STRESS - STRAIN RELATIONS BASIC INFORMATION
What is Stress - Strain Relations?
What is Stress - Strain Relations?
Materials
deform in response to loads or forces. In 1678, Robert Hooke published the first
findings that documented a linear relationship between the amount of force applied
to a member and its deformation.
The amount
of deformation is proportional to the properties of the material and its
dimensions. The effect of the dimensions can be normalized. Dividing the force
by the cross-sectional area of the specimen normalizes the effect of the loaded
area.
The force
per unit area is defined as the stress in the specimen (i.e., ). Dividing the
deformation by the original length is defined as strain of the specimen (i.e.,
length/original length). Much useful information about the material can be
determined by plotting the stress–strain diagram.
Figure 1.2
shows typical uniaxial tensile or compressive stress–strain curves for several
engineering materials. Figure 1.2(a) shows a linear stress–strain relationship up
to the point where the material fails. Glass and chalk are typical of materials
exhibiting this tensile behavior.
Figure
1.2(b) shows the behavior of steel in tension. Here, a linear relationship is
obtained up to a certain point (proportional limit), after which the material
deforms without much increase in stress.
On the other
hand, aluminum alloys in tension exhibit a linear stress–strain relation up to
the proportional\ limit, after which a nonlinear relation follows, as
illustrated in Figure 1.2(c).
Figure
1.2(d) shows a nonlinear relation throughout the whole range. Concrete and
other materials exhibit this relationship, although the first portion of the
curve for concrete is very close to being linear.
Soft rubber
in tension differs from most materials in such a way that it shows an almost
linear stress–strain relationship followed by a reverse curve, as shown in
Figure 1.2(e).
