MAB2023/Jan’09/om

1 MAB2023 Course Outcomes MAB2023 Course Outcomes

Set up related material engineering laboratory experiments as well as interpreting results for further discussion and conclusion.

Apply relevant engineering materials knowledge to the respective industry.

Propose the immediate possible solution to resolve the identified problem related to material engineering application in industry.

Identify the root cause of the failure problems in engineering materials components.

Describe the properties and degradation factors involved in engineering materials design and selection1

2

3

4

5

At the end of the course, the students should be able to:At the end of the course, the students should be able to:

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2

Metals and Alloys

Ceramics and GlassesPolymers

Composites

Wire-

reinforced cement (Cermet)

Filled polymers

CFRP GFRP

Steel-cord tyres

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3 Mechanical Properties of Materials

Learning Outcomes: students should be able to address the following issues...

1.

Familiarization with the properties that must be reviewed when making materials selection.

2.

Acquiring the knowledge of how properties apply to different material systems.

3.

An understanding of pitfalls (drawback/consequence) to avoid in performing property tests and in using property data.

4.

Thorough understanding of the differences among the properties of stiffness, ductility, strength and toughness.

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4 Tensile TestTensile Test

The key mechanical properties obtained from a Tensile Test:1-Modulus of Elasticity, E; 2-Yield Strength, Y.S.3-Tensile Strength; 4-Ductility, 100xєfailure (elastic recovery occurs after fracture); 5-Toughness (measured under load; hence the dashed line is vertical)

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5 The tensile test is the most common test for determining such mechanical properties of materials as strength, ductility, toughness, elastic modulus, and strain-hardening capability.

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6

When the load is first applied, the specimen elongates in proportion to the load; this behavior is called linear elastic.

The engineering stress (nominal stress) is defined as the ratio of the applied load, P, to the original cross-

sectional area, A0

of the specimen:

Tensile TestTensile Test

[1.1] Stress, gEngineerinoA

P

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7 Tensile Test

The engineering strain is defined as

where l is the instantaneous length of the specimen.

As the load is increased, the specimen begins (at some level of stress) to undergo

permanent (plastic) deformation.

The stress at which this phenomenon occurs is known as the yield stress, Y, of the material.

Mechanical properties for various metallic and nonmetallic materials are given in Table 2.2.

[1.2] )( Strain, gEngineerino

o

llle

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Y usually is defined as the point on the stress–strain curve that is offset

by a

strain of 0.002, or 0.2% elongation.

As the specimen (under a continuously increasing load) begins to elongate, its cross-sectional area decreases permanently

and uniformly

throughout its gage length.

Figure shows a schematic illustration of the loading and the unloading of a tensile-test specimen. Note that, during unloading, the curve follows a path parallel to the original elastic slope.

Tensile Test

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The maximum engineering stress is called the tensile strength or ultimate tensile strength (UTS) of the material.

If the specimen is loaded beyond its ultimate tensile strength, it begins to neck

or neck down.

As the test progresses, the engineering stress drops further and the specimen finally fractures at the necked region.

The engineering stress at fracture is known as the breaking

or fracture stress.

Tensile Test

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The ratio of stress to strain in the elastic region is the modulus of elasticity, E, or Young’s modulus:

This linear relationship is known as Hooke’s law.

The modulus of elasticity is essentially a measure of the slope of the elastic portion of the curve and, hence, the stiffness of the material.

The absolute value of the ratio of the lateral strain to

the longitudinal strain is known as Poisson’s ratio and

is denoted by the symbol V .

Tensile Test

[1.3] ,elasticity of Moduluse

E

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11 Elastic Deformation: Stress-Strain Behavior

Elastic Properties: (isotropic materials)

Poisson’s ratio ()

z

y

z

x

12GEG = shear modulus

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12 Elastic Deformation: Stress-Strain Behavior

Anelasticity:

time dependent elastic behavior. Elastic strain recovery with time.

for metals is small, but significant for some polymeric materials

viscoelastic behavior.

G G = shear modulus

For shear:

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13 Mechanical properties for various metallic and nonmetallic materials

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14 Ductility

Ductility is the extent of plastic deformation that

the material undergoes before fracture.

There are two common measures of ductility. The first is the total elongation of the specimen:

where l and Io

are measured.

[1.4] x100)(

Elongationo

of

lll

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15 Ductility

The second measure of ductility is the reduction of area:

where and are the original and final (fracture) cross-sectional areas, respectively, of the test specimen.

fA0A

[1.5] )(

area ofReduction o

fo

AAA

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16 Ductility

Figure shows the approximate relationship between elongation and tensile reduction of area for various groups of metals.

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17

A cylindrical specimen of steel having an original diameter of 12.8 mm is tensile tested to fracture and found to have an engineering fracture strength of 460 MPa. If its cross sectional diameter at fracture is 10.7 mm, determine:a)The ductility in terms of % reduction areab)The true stress at fracture.

