the speed of failure.
Hey, I see a long term strategy for Rivendell! Instead of carbon
fiber frames, Grant can build frames of flax fiber!
Wool, beeswax, canvas and flax. It fits!
- Frank Krygowski
someone
Early bicycle frames were made from cellulose fibre, velocipede,
drassienne, boneshaker.
RonSonic
Sometimes Kevlar or to get really fancy a titanium mesh is laid up in the
composite for insurance.
--
Oh damn. There's that annoying blog. Again. http://dumbbikeblog.blogspot.com