Engineering Practicum Baltimore Polytechnic Institute M. Scott

(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?

Materials Science and Engineering

Engineering Practicum Baltimore Polytechnic Institute M. Scott

Materials Science and Engineering

Lesson Outline1. History2. Structure3. Properties4. Testing Methods5. Materials Testing Laboratory

Questions to answer…Why do things break?Why are some materials stronger than others?Why is steel tough, glass brittle?What is toughness, strength, brittleness?How do we quantify material properties?

Engineering Practicum Baltimore Polytechnic Institute M. Scott

Solids1. 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

1. Form2. Held together by Chemical and Physical bonds3. Atoms in equilibrium with interatomic forces at fixed

distances from other atomsCloser 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

Solids

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

• PlasticLarger 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) Brittleb) Ductilec) Completely Ductile

Examples:d) Cast Irone) Aluminumf) Putty*

Engineering Practicum Baltimore Polytechnic Institute M. Scott

Stress-Strain Curves

Stre

ss, s

(MPa

)

Strain, e (m/m)

Ds

De

E

1

1. Proportionality Limit2. Elastic Limit3. Yield Strength4. Ultimate Tensl Strgth5. Fracture StrengthE = Young’s Modulus,

Modulus of ElasticityElastic Region

Plastic Region

2

3

Tensile Test

45

E

0.2%

Engineering Practicum Baltimore Polytechnic Institute M. Scott

Stress-Strain Curves

Engineering Practicum Baltimore Polytechnic Institute M. Scott

Stress-Strain Curves• Which curve is typical of:– A ductile material– A brittle material

Young’s Modulus is the resistance of a material to deformation

Engineering Practicum Baltimore Polytechnic Institute M. Scott

Stress-Strain Curves

Engineering Practicum Baltimore Polytechnic Institute M. Scott

Stress-Strain Curves

Engineering Practicum Baltimore Polytechnic Institute M. Scott

Young’s Modulus

Engineering Practicum Baltimore Polytechnic Institute M. Scott

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?

Material Properties

Engineering Practicum Baltimore Polytechnic Institute M. Scott

What is a Material Property?

1. A quantitative trait – tells us something about a material, numerically

2. They have units3. Unaffected by material form4. May be:

1. Constant 2. A function of independent variables (like

temperature)

Material Properties

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

Engineering Practicum Baltimore Polytechnic Institute M. Scott

Mechanical Material Properties

• Terminology

Engineering Practicum Baltimore Polytechnic Institute M. Scott

Mechanical Material Properties Testing

• Tensile Test

specimenextensometer

Engineering Practicum Baltimore Polytechnic Institute M. Scott

Mechanical Material Properties Testing

• Bending Test – Setup

Engineering Practicum 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

• Brief review of lab instructions• Tension specimen preparation tomorrow in rm 164

– EpoxyA polymer formed by the chemical reaction of a “resin” and a “hardener” – two viscous liquids

Problems with Epoxy:1. Irreversible curing2. Very messy3. Must mix two equal portions4. Possible endocrine disrupter and main cause of occupational

asthma

Material Laboratory Preparation