guess when aluminum fork may be nearing 'end of useful life'?

guess when aluminum fork may be nearing 'end of useful life'?

Post by wle.. » Sat, 17 Dec 2011 06:39:25


is there any way to guess when an aluminum fork may be nearing its
'end of useful life'?

mine has 35,000 miles

rider weight has always been under 150 lbs

bike is 20

it;s  a unicrown, racing bike, 1999 or so, fork, possibly a GT
not particularly light or delicate
not displaying any visible problems

that is all i know!

oh
roads are  moderately bumpy around here, not ridiculous

so how do they estimate that?
and how long is it estimated for?
i would guess some kind  of process like this:
(ADM average deflection in mm) * (ND number of deflections) <= X
(          average deflection in mm) * (      number of deflections)
<= X

what is ADM, ND, and X?

then if i could estimate DPM [deflections per mile], i could guess end
of life

this is all supposition

how do designers really do it?

wle

 
 
 

guess when aluminum fork may be nearing 'end of useful life'?

Post by wle.. » Sun, 18 Dec 2011 22:44:09

great
no one knows
something technical on rec.bikes.tech, and no one can even guess
wle

 
 
 

guess when aluminum fork may be nearing 'end of useful life'?

Post by Lou Holtma » Mon, 19 Dec 2011 00:34:16


Quote:
> great
> no one knows
> something technical on rec.bikes.tech, and no one can even guess
> wle

What do you prefer a bullshit answer?

Lou

 
 
 

guess when aluminum fork may be nearing 'end of useful life'?

Post by AMuz » Mon, 19 Dec 2011 00:51:21

Quote:

> great
> no one knows
> something technical on rec.bikes.tech, and no one can even guess

That's right.

We don't know if it's welded or bonded, we don't know the
service history and, even if we did, likelihood of failure
is a supposition based on best-guess probabilities not a
date certain.

If you have serious reservations, especially if it's had the
usual impacts, dings, slings and arrows of commuting
mileage, just buy a fork. They are cheap.

--
Andrew Muzi
  <www.yellowjersey.org/>
  Open every day since 1 April, 1971

 
 
 

guess when aluminum fork may be nearing 'end of useful life'?

Post by David Scheid » Mon, 19 Dec 2011 02:17:26

:> great
:> no one knows
:> something technical on rec.bikes.tech, and no one can even guess

:That's right.

:We don't know if it's welded or bonded, we don't know the
:service history and, even if we did, likelihood of failure
:is a supposition based on best-guess probabilities not a
:date certain.

:If you have serious reservations, especially if it's had the
:usual impacts, dings, slings and arrows of commuting
:mileage, just buy a fork. They are cheap.

What do you guys like for replacing 1" forks these days?  700c, needs
to clear 35mm tires plus fender, eyelet for fenders, prefer caliper
brake (not strongly, but it's what the bike's got).  slight preference
for threadless, but no big deal, since the fork is french and will
need new stem, bars, and headset anyway.  

--
sig 114

 
 
 

guess when aluminum fork may be nearing 'end of useful life'?

Post by AMuz » Mon, 19 Dec 2011 03:09:28

Quote:



> :> great
> :> no one knows
> :> something technical on rec.bikes.tech, and no one can even guess

> :That's right.

> :We don't know if it's welded or bonded, we don't know the
> :service history and, even if we did, likelihood of failure
> :is a supposition based on best-guess probabilities not a
> :date certain.

> :If you have serious reservations, especially if it's had the
> :usual impacts, dings, slings and arrows of commuting
> :mileage, just buy a fork. They are cheap.

> What do you guys like for replacing 1" forks these days?  700c, needs
> to clear 35mm tires plus fender, eyelet for fenders, prefer caliper
> brake (not strongly, but it's what the bike's got).  slight preference
> for threadless, but no big deal, since the fork is french and will
> need new stem, bars, and headset anyway.  

Your bike had a metric threaded aluminum fork with clearance
for 700-35 plus mudguards? Odd item, that.

A 1" threaded touring fork with cantis is relatively popular
but without brake mounts will be less common hence more
expensive. (race bike forks are a dirt cheap commodity)

--
Andrew Muzi
  <www.yellowjersey.org/>
  Open every day since 1 April, 1971

 
 
 

guess when aluminum fork may be nearing 'end of useful life'?

Post by Frank Krygowsk » Mon, 19 Dec 2011 03:16:37

Quote:

> great
> no one knows
> something technical on rec.bikes.tech, and no one can even guess
> wle

For a mechanical part used in predictable and calculable conditions, a
designer can compute or estimate the percentage of cycles the part will
see each level of fatigue stress.  For example, a machine shaft might
have 400 revolutions with low bending stress, then 200 revs at a higher
stress, etc.  There's a technique called Miner's Rule which is used to
compute a single equivalent value of reversing stress.  That level of
stress can be compared to S-n (fatigue) data for the alloy in question,
to estimate service life.

But it's all pretty complicated and relies heavily on assumptions for
what I'd call fudge factors - for example, assumptions of stress
concentration factors, size factors, material factors, etc. If stresses
are not reversing, but instead varying (a reversing component
superimposed on an average non-zero value) there's a method for
addressing that.  It's all a pretty good project even for a device whose
loads are known.

For a device like a bike fork, loads are not really known, so little of
the above applies.  I imagine that a large and competent manufacturer
would have prototypes built using some pretty crude assumptions, and
subject them to fatigue testing, with larger loads than would be
expected in any real-life situation.  I imagine smaller manufacturers
might have designers who would say "Oh, that's probably good enough.
And look how light it is!"  No way to tell where you are in that
spectrum - although most small builders used steel forks instead.

