Fundamental Engineering Concepts - Mathematics and Statistics for the Environment - page 240

Force

Force

(A) (B)

FIGURE 11.8 (A) Stress is measured in terms of the applied load over the area. (B) Strain is expressed in
terms of amount per square inch.

scope of this text, but we do include a few here that are pertinent to the environmental profession.
Many of the engineering terms defined below are from Heisler (1998), Tapley (1990), and Giachino
and Weeks (1985), all of which we highly recommend and should be standard reference texts for
environmental engineers.

Mechanics —Branch of science that deals with forces and motion.
Rupture —The ultimate failure of tough ductile materials loaded in tension.
Buckling —Failure mode characterized by the sudden failure of a structural member subjected
to high compressive stresses, where the actual compressive stress at the point of failure is
less than the ultimate compressive stresses that the material is capable of withstanding.
Stress —The internal resistance a material offers to being deformed; it is measured in terms of
the applied load over the area (see Figure 11.8A)
Strain —Deformation that results from a stress; it is expressed in terms of the amount of defor-
mation per square inch (see Figure 11.8B).
Corrosion —The breaking down of essential properties in a material due to chemical reac-
tions with its surroundings.
Intensity of stress —Stress per unit area, usually expressed in pounds per square inch; it is
the result of a force of P pounds producing tension, compression, or shear on an area of A
square inches, over which it is uniformly distributed. The simple term stress is normally
used to indicate intensity of stress.
Creep —The tendency of a solid material to slowly move or deform permanently under the
influence of stresses.
Ultimate stress —The greatest stress that can be produced in a body before rupture occurs.
Allowable stress or working stress —The intensity of stress that the material of a structure or
a machine is designed to resist.
Elastic limit— The maximum intensity of stress to which a material may be subjected and
return to its original shape upon the removal of stress (see Figure 11.9).
Yield point— The intensity of stress beyond which the change in length increases rapidly with
little (if any) increase in stress.
Fracture —Local separation of an object or material into two or more pieces under the action
of stress.

Force

FIGURE 11.9 Elasticity and elastic limit; a metal has the ability to return to its original shape after being
elongated or distorted, unless it reaches its maximum stress point.