Properties of Materials

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Properties of Materials

• Engineering Materials
• Chapter 2

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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

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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

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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

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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

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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

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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!

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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

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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

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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

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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

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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

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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

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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

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Summary Critical Concepts

• Glance through glossary of terms
• Review bullet points on p. 67

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Case History

• Stiffness-driven designs
• Load v. efficient shape
• Example windshield wiper design
• Thin-walled round steel tubes v. aluminum