Vacuum Bag Moulding

[chrisegan85]

Hello all I am new to this forum.

I have been having problems with a project as part of my studies. Your help would be greatly appreciated on this.

I am to produce composite samples (Polymer-matrix composite) using vacuum bag moulding. I have looked into the process and understand how it works and have also got the necessary materials on order but not that sure if its going to be so easy to produce the samples. Any advice/tips on this process would be great???

Also info on producing the lay-up prior to the vacuum bag moulding would be great.

The next question I have is that I will be tensile testing the samples using an instron. I will then be comparing these results to theoretical results. I am unsure about the calculations used to calculate these theoretical results for comparison. Please please help me with this as I am lost and my supervisor on this project has been useless.

I will be producing samples varying the resin used (polyester and epoxy) as well as varying the orientation of he fibres. The woven fibre will be aligned to the direction of loading and also some samples the fibres will be aligned at 45 degrees to the direction of loading. I will also be using chopped strand matting.

Hope this is not too long and that someone can help me on this.

Chris

 

[tomotomotomo]

Hi chris,

You should start by reading up on the Voigt and Reuss models, also refered to as the Isostrain and Isostress models, respectively.

Providing that you have the elastic modulus of both the matrix material (epoxy or polyester) and fibre material (carbon, glass etc.) these forumulae allow you to calculate the theoretical elastic modulus of the composite as a whole,
and also calculate density and the elastic limit of the composite.
Isostrain is used when the force is orientated parallel to the fibre direction (as in your experiment), and Isostress is used when the force is perpendicular.

you say you're using chopped strand matting.
I'm unsure of what sized particles/strands you'll use, but according to my notes if you randomly orientate the small fibres, the resulting composite will have an isotropic fracture toughness (imagine MDF compared to natural wood).
if you are modelling an isotropic composite, the resulting elastic modulus is roughly an average of the isostress and isostrain models.

I really hope this helps as a starting point, i've tried to be as accurate as I can but still read some text books as well to gain a deeper understanding.

all the best
James

 

[MechanicalChef]

If you know ths basics, and have the basic materials coming, great. Based on your descriptions, I'll assume you're working with fiber-glass.

Proper wet-out prior to bagging will be the most crucial step. Make sure you have ordered a slotted/paddle roller or two. (fiberglast sells these items)