Topic 3 - Material Science

TOPIC 3: MATERIAL

PROPERTIES & BEHAVIOR

PREPARED BY :

NORSHEILA BINTI BUYAMIN

PENSYARAH POLITEKNIK UNGKU OMAR

DJJ3213 MATERIAL SCIENCE

MATERIAL PROPERTIES

(A) Physical Properties

is a characteristic that can be observed or measured without changingThe composition of the substance

Physical properties describe the substance itself Examples:

i. Changes of states

ii.Colour

iii.Mass, shape, length

iv.Magnetic properties

(B) Thermal Properties

(C) Mechanical Properties

Thermal Conductivity A property of the material (the materials ability to transfer heat)

Thermal diffusivity The ratio of thermal conductivity to the volumetric heat capacity

of material (the ration of the materials ability to transfer heat to

its capacity to store that)

Specific heat Melting point Thermal expansion

Mechanical properties determine a materials behavior when subjected to mechanical stresses

Properties include elastic modulus, ductility, hardness, toughness, brittleness and various measures of strength.

(D) Electrical Properties

It is well known that one of the subatomic particles of an atom is the Electron.

The electrons carry a negative charge and under certain conditions canMove from atom to atom

Examples of electrical of properties:i.Electrical conductivity measure of how well a material accommodates

the movement of an electric charge

ii. Electrical resistivity the opposition of a body or substance to the

flow of electrical current through it

iii. Temperature Coefficient of Resistivity

MECHANICAL PROPERTIES

Strength (Kekuatan)

Is the ability of a material to withstand an applied stress without

failure or deformation.

Tensile & Compressive Strength (kN), Shear & Bending Strength, Proof Stress, etc.

^High strength double girder overhead crane having lifting capacity

up to 500ton.

Hardness (Kekerasan) Ability of resistance to localized plastic deformation or

penetration (e.g., a small dent, wear or a scratch).

Anti scratch sapphire glass

Turning a metal rod it in a lathe by tool

bit (harder than workpiece).

Elasticity (Keanjalan)

Elastic deformation is nonpermanent, which means that

when the applied load is released, the piece returns to its

original shape.

Modulus of elasticity (Youngs modulus, E [GN/m2])

^ Elastic bow pushes the arrow

forward.

v Fishing rods or poles

^ Elastic chest expander

^ Rat trap

> Car suspension

springs

Plasticity (Keplastikan)

Is a permanent deformation; the object does not return to

its original shape when the stress is removed.

Plaster have highly plastic

deformations and ductile fracture.

1981 50 sen Malaysia double striking Error coin

The stamping images on coins and ornamental work

show plasticity of metal.

Permanent plastic deformation after

tube bending

Ductility (Kemuluran)

Ability to deform plastically (elongation or bending) before

fracture under tensile force.

This property important in drawing and pressing process.

Bending a ductiles mild steel

Tensile test of an

AlMgSi alloy. The

local necking & the

cup and cone

fracture surfaces

are typical for

ductile metals.

Tensile test of a

nodular cast iron

with very low

ductility.

Aluminium Wire are made by

drawing out through a die hole.

Handmade aluminium wire

bicycle, art scale model.

Toughness (Keliatan)

Ability of a material to prevent impact load without

fracture.

Automobiles Bumpers are designed

to allow car to sustain an impact

without damage to the vehicle's

safety systems

Motocycle helmet able to reduce impact force to

prevent injury to the occupant.

High toughness torque wrench is

used to torque the bolts/nuts during

installing wheels.

Brittleness (Kerapuhan)

The ability of the materials to break/fracture without a

permanent deformed when a tension force is applied.

Brittle fracture of metal

Brittle fracture of glass

brittle fracture and stress-

corrosion cracking of

steel pipe.

Brittle fracture of a hollow stone sculpture.

MATERIAL BEHAVIOURS

(A) Creep When a metal or an alloy is under a constant load or stress, it may

undergo progressive

plastic deformation over a period of time. This time dependent strain

called creep.

For example, an engineer selecting an alloy for the turbine blades of a gas turbine engine must choose an alloy with a very low creep rate

so that the blades can remain for in service for a long period of time

before having of replaced.

A typical creep curve for a metal. The curve represents the time versus strain

behavior of a metal or alloy under a constant load at constant temperature.

(B) Fatigue

In many types of service applications metal parts subjected to repetitive or cyclic stresses will fail due to fatigue loading at a much

lower stress than that which the part can withstand under the

application of a single static stress.

These failures that occur under repeated or cyclic stressing are called fatigue failure.

Example: machine parts in which fatigue failures are moving parts such as shafts, connecting rods and gears.

Schematic diagram of an R.R. Moore reversed-bending fatigue machine

Stress versus number of cycles (SN) curve for fatigue failure

(C) Fracture

One of the important and practical aspects of materials selection in the design, development and production of the new components is

the possibility of failure of the component under normal operation.

Failure can defined as the inability of the material or a component to: Perform the intended function Meet performance criteria although it may still be operational Perform safely and reliably even after deterioration

Yielding, wear, buckling (elastic instability), corrosion and fracture are examples of situations in which a component has failed.

Fracture is separation of a solid under stress into two or more parts. In general metal fractures can be classified as ductile or brittle, but a

fracture can be a mixture of the two.

i. Ductile Fracture

Occur after extensive plastic deformation and is characterized by slow crack propagation

i. Brittle Fracture

Proceed along characterized by crystallographic planes called cleavage planes and has rapid crack propagation