Roman

Fibreglass, Carbon Fibre, Paper Mache - The composites chat thread

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I have nothing to add to this thread, except that i like seeing what others are doing. A+ work, will keep reading.

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29 minutes ago, NickJ said:

Would love to share what we do in pictures, sadly i'd lose my job! 

We design/build alot of composite parts for the cryogenic industry, while they're often simple to look at, some of the materials used have interesting properties as to not tear apart from differential contraction and what not at 4K

You doing stuff for rocket lab?

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37 minutes ago, flyingbrick said:

You doing stuff for rocket lab?

Nah, but large part of me hopes they will sub some kind of design work to us, can only hope to have my scribblings in space!

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23 hours ago, Roman said:

God damn I really just didnt need to watch that infusion / vaccum bagging tutorial on making that bonnet. 

Holy shit that was awesome! 

 

Have you watched the pattern making / prepreg vids yet as they are just as good.

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I've watched the easy composites videos myself and it looks like they will ship prepreg to your door (they're in the UK), think the stuff has about a months shelf life once thawed.

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Yeah i have watched a vew vids on DIY ovens- prepreg just seems so quick, easy and clean. I'd love to use it on my intake plenum.

Does anyone here use a vacuum pump? I hear fridge pumps work extremely well.

 

Edit.

Waiting for all the sick bastards to say they use theirs every night.

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5a8dfaa427d2b_20phromyacal2regionIII-5.thumb.jpg.a556b51e3f9860951d158f83a607f98e.jpg

The above is for a product with small particle calcium carbonate filler at 20 phr by weight.

Looks like damage from short beam (primarily shear stress) loading is in the form of matrx-fibre interface debonding. Areas with low glass content seem to be the initiating sites for the damage, indicating that differential strains between these regions are responsible for the failure.

Item of note: Increasing glass content seems to decrease short beam strength, as the cracks in the matrix don't need to jump so far between fibers. I'm not sure at which point removing fibers will have little/negative effect on the short beam properties.

Therefore an ideal composite should have fairly uniform distribution of fibers to minimize the differential strains between neighbouring areas and too high of a glass content will cause reduction in short beam strength.

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5a8dfcf825c30_20phromyacal2regionI-1.thumb.jpg.f6a333b65169d9d8203def1e5ae07270.jpg

This image was taken from a sample loaded to the onset of nonlinearity. (Initial stages of short beam failure)

The big chunk is just a piece of silica, most likely from the sanding process.

The damage looks like it is the same mechanism as in late stages of failure (previous post), so I'd say that the section imaged in the previous post was probably early stage damage and I'll need to look for some later stage damage.

 

5a8dfdc07688a_20phromyacal2regionI-2.thumb.jpg.4fc7b677d2902420e025f32eb86d16f7.jpg

 

This image is a bit more zoomed in than the other one, same area. You can clearly see the filler particles. Right in the middle of the image you can see a microvoid caused by the filler particles agglomerating and excluding resin. It's interesting to note that there is no failure visible at this point, I would have expected the microvoids to be more likely failure initiation points than debonding. I guess that could be due to the fact that these voids are tiny, whereas the fibres are long enough that significant shear stress can build up along their length.

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5a8dfe96b5360_20phromyacal2regionII-1.thumb.jpg.5ff29e9b577c58372bf1e9929e268afd.jpg

 

This image was taken just after peak load was achieved on a sample. Looks like it is really falling apart at this point, you can see a bit of debonding and cracking on almost every fiber interface. It's interesting to see how quite a few of the fibers themselves are cracked, I'm not sure if this is due to the polishing operation or the loading process. All of the samples were polished at the same time using the same method so I would assume that if it was a polishing issue it would be present in more of the images.

It looks like this is a fairly filler-rich region of the product, which could explain the extent of the damage as the filler particles are probably acting as crack initiation sites.

The glass content is relatively uniform at this location, this could also explain the different failure mode. I think this sample withstood close to 3.3 kN before failure while the other two failed closer to 3 kN.

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What kind of camera or scanner or whatever is taking pics? 

Awesome detail on such a small cross section! 

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Also, although you can say "More uniformity of fibres makes it stronger" is  there realistically any process by which that's possible to achieve? 

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1 hour ago, ajg193 said:

5a8dfe96b5360_20phromyacal2regionII-1.thumb.jpg.5ff29e9b577c58372bf1e9929e268afd.jpg

 

So the round things are glass fibres? And the picture is a close up of a cut and polished section?  What is the application of the thing you are testing?

Excuse my ignorance/ noob questions

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14 minutes ago, cletus said:

So the round things are glass fibres? And the picture is a close up of a cut and polished section?  What is the application of the thing you are testing?

Excuse my ignorance/ noob questions

Yep the round things are individual glass fibers. While granule bits are calcium carbonate powder.

The sample is an 11x4 mm rectangle section bar which was tested under short beam loading conditions as in the image below:

IMG_0309.thumb.JPG.b0a0e42b2a2a9dd0ecf1f1363fd0f0a4.JPG

The top loading nose pushes down until a total displacement of 2 mm and the force and displacement are recorded.

The following graph contains the data from 10 such tests
5a8e1d1348e6f_shortbeamresponse.png.424116e25d6db6cb39b18fdb967afbda.png

 

The graph can be split into three distinct sections, linear response (up to about 0.6 mm),  initial damage (between 0.6 mm and about 1 mm) and damage growth (after 1 mm).

By taking a sample where the test was stopped at the end of each section and cutting it through where the central load is applied and then mounting it in acrylic and polishing it and then putting it through the electron microscope you can get some idea of what damage occurs at what point and what is causing the damage.

I've been exploring the effects of filler types and sizes on the mechanical and processing properties in pultruded products, these tests allow for reasonably quick and reliable comparisons between different recipes to determine what works best (or is the best balance between cheap and high quality, or ease of manufacture and quality etc).

The glass fibers are about 1/5th the diameter of the average human hair.


Here's a tensile test outcome (3.2 mm diameter rod, failure load about 1.1 tonnes):
IMG_0048.thumb.JPG.08ebbabc8ef08e9187fe9a33c14d1d34.JPG

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1 minute ago, NickJ said:

Or were you having pizza for lunch?

You got me. My favourite pizza is Sandlovers.

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