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

[Richard Nakka]

Colin,
Excellent work, I applaud your efforts. I'll take a closer look at the 
table you provided in a bit, but it appears to be a promising approach 
to investigate further.
One thing I must point out right off is that the casing mass is 
critical. Just how critical?
We've currently targeted 78 lbs  (35 kg) for the two casings that make 
up the dual-phase motor, total length 240 inches.

http://sugarshot.org/downloads/config_dph47.gif

This cuts down the list to the first 5 or so. However, we would like a 
margin of safety of at least 0.50 (1.5 safety factor)., so things get 
kinda dicey. We may have to take a closer look at the 6000 us  allowable 
(Boeing is known to be particularly conservative. As well, their 
criteria take into account damage tolerance & a 20 year life).

More later,
Richard




Colin Hutchison 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.
>
>
>> Just adding a few more layers makes sense, but since this is an 
>> international
>> project we may have to ship the part cross-country for testing.
>
>
> You could probably do the tests yourself.  Basically if you have the 
> ring that has been cut off the end of the casing, all you have to do 
> is sit it upright and put a load on it.  When you squeeze the ring the 
> sides will deflect outwards a given amount.  If you can measure the 
> load and the displacement of the sides then I can work out the actual 
> material properties.  So there should be no need to send it cross 
> country.  I'd also need to know the dimensions of the ring.
>
>
> Colin.
> ------------------------------------------------------------------------
>

-------------- next part --------------
Skipped content of type multipart/related