103
and pressure. A different type of volume defect is the cracks formed
during heating and cooling cycles or during formability processes.
Finally, welding defects can be formed during welding procedures due to the fact that the heat generated during welding is not
uniform. As a consequence, a region affected by the heat is produced, where the properties change gradually away from the heat
source.
4.3 MeChaNiCal Behavior
stress, strain, stiffness, and strength
Stress is something that is applied to a material by loading it.
Strain—a change of shape—is the material’s response. It depends
on the magnitude of the stress and the way it is applied—the mode
of loading. Ties carry tension; often they are cables. Columns carry
compression; tubes are more efficient as columns than are solid
rods of similar areas because they don’t buckle as easily. Beams carry
bending moments. Shafts carry torsion. Pressure vessels contain a
pressure. Often they are shells: curved, thin-walled structures.
Stiffness is the resistance to change of shape that is elastic, meaning
that the material returns to its original shape when the stress is
removed. Strength is its resistance to permanent distortion or total
failure. Stress and strain are not material properties; they describe
a stimulus and a response. Stiffness (measured by the elastic
modulus E, defined in a moment) and strength (measured by the
yield strength σ y or tensile strength σ ts ) are material properties. Stiffness and strength are central to mechanical design.
The elastic moduli reflect the stiffness of the bonds that hold atoms
together. There is not much you can do to change any of this, so the
moduli of pure materials cannot be manipulated at all. If you want
to control them you must either mix materials together, making
composites, or disperse space within them, making foams.
Modes of loading
Most engineering components carry loads. Their elastic response
depends on the way the loads are applied. Usually one mode dominates, and the component can be idealized as one of the simply
loaded cases in Figure 4.29: tie, column, beam, shaft, or shell. Ties
carry simple axial tension, shown in (a) in the figure; columns do
the same in simple compression, as in (b). Bending of a beam (c)
creates simple axial tension in elements above the neutral axis (the
center line, for a beam with a symmetric cross-section) and simple
Mechanical Behavior
Figure 4.26
Sequence of events leading to the formation of an
edge dislocation.
Edge dislocation line
Figure 4.27
Tilt boundary.
Axis of tilt
Grain boundary
and pressure. A different type of volume defect is the cracks formed
during heating and cooling cycles or during formability processes.
Finally, welding defects can be formed during welding procedures due to the fact that the heat generated during welding is not
uniform. As a consequence, a region affected by the heat is produced, where the properties change gradually away from the heat
source.
4.3 MeChaNiCal Behavior
stress, strain, stiffness, and strength
Stress is something that is applied to a material by loading it.
Strain—a change of shape—is the material’s response. It depends
on the magnitude of the stress and the way it is applied—the mode
of loading. Ties carry tension; often they are cables. Columns carry
compression; tubes are more efficient as columns than are solid
rods of similar areas because they don’t buckle as easily. Beams carry
bending moments. Shafts carry torsion. Pressure vessels contain a
pressure. Often they are shells: curved, thin-walled structures.
Stiffness is the resistance to change of shape that is elastic, meaning
that the material returns to its original shape when the stress is
removed. Strength is its resistance to permanent distortion or total
failure. Stress and strain are not material properties; they describe
a stimulus and a response. Stiffness (measured by the elastic
modulus E, defined in a moment) and strength (measured by the
yield strength σ y or tensile strength σ ts ) are material properties. Stiffness and strength are central to mechanical design.
The elastic moduli reflect the stiffness of the bonds that hold atoms
together. There is not much you can do to change any of this, so the
moduli of pure materials cannot be manipulated at all. If you want
to control them you must either mix materials together, making
composites, or disperse space within them, making foams.
Modes of loading
Most engineering components carry loads. Their elastic response
depends on the way the loads are applied. Usually one mode dominates, and the component can be idealized as one of the simply
loaded cases in Figure 4.29: tie, column, beam, shaft, or shell. Ties
carry simple axial tension, shown in (a) in the figure; columns do
the same in simple compression, as in (b). Bending of a beam (c)
creates simple axial tension in elements above the neutral axis (the
center line, for a beam with a symmetric cross-section) and simple
Mechanical Behavior
Figure 4.26
Sequence of events leading to the formation of an
edge dislocation.
Edge dislocation line
Figure 4.27
Tilt boundary.
Axis of tilt
Grain boundary