C haPter 5 Material Property Charts and their Uses
154
A material feels “cold” to the touch if it conducts heat away from
the finger quickly; it is “warm” if it does not. This has something
to do with the technical attribute thermal conductivity, but there
is more to it than that; it also depends on specific heat. A measure
of this perceived coldness or warmth of a material (in the sense of
heat, not of color) is the quantity λ ρ
⋅ ⋅C p , where λ is the thermal
conductivity, ρ is the density, and C p is the specific heat. It is shown
as the other axis of Figure 5.6. The figure nicely displays the tactile
properties of materials. Polymer films and low-density woods are
warm and soft. Ceramics, stone, and metals are cold and hard. Polymers and composites lie in between.
hearing: acoustic attributes
The frequency of sound (pitch) emitted when an object is struck
relates to two material properties: modulus and density. A measure
of this pitch is used as one axis of Figure 5.7. Frequency is
not the only aspect of acoustic response; another one has to do
with damping. A highly damp material sounds dull and muffled;
one with low damping rings. Acoustic brightness—the inverse
of damping—is used as the other axis of Figure 5.7. It groups
materials that have similar acoustic behavior.
Bronze, glass, and steel ring when struck, and the sound they emit
has, on a relative scale, a high pitch. These materials are used to
make bells. Alumina, on this ranking, has the same bell-like qualities. Rubber, foam, and many polymers sound dull, and, relative
to metals, they vibrate at low frequencies; they are used for sound
damping. Lead, too, is dull and low-pitched; it is used to clad buildings for sound insulation.
5.2 Using Charts to seleCt
translation, sCreening, ranking,
anD DoCUMentation
Selection involves seeking the best match between the attribute
profiles of the materials—bearing in mind that these must be mutually compatible—and those required by the design. The strategy,
applied to materials, is sketched in Figure 5.8. The first task is that of
translation: converting the design requirements into a prescription
for selecting a material. This proceeds by identifying the constraints
that the material must meet and the objectives that the design must
fulfill. These become the filters; materials that meet the constraints
154
A material feels “cold” to the touch if it conducts heat away from
the finger quickly; it is “warm” if it does not. This has something
to do with the technical attribute thermal conductivity, but there
is more to it than that; it also depends on specific heat. A measure
of this perceived coldness or warmth of a material (in the sense of
heat, not of color) is the quantity λ ρ
⋅ ⋅C p , where λ is the thermal
conductivity, ρ is the density, and C p is the specific heat. It is shown
as the other axis of Figure 5.6. The figure nicely displays the tactile
properties of materials. Polymer films and low-density woods are
warm and soft. Ceramics, stone, and metals are cold and hard. Polymers and composites lie in between.
hearing: acoustic attributes
The frequency of sound (pitch) emitted when an object is struck
relates to two material properties: modulus and density. A measure
of this pitch is used as one axis of Figure 5.7. Frequency is
not the only aspect of acoustic response; another one has to do
with damping. A highly damp material sounds dull and muffled;
one with low damping rings. Acoustic brightness—the inverse
of damping—is used as the other axis of Figure 5.7. It groups
materials that have similar acoustic behavior.
Bronze, glass, and steel ring when struck, and the sound they emit
has, on a relative scale, a high pitch. These materials are used to
make bells. Alumina, on this ranking, has the same bell-like qualities. Rubber, foam, and many polymers sound dull, and, relative
to metals, they vibrate at low frequencies; they are used for sound
damping. Lead, too, is dull and low-pitched; it is used to clad buildings for sound insulation.
5.2 Using Charts to seleCt
translation, sCreening, ranking,
anD DoCUMentation
Selection involves seeking the best match between the attribute
profiles of the materials—bearing in mind that these must be mutually compatible—and those required by the design. The strategy,
applied to materials, is sketched in Figure 5.8. The first task is that of
translation: converting the design requirements into a prescription
for selecting a material. This proceeds by identifying the constraints
that the material must meet and the objectives that the design must
fulfill. These become the filters; materials that meet the constraints