1. UNIT 2: Physical Properties of Metals Unit 2 Copyright © 2012. MDIS. All rights reserved. 1 Manufacturing Engineering

2. Objectives Enumerate and explain the main properties of importance in metals Understand the behaviour of metals under various conditions Relate to the use of certain metals for given applications 2Unit 2 Copyright © 2012. MDIS. All rights reserved.

3. Types of Materials Solids Liquids and Gases Metals are predominantly Solids Properties of interest: density, melting point and specific heat 3Unit 2 Copyright © 2012. MDIS. All rights reserved.

4. Commonly used Properties Density “the concentration of matter in a region of space” ρ = Mass / Volume its unit in SI is kg/m 3 less dense metal will be lighter than a denser metal. E.g.: Aluminium is lighter than steel Automotive sector makes great use of Aluminium -higher mileage Aviation industry needs very tough but very light metals- Titanium and its alloys 4Unit 2 Copyright © 2012. MDIS. All rights reserved.

5. Melting Point -melting and boiling points of ice / and water are 0Ċ and 100Ċ - cast iron will melt into liquid at 2150F (1176C); lead at 621F(327C) -one cannot use lead in the creation of a ladle for a steel furnace; cannot use steel as a soldering wire as it will simply not melt 5Unit 2 Copyright © 2012. MDIS. All rights reserved.

6. Specific Heat “the heat needed to raise the temperature of a kg of substance by one degree K” the heat needed to change the temperature of a given amount of substance sand soak up much more heat than metals, before their temperature rises significantly insulate heated objects, we would need materials with high specific heat to keep an object cool, it is advisable to use a low specific heat material. 6Unit 2 Copyright © 2012. MDIS. All rights reserved.

7. Thermal Conductivity and Expansion a measure f the materials ability to rise in temperature as it is postioned next to an object of high temperature As the temperature of the source object rises, the thermal agitation of the materials molecules causes the energy to propagate through the material quickly for metals. This is called high thermal conductivity. high conductivity- necessary to heat up and cool down components of an electronic circuit A refrigerator door is lined with insulating foam on the inside to keep the outside high temperatures from seeping heat into the cooled space within 7Unit 2 Copyright © 2012. MDIS. All rights reserved.

8. Unit 2 Copyright © 2012. MDIS. All rights reserved. 8 http://en.wikipedia.org/wiki/Thermal_condu ctivity#Experimental_values

9. Electrical Properties Resistance: It is a measure of the ability of a material to offer resistance to the flow of a current It is what causes resistance in a material Dielectric Strength: This property of a material determines how well a material can withstand the application of high voltage 9Unit 2 Copyright © 2012. MDIS. All rights reserved.

10. Magnetic Properties Diamagnetic (repulsed by magnetism) Paramagnetic (attracted by magnetism) or Ferromagnetic (become permanent magnets themselves) Electromagnets are created by using electric current in coils to create magnets CAT scanners are made of huge magnets that cause magnetic response in biological tissues which are then mapped back into images 10Unit 2 Copyright © 2012. MDIS. All rights reserved.

11. 11Unit 2 Copyright © 2012. MDIS. All rights reserved. Optical Properties Transmissivity -how well light can travel through a material reflectance -how well a material reflects oncoming radiation absorbance -how much of the oncoming radiation is captured by the material within itself

12. Corrosion Resistance As we know Iron rusts very quickly in presence of humidity alloys of steel that do not rust even in the most corrosive environments. Tensile strength The ability of a material to withstand tensile stress - Industry normally uses the elastic limit, but the Ultimate strength is also used in designing Unit 2 Copyright © 2012. MDIS. All rights reserved. 12

13. Torsion and Bending strength torsion strength of a material is the maximum applicable torsion stress bending is subjecting a member of a structure to a bending moment that induces tensile and compressive forces in its cross-section that may cause failure Hardness property of a material that resists indentation on its surface higher hardness materials are capable of wearing out the softer materials Unit 2 Copyright © 2012. MDIS. All rights reserved. 13

14. Fatigue failure occurs in components that are subjected to cyclic variation of stresses- aircraft wing struts, pistons, crankshafts, etc continuously suffer forces in opposing directions in a rhythmic pattern can cause components to fail at a fraction of its real tensile strength Creep creep failure happens in situations where forces involved cause less than the limiting stresses on components. the premature deformation of materials at stress levels that are otherwise safe, but in elevated temperature conditions Unit 2 Copyright © 2012. MDIS. All rights reserved. 14

15. Impact strength the ability of a material to sustain a standard impact in the impact test- standard test is the Izod Impact test with a notched or without a notched specimen Unit 2 Copyright © 2012. MDIS. All rights reserved. 15