DUCTILITY Case StudyDUCTILITY Case Study

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18 Impact Test Impact Test (Energy Absorbed in Fracture)(Energy Absorbed in Fracture)

A typical impact test consists of placing a notched specimen in an impact tester and breaking it with a swinging pendulum.

In the Charpy

test, the specimen is supported at both ends (a); in

the Izod

test, it is supported at one end like a cantilever beam (b).

From the amount of swing of the pendulum, the energy dissipated in breaking the specimen can be obtained; this energy is the impact toughness of the material.

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QM(Tensile): A force of 100,000 N is applied to a 10 mm x 20 mm iron bar having a yield strength of 400 MPa and a tensile strength of 480 MPa. Determine (a) whether the bar will plastically deform and (b) whether the bar will experience necking.

Tensile Case StudyTensile Case Study

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QM(Design): A tensile testing apparatus is to be constructed that must withstand a maximum load of 220,000 N. The design calls for two cylindrical support posts, each of which is to support half of the maximum load. Furthermore, plain carbon steel (1045) steel ground and polished shafting rounds are to be used; the maximum yield and tensile strength of this alloy are 310 MPa and 565 MPa, respectively. Specify a suitable diameter for these support posts.

Mechanical Properties Of Metals: Case 2Mechanical Properties Of Metals: Case 2

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a) A polymer bar’s dimensions are 1 in. x 2 in. x 15 in. The polymer has a modulus of elasticity of 600,000 psi. What force is required to stretch the bar elastically to 15.25 inches?

b) A common copolymer is produced by including both ethylene (C2

H4

) and propylene (C3

H6

) monomers in the same chain. Given a degree of polymerization of 5000, determine the molecular weight of the polymer produced using 1 kg of ethylene and 3 kg of propylene.

MECHANICAL PROPERTIES OF POLYMERS: ProblemsMECHANICAL PROPERTIES OF POLYMERS: Problems

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22 Hardness TestHardness Test

Hardness usually is defined as resistance to permanent indentation.

Several test methods have been developed to measure the hardness of materials, using different indenter materials and shapes.

Figure/table shows a general characteristics of hardness-testing methods and formulas for calculating hardness.

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23 Hardness TestHardness Test

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24 Brinell Hardness Test

The Brinell

hardness number (HB) is defined as the ratio of the load P to the curved surface area of the indentation.

Figure shows the indentation geometry in Brinell

hardness testing: –(a) annealed metal; –(b) work-hardened metal; –(c) deformation of mild steel under a spherical indenter.

•Note that the depth of the permanently deformed zone is about one order of magnitude larger than the depth of indentation. •For a hardness test to be valid, this zone should be developed fully in the material.

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25 Rockwell Hardness Test

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Magnitude of loads dictate the type of test.

As values rise above 100 or drop below 20 on any scale, better to switch scales.

Sample thickness = 10X penetration depth.

Indentations should be separated by at least 3 indentation diameters.

Indentations should me made on smooth flat surfaces.

Rockwell Hardness Test

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Rockwell Hardness Test--

Superficial:

Rockwell Hardness Test

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28 Other Hardness TestsOther Hardness Tests

Vickers test

This test, formerly known as the diamond pyramid hardness test, uses a pyramid-shaped diamond indenter and a load that ranges from 1 kg to 120 kg. Indicated by HV.

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29 Hardness

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30 Hardness and StrengthHardness and Strength

A relationship has been established between the ultimate tensile strength (UTS) and the Brinell

hardness (HB) for steels as measured for a load of 3000 kg.

The following is in SI and English units respectively,

3.5( ) (2.13)500( ) (2.14)

UTS HBUTS HB

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31 Bending Strength of CeramicsBending Strength of Ceramics

A commonly used test method for brittle materials is the bend or flexure test.

Two bend-test methods for brittle materials: (a) three-

point bending; (b) four-point bending.

The areas on the beams represent the bending-moment diagrams, described in texts on mechanics of solids.

–

Note the region of constant maximum bending moment in (b); by contrast, the maximum bending moment occurs only at the center of the specimen in (a).

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Note the region of constant maximum bending moment in (b); by contrast, the maximum bending moment occurs only at the

center of the specimen in (a).

Bending Strength of CeramicsBending Strength of Ceramics

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QCe2: A fully stabilized, cubic polycrystalline zirconia advanced ceramic, ZrO2

sample has a fracture toughness of KIC = 3.8 MPa when tested on a four-

point bend testing apparatus. If the sample fails at a stress of 450 MPa, what is the size of the largest surface flaw? Assume the shape factor constant,Y =

m

Bending Strength of Ceramics: ProblemBending Strength of Ceramics: Problem

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QCe1: A three-point bend test is performed on a block of silicon carbide that is 10 cm long, 1.5 cm wide, and 0.6 cm thick and is resting on two supports 7.5 cm apart. The sample breaks when a deflection of 0.09 mm is recorded. Calculate (a) the force that caused the fracture and (b) the flexural strength. The flexural modulus for silicon carbide is 480 GPa. Assume that no plastic deformation occurs.

Mechanical Properties Of Ceramics: Problems