Aircrafts Manufacturing Mechanical Properties of Materiai

Aircrafts Manufacturing
Mechanical Properties
of Material
Items to be covered
• Introduction on mechanical
properties
• Force
• Stress & types
• Strain
• Stress-strain curve
• Stress terms
 Proportional limit
 Elastic limit
 Yield stress
Ultimate strength
 Fracture strength
Strain terms
 Flexibility
 Ductility
• Energy terms
 Resilience
 Toughness
• Mechanical properties are important
in understanding and predicting
a material's behavior under load.
• Quantities of force, stress, strain,
strength, toughness, hardness,
friction and wear can help to
 Identify the properties of a material
(polymer, ceramic and metal).
 Understand reasons of failure.
Select and design of dental

restorations and appliances.
• Standardization of laboratory tests is

essential to control quality and
permit comparison of results
between investigators.
Force
• One body interacting with another

generates force. Forces may be applied
through actual contact of the bodies or
at a distance (e.g., gravity).
• The International System Unit of force

(SI unit) is the Newton (N).
Stress
 When a force acts on a body tending to produce
deformation, a resistance is developed to this external force
application.
 Definition: It is the Internal resistance to the externally

applied force.
 It is denoted by (σ)
 Stress (σ)= Force/Area (fig.1).
 Pascal = 1 N / m².
 Commonly stress is reported in terms of

megaPascals (MPA). MPA=106 Pascal.
Fig.1:Stress measurements
Types of stresses
1. Axial stresses
Compressive stress
Compression results when the body is subjected

to two sets of forces directed towards each
other in the same straight line. (fig.2)
Tensile stress
Tension results in a body when it is subjected
to two sets of forces directed away from each
other in the same straight line. (fig.2)
Fig.2.Types of axial stresses
• Axial
Compressive
Tensile
2. Non axial stresses
Shear stress
Shear is the result of two sets of forces

directed towards each other but not in the
same straight line.(fig.3)
Torsion
It results from the twisting of the body. (fig.3)
Bending
It results by applying bending movement.(fig.3)
Fig.3.Types of non axial stresses
• Non Axial
Shear
Torsion
Bending
Strain
• Definition: It is the change in length per unit
length.
• It represents the relative deformation of
an object that is subjected to stress.
• It may be elastic, plastic or both elastic and
plastic.
• It is denoted by “ε”
• Designated as ∆L / L. So, it is unitless.
• Strain(ε)= Deformation/Original length
• When the force is applied, the rod's
length changes from its original
length L0, to the extended length
L1. The resulted strain, ɛ, is given by
ɛ = (L1- L0)/ L0 (fig.4)

Fig.4:strain
In an object
subjected to
stress
Stress-Strain Relationship
• If a bar of material is subjected to an applied
force, F, the magnitude of the stress and the
resulting deformation (ɛ) can be measured.
• This is done with tensile, compressive or shear
loading of samples using universal testing
machine (Fig.5).
• Graph representing stress (or load) and strain
(elongation) can be obtained (Fig.6).
Fig.5: Universal testing
machine
Fig.6: Stress-strain curve for a material
subjected to tensile stress.
Stress-Strain Behavior (types of strain)
1. Elastic deformation
• Reversible: When the stress is removed, the
material returns to the dimension it had
before the loading.
2. Plastic deformation
• Irreversible: When the stress is removed, the
material does not return to its previous
dimension.
I. Stress terms
1.Proportional Limit
• It is the maximum stress up to which,
the stress is linearly proportional to
strain. (fig.6)Point A
• A material with high value of

proportional limit can withstand
greater stress without permanent
deformation.
• For example, a fixed partial denture that
is permanently deformed by excessive
occlusal forces would exhibit altered occlusal
contacts.
2. Elastic Limit
• Maximum stress a material can withstand
without undergoing permanent
deformation.
• It describes the elastic behavior of the

material. (fig.6)Point B
• The elastic and proportional limits
have nearly the same values, as they
represent the same phenomena.
3. Yield Stress or Proof stress

• It is the stress at which materials
start to show permanent
deformation.(fig.6) Point C
4. Ultimate(Tensile or compressive)
Strength or stress
• Maximum stress that the material
can withstand before failure
(fracture) under tension or
compression respectively.
• The material could not withstand

any more stresses, as it will fracture.
(fig.6) Point D
• The yield strength is often of greater
importance than ultimate strength
in design and material selection
because it is an estimation of when a
material will start to deform
permanently.
5. Fracture strength or stress
• It is the strength at which the
material fractures. (fig.6) Point F
II. Strain terms
1. Flexibility
• The maximum flexibility is defined as the
strain occurring when the material is
stressed to its proportional unit.
Significance
• A larger strain or deformation with
slight stresses is an important
consideration in orthodontic appliances.
• Impression materials should have
large flexibility or elastic
deformation to withdraw through
severe undercuts without permanent
deformation.
2. Ductility
• The amount of plastic strain
produced in the specimen before
fracture.
• Or the ability of a material to be
drawn and shaped into wire by
means of tension.
• When tensile forces are applied, the

wire is formed by permanent
deformation.
• However, malleability of a substance
represents its ability to be
hammered or rolled into thin sheets
without fracturing.
Significance
• High ductility and malleability are
useful in adapting metallic
restorations to the margins by
burnishing.
• Very thin pure direct filling gold foil
is available for restorations.
• Orthodontic wires are drawn from

cast ingot.
• The terms ductility and malleability are often used
interchangeably. They are similar in that they both refer to
a metal’s ability to withstand stress without rupturing, but
opposite in terms of the type of stress being applied.
Ductility has to do with tensile stress, whereas malleability
deals with compressive stress.
Brittleness :
 If a material showed no or very little
plastic deformation on application of load
it is described as being brittle.
 A brittle material
fractures at or near
its proportional limit.

Ductile material Brittle material
1) Is the ability of a 1) brittle material

Material to withstand fractures at or near
Plastic deformation its proportional limit.
Under tensile stress
Without fracture.
Fracture occur far Fracture occur at or

Away from P.L near P.L

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Aircrafts Manufacturing

Select and design of dental

• Standardization of laboratory tests is

• One body interacting with another

• The International System Unit of force

 Definition: It is the Internal resistance to the externally

 Stress (σ)= Force/Area (fig.1).

 Commonly stress is reported in terms of

Compression results when the body is subjected

Shear is the result of two sets of forces

length changes from its original

length L0, to the extended length

L1. The resulted strain, ɛ, is given by

ɛ = (L1- L0)/ L0 (fig.4)

• A material with high value of

• It describes the elastic behavior of the

3. Yield Stress or Proof stress

• The material could not withstand

• When tensile forces are applied, the

• Orthodontic wires are drawn from

its proportional limit.

1) Is the ability of a 1) brittle material

Fracture occur far Fracture occur at or

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