NAZARIN B. NORDIN [email protected] What you will learn: Strength, elasticity, ductility, malleability, brittleness, toughness, hardness Ferrous/ non-ferrous
What you will learn: Strength, elasticity, 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
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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
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Definition: the strength of a material is its ability to
withstand an applied stress without failure 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. Strength of
materials
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Elasticity Definition: the tendency of a body to return to its
original shape after it has been stretched or compressed.
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Other terms used in describing materials Hardness
Toughness
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Hardness A hard material is one that resists indentation or
abrasion by another material.
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Toughness A material is said to be tough when a large amount of
energy is required to fracture it.
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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.
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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.
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Malleability Metals that can be hammered and bent without
cracking are said to be malleable. Lead is an example of a
malleable material.
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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.
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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 bolts
dimensions is known as strain. Stress is calculated by dividing the
applied force by the cross-sectional area of the bolt. Stress =
Perpendicular Force/Cross-sectional area
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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.
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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.
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Example 2: A connecting rod has a cross- sectional area of
200mm 2 and it carries a compressive force of 2.4 tonnes (in N).
Calculate the compressive stress in the connecting rod.
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Example 3: The hand brake linkage shown in Figure carries a
tensile force of 600 N. Calculate the shear stress in the clevis
pin, which is 12mm in diameter.
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In this case the shearing action is attempting to shear the
clevis pin across two cross-sectional areas.
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Example 4: A propeller shaft coupling of a truck is secured by
four bolts of 14 mm diameter 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 500
N.m.
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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
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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 = 0.0006
Note: strain does not have any units.