MYP Design Composites and Smart Materials Notes

A Composite Is Two Materials Covering Each Other's Weakness

1. A composite joins two different materials so the pair performs better than either one alone.
2. The parts stay separate inside the material, so you can still see the fibres in a cut edge of glass fibre.
3. That separation is what makes a composite different from an alloy, where the ingredients melt together into one new metal.
4. Every composite has a reinforcement that carries the pulling forces and a matrix that surrounds it, holds it in shape and spreads the load between fibres.
   1. The matrix also protects the reinforcement from water, sunlight and knocks.

Four Composites, From a Canoe Hull to a Sheet of Plywood

1. GRP, glass reinforced plastic, is glass fibre matting soaked in polyester resin, and it builds boat hulls, canoes, water tanks and body kits.
   1. It is cheap, waterproof, moulds into curves a sheet material could never manage, and it can be repaired with more resin.
2. Carbon fibre sets woven carbon cloth in epoxy, giving a part stiffer and lighter than steel, which is why racing bikes and F1 bodywork use it.
   1. It costs many times more than GRP and it shatters rather than dents once it is overloaded.
3. Concrete is gravel and sand held in set cement, strong under squeezing but weak when pulled, so steel bars are cast inside it to take the pull.
4. Plywood is the simplest case you can hold: wood veneers are the reinforcement, glue is the matrix, and crossing the grain every layer removes the weak direction.
5. Repair and recycling are the shared weakness, because you cannot separate the reinforcement from the matrix once it has cured.

Fibre Direction Is a Design Decision, Not a Detail

1. A composite is strongest along the direction its fibres run, so laying them the wrong way wastes the material entirely.
2. Chopped strand mat points fibres randomly, giving equal but modest strength in all directions, which suits a curved hull.
3. Woven cloth points fibres two ways at once, and stacking layers at different angles builds strength wherever the load will come from.
4. A bike frame builder aligns fibres along the tube for pedalling loads and wraps them around it to resist twisting.
5. The same logic runs through plywood: crossing each veneer is fibre direction solved in the cheapest possible way.

Smart Materials React, So the Product Needs No Circuit

1. A smart material changes a property when its surroundings change, and changes back when they change again.
2. The reaction is built into the material, so it needs no sensor, no microcontroller and no battery to work.
3. That makes smart materials useful where a circuit would be too fragile, too expensive or too large.
4. The trade is control: a circuit can be reprogrammed, while a material always reacts at the same trigger point.
5. Modern materials sit nearby: they are new or improved materials such as polymorph or aerogel that do not react to anything, they are simply better at a job.

Four Smart and Modern Materials You Can Actually Buy

1. Shape memory alloy, usually nitinol, can be bent cold and snaps back to its remembered shape when warmed, often by hot water or a small current.
   1. Real uses include spectacle frames that survive being sat on, dental braces that keep pulling as they warm, and stents that open inside a blood vessel.
2. Thermochromic pigment changes colour at a set temperature, typically around 27 to 31 degrees Celsius, and fades back as it cools.
   1. It prints onto baby bath thermometers, kettle strips, beer can labels and mugs that reveal a pattern when filled.
3. Photochromic pigment darkens in ultraviolet light, which is how reaction lenses tint outdoors and how UV warning beads change colour in sunlight.
4. Polymorph is a modern thermoplastic that arrives as white granules and turns clear and mouldable in water at about 62 degrees Celsius.
   1. It sets to a tough nylon-like solid in a few minutes and can be reheated repeatedly, which makes it ideal for custom grips and quick prototype parts.
5. Electroluminescent wire glows evenly along its whole length when fed alternating current, stays cool, bends around corners and suits costumes, signage and safety trim.

Use a Smart Material Where It Solves a Real Problem

1. Ask what the material tells the user or does for them that a printed label could not.
2. Thermochromic pigment on a child's mug earns its place, because a young user who cannot read still gets a warning.
3. The same pigment sprayed on a pencil case is decoration, and a moderator will read it that way.
4. Check the trigger point matches your situation, since a pigment that switches at 31 degrees Celsius is useless as a warning for a 60 degree surface.
5. Cost and supply matter too: nitinol wire and EL wire both come from specialist suppliers and need lead time before a deadline.

Testing a Smart Material Fairly

1. Measure the actual trigger temperature with a thermometer rather than trusting the supplier's figure.
2. Run at least ten cycles and note whether the change gets weaker or slower.
3. Ask a user whether they noticed the change without being told to look for it, which is the only test that matters for a warning.