Materials Science and Engineering
(Pass in Remote Measurement Lab Report)
1. What is the relationship between
a) Tensile Strength and Length
b) Tensile Strength and Cross-sectional Area
c) Compressive Strength and Length
d) Compressive Strength and Cross-sectional Area
2. How could we determine the specific relationships?
Engineering Practicum
Baltimore Polytechnic Institute
M. Scott
Materials
Science and Engineering
Questions
answer…
Lesson to
Outline
Why
things break?
1. do
History
Why
some materials stronger than others?
2. are
Structure
Why
steel tough, glass brittle?
3. is
Properties
What
is toughness,
strength, brittleness?
4. Testing
Methods
How
we quantify
material
properties?
5. do
Materials
Testing
Laboratory
Engineering Practicum
Baltimore Polytechnic Institute
M. Scott
Solids
1. Form
–
–
–
–
Crystals
Glasses and Ceramics
Polymers
Elastomers
2. Held together by Chemical and Physical bonds
– Bonds holding atoms together
• Covalent
• Ionic
• Metallic
– Bonds holding molecules together
• Hydrogen bonds
• Van der Waals forces
Engineering Practicum
Baltimore Polytechnic Institute
M. Scott
Solids
1. Form
2. Held together by Chemical and Physical bonds
3. Atoms in equilibrium with interatomic forces at fixed
distances from other atoms
Closer or farther produces different restoring forces
4. Pushes on solids cause deformation (strain) which
generates reactive force (stress)
Stress, s – load / unit area.
• Units: p.s.i. or Mpa
Strain, e – defrmtn / unit length.
• Units: dimensionless
Engineering Practicum
Baltimore Polytechnic Institute
M. Scott
Solid Behavior
• Elastic
Loading and unloading returns material to its original
length, and can be done repeatedly – e.g. watch spring
• Plastic
Larger deformations are not reversible when “elastic
limit” is exceeded. Some materials are purely plastic –
e.g. putty
Hooke’s Law: “As the extension, so the force”
Engineering Practicum
Baltimore Polytechnic Institute
M. Scott
Solid Behavior
After tensile testing:
a) Brittle
b) Ductile
c) Completely Ductile
Examples:
a) Cast Iron
b) Aluminum
c) Putty*
Engineering Practicum
Baltimore Polytechnic Institute
M. Scott
Stress-Strain Curves
4
5
3
Tensile Test
1. Proportionality Limit
2. Elastic Limit
3. Yield Strength
4. Ultimate Tensl Strgth
5. Fracture Strength
E = Young’s Modulus,
Modulus of Elasticity
Elastic Region
Plastic Region
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Stress, s (MPa)
2
1
Ds
E
E
De
0.2%
Strain, e (m/m)
Baltimore Polytechnic Institute
M. Scott
Stress-Strain Curves
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Baltimore Polytechnic Institute
M. Scott
Stress-Strain Curves
• Which curve is typical of:
– A ductile material
– A brittle material
Baltimore Polytechnic Institute
Engineering Practicum
M. Scott
Young’s
Modulus is the resistance
of a material to deformation
Stress-Strain Curves
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Baltimore Polytechnic Institute
M. Scott
Stress-Strain Curves
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Baltimore Polytechnic Institute
M. Scott
Young’s Modulus
Engineering Practicum
Baltimore Polytechnic Institute
M. Scott
Material Properties
Questions we’ll answer:
1. What properties do we use to characterize materials?
2. How are those properties determined?
3. What are the parameters that affect materials in tension
and compression?
4. What are the optimal sizes of tension and compression
members to satisfy design requirements?
Engineering Practicum
Baltimore Polytechnic Institute
M. Scott
Material Properties
What is a Material Property?
1. A quantitative trait – tells us something about a
material, numerically
2. They have units
3. Unaffected by material form
4. May be:
1. Constant
2. A function of independent variables (like
temperature)
Engineering Practicum
Baltimore Polytechnic Institute
M. Scott
Material Properties
•
•
•
•
•
Physical – dimensions, density, porosity
Mechanical – strength, stiffness, hardness
Chemical – corrosion resistance, acidity or alkalinity
Thermal – conductivity, specific heat, expansion
Electric and Magnetic – conductivity, magnetic
permeability, dielectric strength
• Acoustical – sound transmission, sound reflection
• Optical – color, light transmission, light reflection
Engineering Practicum
Baltimore Polytechnic Institute
M. Scott
Material Properties
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Baltimore Polytechnic Institute
M. Scott
Mechanical Material Properties
• Terminology
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Baltimore Polytechnic Institute
M. Scott
Mechanical Material Properties
Testing
• Tensile Test
extensometer
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specimen
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M. Scott
Mechanical Material Properties
Testing
• Bending Test – Setup
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Baltimore Polytechnic Institute
M. Scott
Mechanical Material Properties
Testing
• Bending Test – Stress and Strain
Engineering Practicum
Baltimore Polytechnic Institute
M. Scott
Mechanical Material Properties
Testing
Compression Test
• Failure by buckling or crushing (or shattering glass)
Wood: Crush if L/d < 10, Buckle if L/d > 10
Modes of Buckling
Engineering Practicum
Baltimore Polytechnic Institute
M. Scott
Material Laboratory Preparation
• Brief review of lab instructions
• Tension specimen preparation tomorrow in rm 164
– Epoxy
A polymer formed by the chemical reaction of a “resin” and a
“hardener” – two viscous liquids
Problems with Epoxy:
1. Irreversible curing
2. Very messy
3. Must mix two equal portions
4. Possible endocrine disrupter and main cause of occupational asthma
Engineering Practicum
Baltimore Polytechnic Institute
M. Scott