Page 109 - Manufacturing Engineering and Technology - Kalpakjian, Serope : Schmid, Steven R.

Physical Properties

of Materials

3.| Introduction 88
3.2 Density 89 ° Physical properties can have several important roles in the selection, process-
3.3 MeltingPoint 92 ing, and use of materials.
3.4 Specific Heat 92 ° These properties are key factors in determining a material’s suitability for spe-
3.5 Thermal Conductivity 93 cific applications, especially when considered simultaneously with mechanical
3.6 Thermal Expansion 93
properties.
3.7 Electrical, Magnetic, and
Optical Properties 94 ° Strength-to-weight and stiffness-to-weight ratios, as examples, are discussed
3.8 Corrosion Resistance 95
in the context of lightweight designs, a key consideration in aerospace and
EXAMPLE:
automotive industries.
3.| Selection of Materials ° Thermal, electrical, magnetic, and optical properties are then presented.
for Coins 96
° The importance of corrosion and corrosion-resistant materials are described.
° Design and manufacturing implications of all of these properties are consid-
ered, with various specific examples given.

3.l Introduction
Why is electrical wiring generally made of copper? Why are aluminum, stainless
steel, and copper so commonly used in cookware? Why are the handles of cookware
usually made of wood or plastic, while other types of handles are made of metal?
What kind of material should be chosen for the heating elements in toasters? Why
are the metallic components in some machines being replaced with ceramics? Why
are commercial airplane bodies generally made of aluminum, and why are some air-
plane components being replaced gradually with those made of various composite
materials, including reinforced plastics?
It is apparent from these questions that one important criterion in material
selection is consideration of physical properties, such as density, melting point,
specific heat, thermal conductivity, thermal expansion, electrical and magnetic prop-
erties, and resistance to oxidation and corrosion. Combinations of mechanical and
physical properties, such as the strength-to-weight and stiffness-to-weight ratios of
materials, are equally important, particularly for aircraft and aerospace structures.
Also, high-speed equipment such as textile and printing machinery, and forming and
cutting machines for high-speed operations, require lightweight components to re-
duce inertial forces and thus keep machines from excessive vibration. Several other

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