C haptEr 9 design Environments and systems
312
Variations in temperature levels can cause many materially oriented
design problems to develop. Thermal expansions and contractions,
for example, can cause thermally induced stresses to develop. It was
also noted that the actual physical properties of materials can be
markedly temperature dependent. In common steel, for example,
the ductility of the material decreases with decreasing temperature
levels. In many normal products that operate in normal environments, general levels of heat and temperatures involved can be
fairly low, and these kinds of temperature-related effects are often
not particularly critical. Materials are often selected primarily
because of their thermal conductivity levels to provide either heattransfer functions or insulation functions. Often demands placed
on these materials are multifunctional, with thermal properties
playing only one of several needed roles. A common material used
to provide thermal insulation on a handle attached to a hot object,
for example, must provide not only the needed thermal insulation
but also must be abrasion resistant and be tough against tears or
penetrations. Manufacturability and costs are clearly important as
well. Selecting materials when multiple criteria are present typically
involves tradeoffs. (See the discussion on this topic in Chapter 5.)
Design demands increase when extreme temperature environments,
either hot or cold, are present. With increasing temperatures, not
only do expansions increase but the elastic modulus can decrease,
strength can decrease, creep can increase (time-dependent deformations), and the material can even melt. Changes in electrical conductivity and other properties can also occur. Of particular importance
are the maximum service temperatures that define the maximum
usability range for a material. Other products may be expected to
work at extremely cold levels. Other effects occur here as well. A
change can occur from ductile to brittle behavior. As we will see, a
number of opportunities exist for using nanomaterials to improve
material capabilities in extreme temperature environments.
thermal Environments in spaces
As previously noted, individuals act, live, and work within tempered
spatial environments (buildings, trains, and the like). The thermal
characteristics of these environments are fundamental to maintaining conditions conducive to the health, well-being, and comfort of
occupants. Thermal environments of this type are by no means easy
to characterize and certainly go beyond only a consideration of the
temperature of the environment. Within a space, air is by no means
static. Sources of heat loss (such as through walls or windows) or
312
Variations in temperature levels can cause many materially oriented
design problems to develop. Thermal expansions and contractions,
for example, can cause thermally induced stresses to develop. It was
also noted that the actual physical properties of materials can be
markedly temperature dependent. In common steel, for example,
the ductility of the material decreases with decreasing temperature
levels. In many normal products that operate in normal environments, general levels of heat and temperatures involved can be
fairly low, and these kinds of temperature-related effects are often
not particularly critical. Materials are often selected primarily
because of their thermal conductivity levels to provide either heattransfer functions or insulation functions. Often demands placed
on these materials are multifunctional, with thermal properties
playing only one of several needed roles. A common material used
to provide thermal insulation on a handle attached to a hot object,
for example, must provide not only the needed thermal insulation
but also must be abrasion resistant and be tough against tears or
penetrations. Manufacturability and costs are clearly important as
well. Selecting materials when multiple criteria are present typically
involves tradeoffs. (See the discussion on this topic in Chapter 5.)
Design demands increase when extreme temperature environments,
either hot or cold, are present. With increasing temperatures, not
only do expansions increase but the elastic modulus can decrease,
strength can decrease, creep can increase (time-dependent deformations), and the material can even melt. Changes in electrical conductivity and other properties can also occur. Of particular importance
are the maximum service temperatures that define the maximum
usability range for a material. Other products may be expected to
work at extremely cold levels. Other effects occur here as well. A
change can occur from ductile to brittle behavior. As we will see, a
number of opportunities exist for using nanomaterials to improve
material capabilities in extreme temperature environments.
thermal Environments in spaces
As previously noted, individuals act, live, and work within tempered
spatial environments (buildings, trains, and the like). The thermal
characteristics of these environments are fundamental to maintaining conditions conducive to the health, well-being, and comfort of
occupants. Thermal environments of this type are by no means easy
to characterize and certainly go beyond only a consideration of the
temperature of the environment. Within a space, air is by no means
static. Sources of heat loss (such as through walls or windows) or