1. BTE 1013 ENGINEERING SCIENCEs
7. materials
NAZARIN B. NORDIN

2. What you will learn:
Strength, elesticity, ductility, malleability, brittleness, toughness, hardness
Ferrous/ non-ferrous metals, tensile stress, yield stress, shear force, percentage of elongation and percentage of reduction in plain carbon steel, shear force, bending moment and fatigue test

3. 7.1 Strength, elasticity, ductility, malleability, brittleness, toughness, hardness
7.2 Ferrous/non-ferrous metals, tensile stress, yield stress, shear force, percentage of elongation, percentage of reduction in plain carbon steel, shear force, bending moment and fatigue test

4. Strength of materials
For practical purposes, components are designed to withstand forces and loads that a device is designed for and, so long as the instructions for use and maintenance, such as safe loads and tightening torques, are observed, problems should not be experienced.

5. Other terms used in describing materials
Hardness
Toughness

6. Hardness
A hard material is one that resists indentation or abrasion by another material.
The Brinell test is one method that is used to measure hardness and it operates by pressing
A hardened metal carbide ball under a standard load into the surface of the specimen. The dimensions of the impression made are used to calculate the Brinell Hardness Number (BHN).

7. Toughness
A material is said to be tough when a large amount of energy is required to fracture it.

8. Brittleness
Materials that break without undergoing local distortion and are unable to withstand sharp blows are said to be brittle. Most types of cast iron are brittle.

9. Ductility
A material that can be drawn out by tensile force is said to be ductile. The steel sheet that is used in the construction of motor car panels is of a type known as deep drawing steel and this is a ductile material.

10. Malleability
Metals that can hammered and bent without cracking are said to be malleable. Lead is an example of a malleable material.

11. Non-ferrous metals
These are mainly alloys that contain no iron. Commonly used non-ferrous alloys are those made from copper, lead, tin, aluminium or magnesium. Non-ferrous alloys are used extensively in automotive engineering.

12. Stress
Forces that tend to stretch, or pull something apart, are known as tensile forces and they produce two important effects:
1. In trying to pull the bolt apart, internal resisting
forces are created and these internal forces are
known as stress.
2. The length of the bolt will increase, and this change in the bolt’s dimensions is known as strain.
Stress is calculated by dividing the applied force
by the cross-sectional area of the bolt.
Stress = Force/Cross-sectional area

13. Types of stress There are three basic forms of stress:
1. tensile stress;
2. compressive stress;
3. shear stress – torsional stress is a form of shear stress.

16. Examples of stress measure
Example 1: A cylinder head bolt with an effective diameter of 15mm carries a tensile load of 10 kN. Calculate the tensile stress in the bolt.
Stress is normally quoted in kN/m2, or MN/m2.
Stress may also be stated in Pa (pascals);
1Pa = 1N/m2.

17. Example 2: A connecting rod has a cross-sectional area of 200mm2 and it carries a compressive force of 2.4 tonnes. Calculate the compressive stress in the
connecting rod.

18. Example 3: The hand brake linkage shown in Figure below carries a tensile force of 600 N. Calculate the shear stress in the clevis pin, which is 12 mm in diameter.

19. In this case the shearing action is attempting to shear the clevis pin across two cross-sectional areas.

20. Example 4: A propeller shaft coupling of a truck is secured by four bolts of 14mmdiameter that are equally spaced at a radius of 50mm from the centre of the propeller shaft. Calculate the shear stress in each bolt when the shaft is transmitting a torque of 500N m.

22. Strain
When a load is applied to a metal test bar a change of shape takes place. A tensile load will stretch the bar and a compressive load will shorten it. This change of shape is called strain. The three basic types of strain are shown in Figure

24. Example strain measure
A steel rod 200mm in length stretches by 0.12mm when it is subjected to a tensile load of 2 tonnes. Determine the strain.
Solution
Strain = change in length/original length
= 0.12mm/200mm
Tensile strain in the steel rod =
Note: strain does not have any units.

26. THANK YOU