Properties of Materials

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2. Chapter 2: Goals. Identify important properties for material selectionsCompare properties among different material groupsUnderstand testing procedures

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Properties of Materials

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1. 1 Properties of Materials Engineering Materials Chapter 2

2. 2 Chapter 2: Goals Identify important properties for material selections Compare properties among different material groups Understand testing procedures & data Identify & thoroughly understand mechanical properties of: Stiffness Strength Toughness

3. 3 Chapter 2: Purpose Identify and discuss the properties often used in making key material selections Understand how these properties are measured Understand how to interpret data from the various test methods

4. 4 Chapter 2: Introduction Establish a vocabulary of properties Show how these properties apply to different material groups In some instances, the testing technique will be described in detail

5. 5 2.1 The Property Spectrum Choosing a material is similar to buying a car Primary categories of materials shown in Fig 2-1 Chemical measured in a laboratory Physical mainly non-destructive Mechanical response of an applied force Manufacturing Shape and surface features Look at terms under headings for each material Much cross-over in terms, i.e. thermal expansion

6. 6 2.1 The Property Spectrum International Standards Organization (ISO) certification Part of process is to document testing procedures Various Standards Organizations have developed standard test procedures ASTM, ISO, ANSI, CEN, DIN, BSI

7. 7 2.2 Chemical Properties Composition Metals - % of elements Polymers monomer with chain length Mixture & filler information Ceramics stoichiometric makeup Sometimes volume fraction of 2 or more compounds Binder information Phases present, crystal structure, grain size, porostiy, etc. Composites details of matrix and reinforcement Volume fractions Orientation of reinforcement Try to avoid using trade names!

8. 8 2.2 Chemical Properties Microstructure Metals grain size, phases present, heat treatment, inclusions How is grain size measured? (Fig 2-2, 2-3) Metallography & microtomy Crystal Structure & Stereospecificity X-ray diffraction SC, BCC, FCC, HCP Polymers semicrystalline Stereospecificity isotactic, syndiotactic, atactic Metals BCC v. FCC: Which tends to be brittle at low temperatures? Corrosion Resistance degradation of a material by reaction with the environment

9. 9 2.3 Physical Properties Thermal properties Thermal conductivity [Btu or W/(mK)] Basic equation for steady-state heat flow (Ficks 1st Law) Thermal expansion [in/(inF) or cm/(cmF)] Al v. Steel Takes place on the volume of material (Donut example) Polymers Maximum use temperature Heat distortion temperature Water absorption Electrical properties Resistivity, r (inverse of K) [mWcm or Wm] Conductivity = inverse of r Metals v. Polymers or ceramics

10. 10 2.3 Physical Properties Magnetic properties Permeability, retentivity, hysteresis loss, coercivity, intrinsic induction, etc. Ferromagnetism Fe, Ni, Co, Gd, Dy Measure of response to a magnetic field Flux density, B (B-H curve, Fig 2-6) Importance and application of hysteresis loop What materials? Gravimetric mass of materials Density & specific gravity (used with cost) Porosity theoretical v. apparent Optical properties

11. 11 2.4 Mechanical Properties (Fig 2-7) Stress (Fig 2-8,2-9) [N/m2 or Pa] Elastic v. plastic Elastic modulus, E Strain Hookes Law (Fig 2-10) Example p. 37 Materials Fig 2-11 Tensile test (Fig 2-12, 2-13, 2-14) Gage marks for strain measurement Extensometer Proportional limit, yield stress (0.2%), UTS Ductility - % elongation, % area reduction

12. 12 2.4 Mechanical Properties Two s-e curves: Engineering (Fig 2-15) True (Fig 2-16) Work or strain hardening Significance of exponent Poissons ratio (Fig 2-17) 0.2 0.35 Stress-strain testing Table 2-1, 2-2 Resilience elastic energy absorption Fig 2-18, 2-19

13. 13 2.4 Mechanical Properties Shear properties Fig 2-20 Shear modulus (Fig 2-21) Hardness tests (Fig 2-22 2-26) Mohs, Brinell, Rockwell, Knoop, Vickers Shore Durometer Impact tests (Fig 2-27) Impact strength [J/m3] NDT or DBTT (Fig 2-28) Long-term Serviceability Endurance limity, Creep, Stress rupture (Fig 2-29 2-31) Fracture mechanics Fracture Toughness, Kc Table 2-4

14. 14 2.5 Manufacturing Considerations Surface finish (Fig 2-32) Roughness, waviness (Fig 2-34) Profilometers (Fig 2-33) Cutoff width Surface texture (Fig 2-35 2-38) Size and shape Stock tolerances

15. 15 Summary & Critical Concepts Glance through glossary of terms Review bullet points on p. 67

16. 16 Case History Stiffness-driven designs Load v. efficient shape Example: windshield wiper design Thin-walled round steel tubes v. aluminum

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