1. 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

2. Engineering Practicum Baltimore Polytechnic Institute M. Scott Materials Science and Engineering Lesson Outline 1.History 2.Structure 3.Properties 4.Testing Methods 5.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?

3. 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

4. Engineering Practicum Baltimore Polytechnic Institute M. Scott 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,  – load / unit area. Units: p.s.i. or Mpa Strain,  – defrmtn / unit length. Units: dimensionless Solids

5. 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”

6. 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*

7. Engineering Practicum Baltimore Polytechnic Institute M. Scott Stress-Strain Curves Stress,  (MPa) Strain,  (m/m)     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 2 3 Tensile Test 4 5  0.2%

8. Engineering Practicum Baltimore Polytechnic Institute M. Scott Stress-Strain Curves

9. 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

10. Engineering Practicum Baltimore Polytechnic Institute M. Scott Stress-Strain Curves

11. Engineering Practicum Baltimore Polytechnic Institute M. Scott Stress-Strain Curves

12. Engineering Practicum Baltimore Polytechnic Institute M. Scott Young’s Modulus

13. 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

14. 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 units 3.Unaffected by material form 4.May be: 1.Constant 2.A function of independent variables (like temperature) Material Properties

15. 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

16. Engineering Practicum Baltimore Polytechnic Institute M. Scott Material Properties

17. Engineering Practicum Baltimore Polytechnic Institute M. Scott Mechanical Material Properties Terminology

18. Engineering Practicum Baltimore Polytechnic Institute M. Scott Mechanical Material Properties Testing Tensile Test specimen extensometer

19. Engineering Practicum Baltimore Polytechnic Institute M. Scott Mechanical Material Properties Testing Bending Test – Setup

20. Engineering Practicum Baltimore Polytechnic Institute M. Scott Mechanical Material Properties Testing Bending Test – Stress and Strain

21. 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 Modes of Buckling

22. Engineering Practicum Baltimore Polytechnic Institute M. Scott 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 Material Laboratory Preparation