Hi all,
I wonder if someone faced the question related to the use of resin infusion, (not RTM) in aircraft primary structures and subsequent certification issues. This argument seems to be “hot”, due to the increasing interest in the out-of autoclave tecniques , and I would like to have your opinion/comment ( direct experience would be appreciated a lot…) about the subject.
What exactly is the question here? I deal with this on a daily basis.
Hi TET,
I wonder if resin infusion is still far from substitute autoclave tecniques for primary structures as spars, ribs, stringers ,panels.etc. for application in commercial aviation.
<I’m going to answer in general terms. As always there are exceptions.>
Infused parts are often heavier due to a higher resin content. Infusion resins need to have a low viscosity so have less cross linking than a prepreg resin, this combined with lower consolidation means less strength.
There can be issues with finding a flame retardant resin too, if that is needed. If you are going to hand mix the resin, you will need to ensure that ‘Bill’ does it right every time. I have a mate in the marine industry and on Monday’s they have issues with poorly measured and mixed resin.
A lot of the New Zealand aviation industry has a massive hard-on for infusion. But I know they are having issues with getting parts to work. We made a part in prepreg that weighed 20kg and passed all flight load tests first time and was flame retardant. The company we elsewhere and the part is now infused and weighs 40kg and took 12months to get it to pass the flight test and they have to paint it to get it FR.
However; I’m not anti infusion, I think of it as the spectator sport of composites as it’s great to watch one run. If you need the lightest, strongest parts use prepreg; if you need a light, strong part use infusion. it’s all about using the right tool for the job.
lol sounds like ‘Bill’ needs to drink a bit less on the weekends! Good job its only boats that carry people right… otherwise some one might get hurt :eek:
He also told me a story about a guy that showed up still drunk from the night before and fell asleep in a corner. Some of his mates thought it would be funny to wake him up by pouring 20kg of vinyl ester on him. And it’s a super yacht builder too.
well atleast the guy that fell asleep in the corner didnt mess anything up! apart from his hair trying to get the resin out! bit stupid to poor resin on him… apart from anything think of the waisted money! lol
Moke,
your first post is interesting, nevertheless the work made by some companies, like EADS with VAP system, seems to show that the method is not “so bad” for aviation.
Besides, we have to say that a serious comparison between the two methods is not available; maybe this is due to the slowness, driven by costs and safety issues, of aeronautical sector in considering manufacturing alternatives. But many accident of airplanes that use large quantities of composites, show that they happen indipendently by the technology used for composites ( mostly autoclave pre-preg) while are some details (consider joints for example ) that make the difference.
About weight…there are source that affirm that infusion gives fiber content near (but not) equal to pre-pregs, other sources affirming the contrary 
… but none makes the comparison using credible numbers.
Of course I’m not against pre-preg; these posts are aimed to investigate the margins existing for other manufacturing methods in aviation, infusion in this case; and only people directly involved in the sector know how things really are.
Like I said Wings, there are exceptions and infusion can be used to make aeroplane parts. I think since composites are only now getting wide spread use in aircraft there will be a shortage of comparisons for a little longer. 15 years ago no one would use a carbon mast on a super yacht, now no one would use anything but carbon. I know the University of Auckland is doing a lot of research on infusion in aerospace for Air New Zealand.
ask TET, his business makes airplane wings and probably both ways.
hasnt TET had a thread running previously about infusion and cores? im sure that he put a number of pics in that of aero parts that were being infused. wasnt that long ago maybe month and a half or so…
http://www.compositescentral.net/showthread.php?t=4243
Here is the thread that I was thinking of, wasnt quite as I remembered it! still a good thread and I think that these are aeroplane parts, infused. It is about infusing with core materials.
Of course I read the thread Matvd is referring to…very,very interesting ,as the most of TET’s threads.
I would like to ask TET: how much weight ( in percent) would be saved if the same panels were made using prep-preg ?
Primary and secondary flight structures are not the same things. You MUST have your primary structure perfect!!!
Now, there is still alot of work being done on making infusion flight worthy. Some people/processes have gotten it down to as good as prepreg in an autoclave. It all depends on what the part is, and what YOU can make!! It all has to pass qualifications in the end. If you can pass qualifications with a infused door, but not a frame, or wing box…then you make the parts as needed.
I have read on a few occasions a correct in fusion can be with in 5% of the weight as a pre preg.
It all depends on the prepreg and resin infusion materials used.
With the very open structure materials for RTM Light, a Vf (fiber volume) of 14-20% is common. They relatively high-weight parts are not suitable for flight, in general. (However, they are very useful in articles where prepreg and infusion are compared, and the aim is to show how bad infusion is.)
Infusion of multiaxial fabrics usually give me between 50 and 60% Vf. Prepregs will be even higher, if autoclaved, as the pressure is higher. However, the difference will not be that much. (at some point the fiberstack is about fully compressed. Pushing harder does not compress it further that much)
For undirectional 72 percent fiber volume fraction is the theoretical limit. After that perfectly circular fibers will be touching each other leading to a heavy drop in strength.