FWIW, our custom-built Reynolds 531 tandem had its steel fork blades
suddenly snap off.  Turns out the builder (Jim Bradford, then of the
Atlanta, GA area) had used track gage fork blades, one third the wall
thickness of Reynold's tandem gage blades.  Of course, I didn't know
that until I measured the broken blades.

--
- Frank Krygowski

 
 
 

guess when aluminum fork may be nearing 'end of useful life'?

Post by thirty-si » Mon, 19 Dec 2011 03:04:48


Quote:
> is there any way to guess when an aluminum fork may be nearing its
> 'end of useful life'?

Dice.

Quote:

> mine has 35,000 miles

> rider weight has always been under 150 lbs

> bike is 20

> it;s ?a unicrown, racing bike, 1999 or so, fork, possibly a GT
> not particularly light or delicate
> not displaying any visible problems

> that is all i know!

> oh
> roads are ?moderately bumpy around here, not ridiculous

> so how do they estimate that?
> and how long is it estimated for?
> i would guess some kind ?of process like this:
> (ADM average deflection in mm) * (ND number of deflections) <= X
> ( ? ? ? ? ?average deflection in mm) * ( ? ? ?number of deflections)
> <= X

> what is ADM, ND, and X?

> then if i could estimate DPM [deflections per mile], i could guess end
> of life

> this is all supposition

> how do designers really do it?

By looking at previous models.  A big company will test its products.
Unless you are overloading the fork by lugging building materials (or
whatever) then its likely your big name forks will outlive you if you
never crash them.  The tests involve continuous bumping a human would
not wish to endure for two minutes and will possibly continue for
three to six months without failure.  I'd expect a normal endurance
limit exceeding 250,000 miles, although the equipment is not tested
with normal riding.
 
 
 

guess when aluminum fork may be nearing 'end of useful life'?

Post by Dan » Mon, 19 Dec 2011 04:02:28


Quote:
> is there any way to guess when an aluminum fork may be nearing its
> 'end of useful life'?

If it doesn't get any perishable sauce burned on the first time you
use it to line a pan and wrap leftovers, you could easily still re-use
it as a skillet lid.  After that it's out with the trash.
 
 
 

guess when aluminum fork may be nearing 'end of useful life'?

Post by Dan » Mon, 19 Dec 2011 04:05:50


Quote:

> > is there any way to guess when an aluminum fork may be nearing its
> > 'end of useful life'?

> If it doesn't get any perishable sauce burned on the first time you
> use it to line a pan and wrap leftovers, you could easily still re-use
> it as a skillet lid.  After that it's out with the trash.

Oh... "fork".  Well, if it creaked or felt floppy or showed any
visible damage I'd throw it away.
 
 
 

guess when aluminum fork may be nearing 'end of useful life'?

Post by Dan » Mon, 19 Dec 2011 04:31:07


Quote:

> > is there any way to guess when an aluminum fork may be nearing its
> > 'end of useful life'?

> Dice.

> > mine has 35,000 miles

> > rider weight has always been under 150 lbs

> > bike is 20

> > it;s  a unicrown, racing bike, 1999 or so, fork, possibly a GT
> > not particularly light or delicate
> > not displaying any visible problems

> > that is all i know!

> > oh
> > roads are  moderately bumpy around here, not ridiculous

> > so how do they estimate that?
> > and how long is it estimated for?
> > i would guess some kind  of process like this:
> > (ADM average deflection in mm) * (ND number of deflections) <= X
> > (          average deflection in mm) * (      number of deflections)
> > <= X

> > what is ADM, ND, and X?

> > then if i could estimate DPM [deflections per mile], i could guess end
> > of life

> > this is all supposition

> > how do designers really do it?

> By looking at previous models.  A big company will test its products.
> Unless you are overloading the fork by lugging building materials (or
> whatever) then its likely your big name forks will outlive you if you
> never crash them.  The tests involve continuous bumping a human would
> not wish to endure for two minutes and will possibly continue for
> three to six months without failure.  I'd expect a normal endurance
> limit exceeding 250,000 miles, although the equipment is not tested
> with normal riding.

Normal riding for me involves things like:  Uh-oh, long freight train
ahead.  Cagers queue up and stop.  I turn right and follow tracks w/
the train until it passes, cross cagerland cluster, into residential
neighborhood.  Over another set of tracks, into a school back lot,
down a windy narrow drive w/ two speed bumps to bunny hop, through the
front parking lot... where I must have looked back and noticed my
clothes were gone off the rear rack.  (T-shirt too good to abandon.)
Backtracked to the last RR crossing, where I found my clothes.  The
bike catches a lot of air and on / off road transitions.  I would
probably notice if the fork was wonky.  All my bikes have steel forks,
though.  (Breaking a fork - ouch!)
 
 
 

guess when aluminum fork may be nearing 'end of useful life'?

Post by Michael Pres » Tue, 20 Dec 2011 07:58:54

In article

Quote:

> great
> no one knows
> something technical on rec.bikes.tech, and no one can even guess

You want people you do not know who
know nothing about your fork, or history,
who have not examined that particular
fork with the latest analytic tools such
as slow neutron spectroscopy to tell you
if your fork is safe to ride? Yeah, sure;
it's good. Ride it down any mountainside
that pleases you.

--
Michael Press