ANISOTROPIC COMPOSITES

I have a fair amount of experience in the design and manufacture of composites from my Undergraduate Masters project, and so this week I decided to experiment with the anisotropic deflection behaviour of composties by weaving my own fibre structures and making some bespoke fibre shapes.

A QUICK INTRO TO COMPOSITES MATERIAL SCIENCE

• Isotropy means uniformity in all directions. In relation to materials, it means a uniform (or as close to as possible) material structure, e.g. metals. In an isotropic composite, all the fibres or particles must be randomly oriented throughout the resin to create this same uniform material structure. It is this uniformity which makes isotropic materials easier to predict their behaviour when exposed to different loads, e.g. the simple narrowing of the width of a piece of material when under tension (Possion's ratio)
• Anisotropic materials do not have a uniform material structure, and as such do not have as uniform a reaction to loads. Most composite materials react in an anisotropic way to some extent due to the very nature of their heterogeneous material structure. In fact the design of a composite material, especially the shape and interaction of the fibres contained in the resin matrix, can be tailored to certain forces and made to deflect in a specified way, which can be very different to the way an isotropic equivalent material would do, e.g opposite to the example above, a material can be made to increase in width as well as length when under tension (auxetic composites)

HOW TO MAKE WOVEN COMPOSITES

HOW TO MAKE ANISOTROPIC FIBRE COMPOSITES

 1: CREATING FIBRE PATTERNS I wanted to experiment even more with creating different deflection behaviours, so I created bespoke fibre patterns from wire and cast these in polyurethane rubber The fibre structure on the left should create a bulge in the centre when the sample is in tension, as the convex shape of the fibres will straighten and come together, compressing the central section of the rubber The fibre structure on the right should create a curved shape in tension, as the distribution of fibres means that the right edge of the sample is less supported in tension and will stretch more than the left side 2: THE RESULT