Physical Characteristics and Material Properties
For your exam and coursework you need to be able to confidently talk about the properties of materials. You need to be able to describe how something is using technical terms. For instance you might want to say you are choosing copper because you need a good conductor of heat.
Properties are also called characteristics.
Strength: How much weight a material can put up with without snapping, bending or compressing. Particularly important when designing structures.
Absorbency: How much liquid can a material soak up? Natural fibres are much more absorbent than synthetic fibres. A paper towel is more absorbent than a swimming costume.
Density: This is the mass per unit volume. Put simply it is how heavy and solid something is. For instance a plastic garden chair is less dense than a metal garden chair.
Fusibility: The ease at which two pieces can be joined together. Solder has a lower melting point than other metals so can be used to fuse them together.
Electrical conductivity: Good conductors allow electricity to pass through them without loosing power. Poor conductors are called insulators. Metal is a good conductor, plastic is a good insulator which is why electrical wiring is covered in plastic.
Thermal conductivity: This is how well heat travels through a material. Pans are good thermal conductors to heat food efficiently whilst their handles are poor thermal conductors so you don’t burn your hands.
Hardness: How well a product withstands scratching, abrasion and denting. Tools strength steel is hard to withstand drilling and cutting other materials.
Toughness: A tough material is hard to break but can still change shape. Kevlar in a bullet proof vest is tough and flexible.
Malleability: Materials that are soft enough to shape are malleable. Sheet metal is malleable as it can be formed into shapes, through cutting and bending.
Ductility – Materials that can be stretched into a long length like wire.
Elasticity – How much stretch something has and is still able to return to its shape. A pair of tights has high elasticity.
Magnetism - Whether a material is magnetic or not can be useful for many reasons, to create a switch, pick something up or release it or generate power. Magnetism is useful in motors, generators and speakers.
Flexibility - The ability of a material to bend, fold and curve. A sheet of polythene, for example, is very flexible.
Printability - Is the ability of a surface to take ink. Paper is the obvious example.
Biodegradability - How soon and how easily can a material biodegrade? Organic materials biodegrade much easier than oil based materials.
Material properties are often combined to fulfil a need:
Polycotton: Easy to clean, creases less than cotton and can be dyed which polyester on its own can’t.
Brass: Copper, which is a good conductor, is mixed with zinc which resists corrosion.
You may get asked in your exam to explain the meaning of some properties or give some examples of materials with certain properties. You should also use the technical terms when labelling your designs for extra marks by showing your deeper understanding of a material and your ability to make informed choices.
Modifications of properties:
Some products are modified to add protection or fix a common problem to keep quality high.
Flame retardant spray - Legally soft furnishings and nightwear have to be resistant to fire. They are sprayed with a flame retardant spray.
Flame proof fibres – Racing drivers and fire fighters require lightweight, cool fabrics (such as cotton) but have flame retardant fibres woven into the fabric.
Anti stain – Additives such as silicone and Teflon can make fabric resistant to stains. This is often seen in school uniforms which need to be hard wearing.
Moisture resistance – Mildew is a sort of mould which can cause fabrics to rot, it thrives in damp conditions. A spray can be added to make a product damp resistant.
Paper and board:
Additives to help ink dry – To help speed up the rate of printing an additive can be put into ink to help it dry quicker so stacks of printing can be produced without sticking or smearing print.
Varnish – A top coat of thin varnish on paper or card will create a shiny smooth finish and give it some protection from moisture.
UV varnish – Gives the same protection as varnish but can be applied to spots of paper giving a shiny finish or the whole sheet. It is set with an Ultra violet light. It is particularly useful on paper which will be handled a lot.
Timber and board:
Seasoning – Wood that has been cut down is full of moisture and will rot and warp if used straight away. Once stripped of its bark and sliced it has to be stored dry and flat. Beams used for building need to also be pre stressed to avoid any bending or warping.
Tanalising – Outdoor wood needs tantalising to prevent rot. Once seasoned it is dipped in a tank of preservative with the air removed to force the preservative into the grain as deep as possible. It is then dried and ready to use. This will prevent rot and insect damage.
Varnish, wax and paint – To create a smooth finish and protective layer you can coat your wood. Varnish and wax are see through so keep the grain of the wood visible, paint covers the wood completely. As long as the rough grain is sanded between layers you can make a smooth protective finish.
Annealing – Heating a metal and allowing it to cool slowly makes a metal ductile and easier to bend without snapping.
Dip coating – Heating the metal and dipping it into plastic grains which melt to a smooth finish around it creates a comfortable and less thermo conductive handle.
Galvanising – Because ferrous metals rust easily it is galvanised by giving it a protective layer of zinc.
Photosensitive PCB board has the surface anodised with aluminium to improve the surface hardness.
Composite materials can provide protection to electronic components, used in phone cases.
Polymers used in casings can be ribbed for strengthening.
Ultra violet light (daylight) can damage the structure to polymers. Whilst liquid a UV stabilising chemical can be added to stop the degradation. Particularly used in outdoor furniture.
Triangulating the edge of polymer rod can increase its strength.