[SS-VehDev] Re: composite short stack/instrumentation section

[Lakestake Rocketry]

Hi Bob,

For the tapered joint: would it then use cement to hold the
two tapers together?

Matt

On 10/13/05, william colburn <space1space at sbcglobal.net> wrote:
>
> Excellent, all.
>
> A prime requirement and one that is not trivial is the
> ability to attach successfully with the same safety
> factor to the ends for closures. That is why I
> suggested a 40 inch length for the test piece. It can
> be hydrotested and then used, if we wish, for the
> short stack burn.
>
> Generally a single simple bolt circle is not going to
> do the job. Here are some solutions that have worked
> for others:
>
> Tapered joint- frequently seen on composite piping
> systems- the outer surface of the end fo the pipe is
> ground to a taper to fit the same taper on a fitting.
> The length of the taper is roughly one diameter of the
> pipe.
>
> Insert and bolt circle- The closure is inset a bit,
> perhaps 1/2 diameter and retained with an insert made
> from the same tubing by removing a strip
> longitudinally. The insert is held in place with epoxy
> and a complex bolt pattern of several circles.
>
> Pinned- seen on composite rocket motor cases- the
> closure is about 1/2 diameter in length. hundreds of
> small roll pins are used in holes which are drilled
> and then reamed for optimum bearing strength.
>
> Those techniques are used on unmodified composite
> filament wound tubing. If the ends are reinforced, we
> might get by with a lesser intense method. But we have
> to prove that early on as it is crucial to the success
> of the motor.
>
> BC
>
> --- Lakestake Rocketry <lakestake at gmail.com> wrote:
>
> > Thanks Colin,
> >
> > Great information.
> >
> > The whole airframe would not have to match the specs
> > for the motor casing,
> > at least the top half can be a lot lighter
> > construction.
> >
> > I was told (by my vendor) that uni was harder to get
> > and thus more
> > expensive.
> > That was several months ago. It sounds like either
> > that was *? or the
> > landscape has changed in the carbon supply world.
> > Good to hear.
> >
> > How do we figure a liner into your calculations? If
> > it has some mechanical
> > properties as well as providing insulation during
> > the second stage burn we
> > may be able to build a lighter motor casing.
> >
> > Richard, can your group recommend a liner for a
> > composite airframe
> > that we can use to refine our model?
> >
> > Colin, if you will be able to provide a wound tube
> > how would it compare
> > with the current fabric design in terms of weight at
> > the same strength?
> > Would you recommend that we use it as a motor casing
> > only with a light
> > fabric airframe over the top, or would it be both
> > the casing and aft
> > airframe which we attach the forward fabric airframe
> > and fins to?
> >
> > Matt
> >
> > On 10/13/05, Colin Hutchison
> > <colin at carboncopies.com.au> wrote:
> > >
> > > G'day all,
> > >
> > > Sorry for the delay. I've run some number on a
> > range of lay-ups. I
> > > guess it comes down to Margin Of Safety and how
> > close you would like to
> > > get
> > > to the limit. I've attached a screen grab of the
> > Excel spreadsheet I've
> > > been using. The ply count runs from 15 to 32
> > plies, however, the braided
> > > tube was modelled using two separate uni
> > directional plies. Therefore, for
> > > example, lay-up for ply count 29 is actually 5
> > layers of uni-directional
> > > and 12 layers of braid, totalling 17 layers. The
> > braid angle was also
> > > modelled at +-60deg instead of the optimum of
> > +-55deg. This makes the
> > > calcs a whole lot easier. I'll attach the complete
> > lay-ups at a later
> > > stage. Each ply (as seen in the calcs) is a 200gsm
> > layer of uni. So the
> > > braid would be equivalent to 400gsm.
> > >
> > > There are a few factors that affect all the calcs.
> > One of them being
> > > the breaking strain of the Carbon. I've done the
> > calcs for 4000us and
> > > 6000us. Typically Boeing use a value of around
> > 4000us. This allows for
> > > there own safety factors, one of them being holes
