Re: more cfrp bleating

Peter Cole wrote:
An interesting paper on the challenges presented in designing a crashworthy CF composite aircraft:

<http://nlr.nl/smartsite.dws?id=4366>

A couple of quotes:

"Traditionally, fuselages of fixed-wing transport aircraft
are made mostly of aluminium, a material with
considerable capacity for plastic deformation, hence,
an inherent capability to absorb energy in crash
situations. Since the last two decades, composite
materials are used more extensively to build aircraft
structures, although in civil transport aircraft, applications are limited mainly to the empennage, the
outer wing and secondary structures. However,
application of composite materials to aircraft fuselages
becomes feasible rapidly, and the crashworthiness
aspect related to composite structures has become a
serious issue. The composites used for aerospace
structures are generally brittle materials with hardly
any capacity for plastic deformation, so
crashworthiness is no longer a materials aspect, but
requires a combined materials/structures/fabrication approach."

that's a fundamental misunderstanding. cfrp absorbs substantial energy as it breaks - it's extremely tough, remember?



"Metals absorb energy by plastic deformation. For
metal structures, this applies to all failure modes:
tension, compression, bending, etc. Composites
absorb energy mainly by fiber breakage. It is important
to break a fiber many times over, rather than once
only. For composite structures, this seems possible only in a compression mode without buckling, i.e., in a
stabilized configuration. Failure in tension or bending
usually doesn't lead to multiple fiber fractures.
Helicopter technology has indicated that carbon-fibers
are best for energy absorption, and aramid fibers are
best to provide stability and integrity of a crushing
structure. Solutions are therefore sought in mixed
laminates of both fiber types, either as a laminate with
different material plies or as hybrid fabrics."

and?



It is also interesting to note in light of the Boeing flap, that the drop test documented here produced results that didn't conform to the model (for the overall structure), supporting the argument that full scale drop tests may be the wisest way to go until the engineering is better understood.

The important point contained in this document, from a bicycle component point of view, is that CF composites are typically very bad at absorbing energy,

absolutely incorrect. they absorb substantial energy - they just do it differently!


with the contrary sounding reality that CF composite structures with very good energy absorbency can be designed.

how inconvenient to everything you've just said!

Unfortunately, bicycle components are not made that way, and consequently retain the brittle characteristics of the base material.

says who??? that's a massive presumption, and a completely wrong one if the torn head tube example is anything to go by.



Energy absorbency in the form of gross crashes is probably not nearly as important as cumulative low impact damage in bicycle components and the ability to detect it, but it's still a consideration.

what is "impact"??? a 0.1ms^-1 collision with a dead chicken? or a 100ms^-1 collision with a tungsten spike of 60 degree cone tip angle, 0.001mm tip radius and connected to a 2,000kg pendulum? unless you define "impact", it means _nothing_.

as for "probably" being damaged by "low impact", that's absolutely contradicted by excellent fatigue characteristics. reaching to the ethereal "unknown" scare factor is just chicken little trying to be afraid and wanting to tell everybody else to be the same.

why don't you do the experiments i suggested?
.

Relevant Pages

  • Re: more cfrp bleating
    ... An interesting paper on the challenges presented in designing a crashworthy CF composite aircraft: ... application of composite materials to aircraft fuselages ... "Metals absorb energy by plastic deformation. ...
    (rec.bicycles.tech)
  • Other questions about the Airbus planes
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  • Re: "CF Bike Shatters" - continued
    ... expect to see composite aircraft structures being nondestructively ... method that is used in the aircraft industry for inspection during ... Hamilton Standard and I've seen it used by engineers and technicians ...
    (rec.bicycles.tech)
  • Re: "CF Bike Shatters" - continued
    ... Have you comported your life in such a manner that you would expect to see composite aircraft structures being nondestructively tested? ... method that is used in the aircraft industry for inspection during ... One from Aircraft Maintenance Technology ...
    (rec.bicycles.tech)
  • Re: ABS or Not ABS ...
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