Beams are structural members designed to support loadings applied
perpendicular to their longitudinal axes. Because of these loadings, beams
develop an internal shear force and bending moment that, in general, vary from
point to point along the axis of the beam. Some beams may also be subjected to
an internal axial force; however, the effects of this force are often neglected
in the design, since the axial stress is generally much smaller than the
stresses developed by shear and bending. A beam that is chosen to resist both
shear and bending stresses is said to be designed on the basis of strength.
The stress analysis
of a beam generally neglects the effects caused by external distributed
loadings and concentrated forces applied to the beam. These loadings will
create additional stresses in the beam directly under the load. Notably, a
compressive stress will be developed, in addition to the bending stresses and
shear stresses discussed previously.
When an engineer is
faced with the problem of design using a specific material, it becomes
important to place an upper limit on the state of stress that defines the
material’s failure. If the material is ductile, failure is usually specified by
the initiation of yielding, whereas if the material is brittle, it is specified
by fracture. These modes of fracture are readily defined if the member is
subjected to a uniaxial state of stress, however, if the member is subjected to
biaxial or triaxial stress, the criterion for failure becomes more difficult to
establish.
Shaft that could bear a 200 lbs. person on the pedals would be of for example like this and would be aptly suitable for mini stepper desgining.
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