Re: Thomson Elite Seatpost Failure

On 15 Apr, 18:23, Chalo <chalo.col...@xxxxxxxxx> wrote:
Nick L Plate wrote:

Chalo wrote:

If bandaging the thing up like a dog with a broken leg is acceptable,
then it doesn't matter whether the bike is made of CFRP, steel, zinc,
or Bakelite.  Likewise, duct tape is equally compatible with all frame
materials.

I've been considering what is the difference between bakelite and the
cabon fibre frame, and it is just the carbon.  Bakelite generally used
wood cellulose in the form of dust as the filler.  

The engineering phenolic materials I have used were reinforced with
linen fabric or cotton canvas.  It's extremely strong and resilient,
but it has the same shortcomings in principle as carbon-epoxy
composite.  That is, it has no ductility and limited ability to
sustain local damage while remaining structurally sound.  When it
reaches its limit, it tends to snap.

There is no reason
at all as far as I can see without thinking too hard, why a laminated
wood veneer bike frame is not constructed.  I'd be more likely to
trust a frame and forks which started out as a tree than some loose
bits of carbon.  As long as the bonding agent , forget the details of
bakelite, has some sort of temperature change in its setting then it
can be used with moulding wood veneer.  Think of the Mosquito, recon.
and fighter.

Wood in a bicycle application has the same set of structural tradeoffs
as CFRP or GFRP, but with lower strength.  It has the advantages of
being a renewable and resource-efficient material, as well as being
more aesthetically pleasing than plastic.

Wood cellulose fibres are hollow so the strength to weight ratio may
be higher than carbon or glass. It seems likely that it will also be
a more effective filler when highly compressed to minimise the
adhesive binding, due to its poor compressive strength. So a greater
proportion of the 'material' is the tubular structure of the wood
cells when compressed. And because of the difference in tensile and
compressive strength it's failure mode will be more progressive
because of the crushing of the wood cells. If bonded with the
'bakelite' polymer, it could be weakened with a small quantity f dust
so as to lower the potential surface energy in an overload condition
and cause a failure of the bonding at a more appropriate suface
tension so as to negate the fragmentation I have seen in racing cars
and recently at the world's track cycling champ's.

If your cotton or linen composites where highly pressurised, it would
seem likely that they would fare better. If they still fragmented
upon failure then a weakening of the bonding agent should help.
.

Relevant Pages

  • Wooden bikes, was Re: Materials suitable and unsuitable for bike frames
    ... on a TDF climb and he finishes ON THE BIKE AND WINS THE STAGE! ... some epoxy, the carbon fiber frame can be made as strong as new, albeit ... reasonably pack all the materials to repair the frame on a loaded ... wood cellulose in the form of dust as the filler. ...
    (rec.bicycles.tech)
  • Re: False analogies between accordions and violins/guitars (soundboards, wood, varnish etc)
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    (rec.music.makers.squeezebox)
  • Re: SWAGs on shop cost
    ... I know the actual price will vary with location, materials, and options, ... $12K for the slab & footings. ... I am building a timber frame metal clad shop. ...
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    ... materials and not typical of metallic materials ... commonly used in bicycles ... Catastrophic failure. ... the frame remains in continuous use since then. ...
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  • Re: CFRP drawbacks
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