Institute of Applied Technology

1. Institute of Applied Technology Year 11 Engineering Materials Semester 1 October 2011

2. Engineering materials Module 2: Properties of Materials

3. Objectives After the completion of this unit, you will be able to: • evaluate the use of certain materials in engineering applications based on their properties. • differentiate between mechanical and technological properties of materials. • identify and explain different mechanical properties. • differentiate between tensile, compression and shear stresses. • compare some properties of metals using simple workshop tests. • explain the technological properties required for material processing.

4. Introduction • Manufacturing is defined as the activities performed to convert “stuff” into “things”. • Successful products begin with appropriate materials. • You wouldn’t build an airplane out of lead or an automobile out of concrete. (Why?) • When selecting a material for a product or application, it is important to ensure that its properties will be adequate for the expected operating condition.

5. Mechanical properties Reaction is to break Action is to hit • An action is to do something, like to hit or to push. A reaction is whathappens to the thing that is being hit or pushed. • A mechanical property tells us how a material reacts to an action. • If you hit glass It will break. The action is to hit, the reaction is to break. What do we call this reaction? • We call this reaction the mechanical property of brittleness. A hammer hitting a glass window

6. Mechanical properties • The mechanical properties that we study in this module are: 1) Mechanical strength. 2) Elasticity. 3) Plasticity. 4) Malleability. 5) Ductility. 6) Brittleness. 7) Hardness. 8) Toughness.

7. 1.Mechanical strength • Strengthis the ability of a material to resist the actions of a mechanical force. • Materials used in mechanical engineering must have strength to resist mechanical forces, which will try to break, bend, deform or wearthem. The three ways in which a force can be applied to a material are: • Tensile force. • Compressive force. • Shear force.

8. A. Tension Tensile force • Tensile force is a pulling force . • A car tow rope needs tensile strength or it will break when pulled. The material of the rope is in tension. Car rope under tension Tensile force is a pulling force

9. B. Compression • A compressive force is a pushing force . • The engine connecting rod needs the property of compressive strength when it is pushedby the piston to turn the crankshaft. The material of the connecting rod is in compression. compressive force Anengine connecting rod under compression

10. C. Shear • Shear force is a cuttingforce . • Rivets need shear strength to resist being cutby a shear force. The material of the rivet is in shear. Shear force Sheet Metal Shearing Machine Rivet under shear

11. 2. Elasticity • Elasticity is the ability of a material to absorb force and bend in different directions and then returning to its original position after removing the force being applied. • Elasticity is the reaction in the material to a force. • The opposite of elasticity is plasticity An elastic spring An elastic string

12. 3. Plasticity • Plasticity is the ability of a material to absorb force and change in shape permanently after removing the force being applied. • Plasticity is needed when we bend or pull metals (ductility) and when we compress metals (malleability). Manufacturing of a sheet metal from a thicker piece of metal.

13. 4. Malleability • Malleability is the property that enables a material to be reshaped by compressive forces in all directions without cracking. • Malleability is needed when shaping and forming materials with a compressive or pushing force. The compressive force will plastically deform a malleable material. • The malleability of some materials is improved by heating. The formation of the rivet head The blacksmith is heating the steel to improve its malleability

14. Malleability • To compare the malleability of two • metals we can take two similar test • pieces made from different metals • and hammer them to reduce their • thickness until they start cracking, • we can compare how much each • metal has reduced in thickness • without fracture. • In Fig. 2.13 which of the two test • pieces has the highest malleability • A or B? • ………………………………………………….

15. Malleability Practical Task 1: Compare test pieces made from different materials such as copper, brass, aluminum and steel and place them in order of malleability in the table below. Use a hammer to help you make the comparison.

16. 5. Ductility • Ductility is the ability of a material to be stretched into shape along its length. • Many ductile metals are also malleable, but malleable metals are not always ductile. Both ductile and malleable metals have high plasticity. • Some materials like ceramics and castiron have no ductility and cannot be formed by bending, pulling or drawing forces. • Gold is considered to be the most ductile material. • The opposite of ductility is brittleness. A ductile material under tension Ductility is needed to draw a wire

17. 6. Brittleness • Material is brittle if it has little ability to deform (change shape) before fracture. • Brittleness is a problem in engineering, as most of the time we do not want things to break easily. • Brittleness comes into things when we make them hard. Many hard materials are brittle. White cast iron and glass are good examples of brittle material. A brittle material under impact energy

18. 7. Hardness • Hardness is the ability of a material to resist scratching, wear and indentation. • Cutting and marking tools need to be harder than the materials they mark or cut. • If we scratch or file copper, brass, steel and aluminum using an engineer's file we can compare how easy or difficult it is to remove metal from each of these materials. A scriber The scriber should be harder than the steel to mark it

19. Hardness • Practical Task 2: • Use a file to compare the hardness of different materials such as copper, brass, aluminum and steel test pieces and place them in order of hardness, starting with the hardest material.

20. 8. Toughness • Toughness is the property of a material that it does not break under a sudden shock. • We need the property of toughness where there is impact, shock and the need to absorb energy. • Tough materials have strength, ductility and malleability. Tough material withstand impact shock

21. 3. Technological properties • These properties relate to the behavior of the material during processing. (Fig. 2.18). • Castability: Castable materials are those which melt and can be poured into moulds, e.g., cast iron, lead, tin ,copper alloys, gold.

22. 3. Technological properties • Re-formability: Re-formable materials are those materials that undergo a plastic change under the effect of force, and yet retain their integrity. • Examples of such processes are compressing, stretching, pressing, and bending.

23. 3. Technological properties • Machinability: Machinable materials are those materials that can be processed by parting, cutting or wearing off.

24. 3. Technological properties • Weldability: Weldable materials are those materials that can be joined locally by material bonding resulting from heat or pressure (fusion welding or pressure welding).

25. Activity 2: • Visit the engineering materials class’s blog created by your instructor and answer the following questions: http://iat-dxb-robotics-sh.blogspot.com/ • Why pieces of cast iron can not be bent? What are the properties that the material should have in order to be bent? • Give examples of situations where the material is subjected to tensile, compression and shear stress. • Classify the materials; lead, rubber, steel, and concrete under headings elastic, plastic, and brittle.