16. Properties of Materials 16. Properties of Materials Working Properties Toughness ● The ability of a material to resist the propagation of cracks. ● It is important where abrasion and cutting may take place. ● Design contexts include automobile bumpers or any design context where impact is likely. Ductility The ductility of a material can be defined as, ‘the ability of a material to change shape (deform) usually by stretching along its length’. Elasticity (Elastic region) ● When material is bent (not reaching yield point) then relaxed, it reaches original position again. ● When a material behaves elastically, when the stress on the material is released before it breaks, the extension (strain) relaxes and the material returns to its original length or shape. ● If you squash a drinking Why does material choice matter so much? Materials are often developed by materials engineers to have specific properties. The development of new materials allows designers to create new products, which solve old problems in new ways. For example, the explosion of plastic materials following the second world war enabled products to be made without using valuable metals. Malleability The malleability of a material can be defined as, ‘the ability of a material to be reshaped in all directions without cracking’ 16. Properties of Materials Physical Properties Density ● Is the mass per unit volume of a material. ● It’s importance is in portability in terms of a product’s weight and size. ● Design contexts include: ● pre-packaged food (instant noodles) is sold by weight and volume, ● packaging foams/material ● any other context where weight and volume are important. Thermal conductivity ● A measure of how fast heat is conducted through a slab of material with a given temperature difference across the slab. ● It is important for objects that will be heated or must conduct or be insulated against heat gain or loss. Electrical Conductivity ● Is the measure of a material’s ability to conduct or resist electricity. ● It is important when selecting materials as conductors or insulators ● Design contexts include, electrical plugs. 16. Properties of Materials Smarter Materials... Photochromicity ● Photochromicity refers to a material that can described as having a reversible change of colour when exposed to light. ● A chemical either on the surface of the lens or embedded within the glass reacts to ultraviolet light, which causes it to change form and therefore its light absorption spectra. ● Design contexts include: One of the most popular applications is for colour-changing sunglass lenses, which can darken as the sun brightens. Shape memory ● Shape memory alloys (SMA) are metals that exhibit pseudo-elasticity and shape memory effect due to rearrangement of the molecules in the material. ● Pseudo-elasticity occurs without a change in temperature. The load on the SMA causes molecular rearrangement, which reverses when the load is decreased and the material springs back to its original shape. The shape memory effect allows severe deformation of a material, which can then be returned to its original shape by heating it. ● Design contexts include frames of glasses, medical tools and antennas for mobile phones. 16. Properties of Materials Putting Materials to the Test... Compressive strength ● The ability of a material to withstand ‘squashing’ forces. ● Design contexts include: ceramic floor tiles, concrete and bricks for buildings or anything that requires to bear weight. Tensile strength ● The ability of a material to withstand pulling (apart) forces. ● It is important in selecting materials to resist stretching. ● Design contexts include, ropes (climbing or towing), cables (in elevators) and fishing lines. 16. Properties of Materials Something Extra..