> > drilled in the
> > > surface. Another is the Young's Modulus of Carbon.
> > I've used a slightly
> > > reduced value from typical pre-preg so this should
> > be ok, but it comes
> > > back
> > > to my point that the supplier and quality of the
> > carbon does matter. Also
> > > the quality of the epoxy will affect the final
> > product.
> > >
> > > If you want to go to bare minimum the you could go
> > as low as ply count
> > > 17 (1 layers of uni and 8 layers of braid).
> > Allowing for 6000us then the
> > > minimum MOS is 0.1219. (Btw, the MOS is calculated
> > for each ply in the
> > > laminate and then the minimum value is the MOS
> > stated). The casing would
> > > come out at around 12.1lbs. If this were to be the
> > lay-up then I would
> > > probably recommend that the ends be beefed up a
> > little by adding more
> > > plies. Basically because you are going to be
> > drilling holes in it.
> > >
> > > I'll also just not here that the holes should be
> > at least 3 times the
> > > diameter of the hole to the edge of any composite.
> > >
> > > If you would like a little more safety, then ply
> > count 22 (2 layers of
> > > uni and 10 layers of braid) gives a MOS of 0.1637
> > at 4000us and weights
> > > 15.7lbs.
> > >
> > > If you can afford the few extra pounds (and I know
> > your pushing it)
> > > then I'd probably be going for something like the
> > 29 ply count. This gives
> > > a good MOS (nearly 1) and at the end of the day
> > will only weight 20.7lbs
> > > (41.4lbs for both stacks). If you were to swap
> > from metal to composite
> > > then you could probably afford the weight and
> > therefore little more
> > > safety.
> > >
> > > Each additional ply is approx 0.7lbs (so 1.4lbs
> > for the braid).
> > >
> > > So I guess what I need to know now is, how close
> > are you willing to cut
> > > it? I've also done the calcs for 1500psi and not
> > 1100psi, so the minimum
> > > MOS will probably be enough. If you like I can run
> > the numbers for 1100psi
> > > with a required MOS.
> > >
> > > Probably not the right spot to ask here, but what
> > is the final grain
> > > structure? Will it have a cylindrical core or star
> > shape etc?
> > >
> > > I still haven't found out about the filament
> > winding, but I will
> > > hopefully soon.
> > >
> > > >I have added up to four layers at a time to a
> > composite tube without
> > > bubbling
> > > >or wrinkling. Under what circumstances do you
> > find this a problem?
> > >
> > > Laying up more layers than that and vac-bagging.
> > Basically the plies have
> > > excess length and can't go anywhere and so they
> > end up buckling and
> > > causing
> > > wrinkles.
> > >
> > >
> > > >For the amount of fiber we'll need for this
> > project we should consider a
> > > >different source. I think that Roman may have
> > good suggestions along
> > > >these lines. If you (Colin) or any other team
> > member has a thought please
> > > >pipe up!
> > > >
> > > >Once we have a weave proposal everyone can start
> > keeping their eyes out
> > > >for availability of those grades/weaves at their
> > local haunts.
> > >
> > > I can get the stuff but unfortunately I have to
> > pay for it.
> > >
> > >
> > > >I assume that we want to use this sparingly due
> > to price.
> > >
> > > Not really. Carbon is basically sold by weight so
> > it shouldn't matter what
> > > form it's in (unless you get down to fine weaves
> > or really heavy
> > > weaves). Uni-directional should be the same price
> > if not a little lower
> > > that woven cloth.
> > >
> > >
> > > >The braided tube works well, I worry about being
> > able to find
> > > >the 'right size'. I have had to stretch the tube
> > I get quite a bit to
> > > >match the
> > > >size of project I am working on. It still works
> > well, you just don't get
> > > >'optimum'
> > > >performance as you noted.
> > >
> > > I know you can get it made up to specific sizes
> > but then you are stuck
> > > buying a fairly large quantity. I'll figure out
> > what size the braid needs
> > > to be to fit a 10in tube and sit at 55-60deg.
> >
> === message truncated ===
>
>
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