Re: Ballistic containment

Ian <Ian@xxxxxxxxxxxxxxxxxxxxxxxx> wrote in
news:1$cqSKAgSr1DFwr9@xxxxxxxxxxxxxxx:

> Hello
>
> My interest is in the subject of light hovercraft. Recently the
> subject of guarding of thrust propellers has become important.
>
> Most hovercraft use axial fans or propellers to provide thrust, and
> these are normally contained within a guard or duct. There is the need
> to be able to show that a particular guard construction is capable of
> containing a failed blade of known kinetic energy.
>
> Guards are usually constructed of GRP or wire mesh, and are sometimes
> reinforced with kevlar. Typical blade kinetic energies are in the
> region of 2000J - 3000J.
>
> Since many craft, and therefore guards, are one-offs built by
> amateurs, there is the need to provide a means to calculate, or
> otherwise verify, the capability of a guard to contain the given KE.
> This appears to be somewhat of a problem!
>
> Can anyone suggest any means to verify guard capability without
> resorting to potentially expensive ballistic testing?
>
> References to prior work, calculation methods?
>
> Or references to ballistic containment materials that can be supplied
> with proven performance to contain 'x' J from which a guard may be
> constructed?

One approach would be to work out the work involved in a fully plastic,
hinged, deformation, of the guard. In theory, because it uses an assumed
mechanism, it provides an upper bound to the energy absorbed, but by
using a parametric model, and differentiating, you should be able to
find a reasonable limit.

Given the popularity of this field, perhaps it would be better to define
an overstrength solution and make that the legal minimum.


Cheers

Greg Lo***

.

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