PROPERTIES OF MATERIALS

Goals and Purpose

Identify important properties for material selections

Compare properties among different material groups

Identify and discuss the properties often used in making key material selections

The Property Spectrum

Choosing a material is similar to buying a car

Primary categories of materials

Chemical – measured in a laboratory

Physical – mainly non-destructive

Mechanical – response of an applied force

Manufacturing – Shape and surface features

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

Properties of Materials

Chemical – relate to structure of material, its formation from the elements out of which it is made, and its reactivity with chemicals, other materials, and environments.  These properties are usually measured in a chemical laboratory

Physical – response of a material due to interaction with various forms of energy (i.e. magnetic, thermal, etc) and with the human senses.  Can usually be measured without destroying the material.

Mechanical – response of a material due to an applied force. Main focus for Machine Design.

Important Chemical Properties:

Composition

Microstructure

Phases

Corrosion resistance

Environmental resistance

Flammability

Grain size (related to strength and fatigue)

Passivity (related to corrosion)

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

Microstructure

Metals – grain size, phases present, heat treatment, inclusions. How is grain size measured?

Metallography , Crystal Structure, X-ray diffraction – SC, BCC, FCC, HCP

Metals – BCC v. FCC: Which tends to be brittle at low temperatures?

Corrosion Resistance – degradation of a material by reaction with the environment

Important Physical Properties:

Density

Color

Electrical conductivity

Glass transition temperature

Thermal conductivity

Thermal expansion

Permeability

Optical

Acoustical

Water absorption

Ferromagnetism

Thermal properties

Thermal conductivity [Btu or W/(m·K)]

Basic equation for steady-state heat flow
(Fick’s 1^st Law)

Thermal expansion

Al v. Steel

Polymers

Maximum use temperature

Heat distortion temperature

Water absorption

Electrical properties

Resistivity, r (inverse of K) [mW·cm or W·m]

Conductivity = inverse of r

Metals v. Polymers or ceramics

Magnetic properties

Permeability, retentivity, hysteresis loss, coercivity, intrinsic induction, etc.

Ferromagnetism – Fe, Ni, Co

Measure of response to a magnetic field

Flux density, B (B-H curve)

Importance and application of ‘hysteresis loop’

What materials? LCS Laminae in electric motors

Gravimetric – mass of materials

Density & specific gravity (used with cost)

Porosity – theoretical v. apparent

Optical properties

Important Mechanical Properties

Mechanical Properties

Stress [N/m² or Pa]

Elastic v. plastic

Elastic modulus, E

Strain

Hooke’s Law

Tensile test

Gage marks for strain measurement

Extensometer

Proportional limit, yield stress (0.2%), UTS

Ductility - % elongation, % area reduction

Mechanical Properties

Two s-e curves:

Engineering

True

Work or strain hardening

Significance of exponent

Poisson’s ratio

0.2 – 0.35

Stress-strain testing

Resilience – elastic energy absorption

Shear properties

Shear modulus

Hardness tests

Mohs, Brinell, Rockwell, Knoop, Vickers

Shore Durometer

Impact tests

Impact strength [J/m³]

NDT or DBTT

Long-term Serviceability

Endurance limit, Creep, Stress rupture

Fracture mechanics

Fracture Toughness, K_c

Manufacturing Considerations

Surface finish

Roughness, waviness

Profilometers

Cutoff width

Surface texture

Size and shape

Stock tolerances