MYP Design Selecting and Testing Materials Notes

Start From the Specification, Not From the Materials Cupboard

1. Picking a material before writing a specification means you are choosing a favourite and then reasoning backwards.
2. Take each specification point and turn it into the property it demands, so must not tip over becomes needs a dense base.
3. Must survive daily use in a school bag becomes needs toughness and scratch resistance, two properties you can test.
4. A point that will not translate into a property is usually too vague to be worth keeping.
5. Then rank the properties, because the material that wins on your top two matters more than the one that scores an average across six.

Four Factors Decide Alongside the Properties

1. Cost is the whole cost, so count wastage, the finish you will need and any specialist fixings, not just the price of the sheet.
   1. A material that comes only in a 2440 mm by 1220 mm sheet is expensive for one small part, whatever the price per square metre says.
2. Availability is about your deadline: a material that ships in three weeks is the wrong material for a four week project.
   1. Check the sizes and thicknesses actually stocked, because 4 mm acrylic is common and 4.5 mm is not.
3. Workability is whether you can cut, shape, join and finish it with the tools and skills in your workshop.
   1. Aluminium is a fine material and a poor choice if the join you designed needs welding equipment your school does not have.
4. Environmental impact covers where the material came from, how far it travelled, how much energy it took to make, and what happens to it at the end.
   1. FSC timber, recycled aluminium and single-polymer products are all defensible answers; a mixed composite glued to a metal frame is not.

Workshop Tests Are Rough, and Rough Is Enough

1. You are not measuring an absolute figure, you are ranking three candidates against each other under the same conditions.
2. For hardness, drop a steel ball from a fixed height onto each sample and measure the dent, or scratch each with the same nail under the same finger pressure.
   1. Ranking by which material scratches which is a genuine test, and it is how the Mohs scale works.
3. For strength, clamp equal strips in a vice with the same length sticking out and hang masses from the free end until each bends or breaks.
   1. Record the mass at first visible bend as well as at failure, since a shelf that sags has already failed its user.
4. For absorbency, weigh a dry sample, soak it for a fixed 10 minutes, shake off the surface water and weigh it again.
   1. The gain as a percentage of the dry mass lets you compare samples of different sizes fairly.
5. For toughness, drop each sample from the same height onto the same floor and photograph what happens to the edges.

A Fair Test Changes One Thing and Nothing Else

1. The only thing that should differ between samples is the material, so cut every sample to the same size from the same source.
2. Keep the drop height, clamp length, soak time and loading position identical, and write those numbers down before you start.
3. Thickness is the trap: 3 mm acrylic against 6 mm plywood tests thickness, not material.
4. Repeat each test three times and take the middle result, because one unlucky sample with a knot or a scratch will mislead you.
5. Say what you could not control, such as a chipped edge from cutting, since naming a limitation is worth more than pretending it was perfect.

Recording Results Is Where the Marks Live

1. Record the conditions once above the table, since a result with no method behind it cannot be judged or repeated.
2. Photograph the samples before and after, in the same position and lighting, with a ruler for scale.
3. Finish with a sentence that names the winner and the specification point it satisfies, not just the highest number.
4. Keep the tested samples, because a moderator seeing a labelled bag of broken strips knows the testing was real.
5. Build one table with materials down the side and tests across the top, so a reader compares in seconds.

The Best Material Is the One That Loses Least

1. No material passes every test, so the decision is about which compromise your user will notice least.
2. Plywood may be stronger than acrylic while acrylic is the only one that ignores water, and the right answer depends on where the product lives.
3. Write the trade-off down in your own words, because a designer who names what they gave up shows better judgement than one who claims a perfect choice.
4. Different parts of one product can take different answers, such as a plywood body with an acrylic window.

Testing Prototypes as Well as Samples

1. A sample tells you about the material, while a prototype tells you whether the shape and joints survive too.
2. Test the prototype the way a real user would, then note where it failed first, since that spot is where your next design change goes.
3. Ask a real user to handle it before you decide the material is settled, because comfort and grip never show up in a bending test.