Re: Thomson Elite Seatpost Failure

Nick L Plate wrote:
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.

Alas, it isn't.


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.

The goal in laminating composites is to use as little of the matrix material as possible. It really contributes nothing to the bulk strength. Modest compression is generally used when doing layups.

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.

When laminated structures are bent, there is a shear stress developed between the lamina, leading to delamination. Structural integrity is lost, leading to fiber failure, the ultimate failure mechanism.
.

Relevant Pages

  • Re: Thomson Elite Seatpost Failure
    ... used wood cellulose in the form of dust as the filler. ... Today's exterior-rated plywood still mostly uses phenol formaldehyde resin, the same resin used in Bakelite. ... I'm using exterior plywood with fiberglass taped seams, but for filler, I'm using epoxy thickened with wood "flour" (dust), same filler as Bakelite -- not particularly strong. ...
    (rec.bicycles.tech)
  • Re: what material is this ?
    ... I found this old electric clock and I'd like to paint it. ... e-bay. ... The case is not wood, it's not bakelite and it's not plastic. ...
    (alt.horology)
  • Re: hard stuff that will bond to wood
    ... of using resorcinol glue, the old-fashioned boat-building stuff? ... It's hard like bakelite and sticks wickedly to wood, ... presence of moisture. ...
    (rec.music.makers.builders)
  • Re: what material is this ?
    ... One of the ingredients of Bakelite is wood fiber. ... Wood flour is just what it sound like - wood that has been ground to a powder. ... In wood fiber materials it is usually possible to see the stringy fibers especially at an edge or break but not in bakelite because the wood filler starts out as a dust. ...
    (alt.horology)