Material properties

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Material properties, composition Failure and
degradation
Dr. Mohanad Talal Alfach
City, University of London
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Learning Objectives
After this lesson, students should be able to

• Classifying the materials in different classes
  (natural materials, metals, polymers, ceramics
  and glasses, and composites) according to their
  essential properties.
• Understanding the factors that affect the
  properties of materials.
• Define the essential materials properties.
• Explain a typical engineering stress-strain
  diagram of material and its important features.
• Determine elastic modulus, yield strength, and
  tensile strength from an engineering
  stress-strain diagram
• Understanding the materials failure and
  degradation mechanisms.
• Materials selection criteria for use in civil
  engineering design

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Engineering Connection
-When designing structures, engineers carefully
choose the materials by anticipating the forces
the materials (the structural components) are
expected to experience during their lifetimes.
-The mechanical properties of these materials
are the most important properties because all
service conditions and most end-use applications
in involve some degree of mechanical loading.
-Usually, ductile materials such as steel and
other metals are used for components that
experience tensile loads. -Brittle materials
such as concrete are used for components that
experience compressive loads.
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Factors that determine the properties of
materials
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So how does that affect the properties of the
materials?
Metals
Ceramics
Polymers
Metallic bonds
Ionic or Covalent bonds
Covalent bonds
High density
High stiffness
Low density
Hard/brittle
Ductile
Wide variety of other properties
Insulators
Good conductors of electricity and heat
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Definitions
Stress The force applied to produce deformation
in a unit area of a test specimen. Stress is a
ratio of applied load to the original
cross-sectional area
A
F
F
Elongation The increase in the length of a
specimen produced by a tensile load.
Strain The ratio of elongation to the original
length of the test specimen, or simply stated,
change in length per unit of the original length.
Lo
e
L
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Elastic Modulus (Youngs modulus) the slope of
the tangent to the stress-strain curve.
Yield point The first point of stress-strain
curve at which an increase the strain occurs
without the increase in stress.
Compression Test
The most common test performed on hardened
concrete. This test is performed on cylindrical
specimens standardized by ASTM C39. The standard
specimen size is 6 in. in diameter and 12 in.
high. (the compressive strength of normal-weight
concrete is between 21 MPa to 34 MPa)
Compression stress, s
FC
?? ?? ?? 4 ?? ?? ?? 2
Area, A
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Tensile Test
A tensile test is a scientific test process
involving the application of tension to a
specimen until it fractures. It is an important
type of test for determining a materials tensile
strength, yield strength and ductility.
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Stress-Strain Diagram

ultimate tensile strength
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necking
Strain Hardening
SlopeE
Fracture
yield strength
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Elastic region slopeYoungs(elastic) modulus
yield strength Plastic region ultimate tensile
strength strain hardening fracture
Plastic Region
Stress (F/A)
Elastic Region
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Strain ( ) (e/Lo)
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Tensile Strength Comparison
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Youngs Modulus Comparison
Graphite Ceramics Semicond
Metals Alloys
Composites /fibers
Polymers
E(GPa)

109 Pa
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Questions?