Properties of Metals
DOE-HDBK-1017/1-93
STRESS
Pressure stresses are stresses induced in vessels containing pressurized materials. The
loading is provided by the same force producing the pressure. In a reactor facility, the
reactor vessel is a prime example of a pressure vessel.
Flow stresses occur when a mass of flowing fluid induces a dynamic pressure on a
conduit wall. The force of the fluid striking the wall acts as the load. This type of
stress may be applied in an unsteady fashion when flow rates fluctuate. Water hammer
is an example of a transient flow stress.
Thermal stresses exist whenever temperature gradients are present in a material.
Different temperatures produce different expansions and subject materials to internal
stress. This type of stress is particularly noticeable in mechanisms operating at high
temperatures that are cooled by a cold fluid. Thermal stress is further discussed in
Module 3.
Fatigue stresses are due to cyclic application of a stress. The stresses could be due to
vibration or thermal cycling. Fatigue stresses are further discussed in Module 4.
The importance of all stresses is increased when the materials supporting them are flawed.
Flaws tend to add additional stress to a material. Also, when loadings are cyclic or unsteady,
stresses can effect a material more severely. The additional stresses associated with flaws and
cyclic loading may exceed the stress necessary for a material to fail.
Stress intensity within the body of a component is expressed as one of three basic types of
internal load. They are known as tensile, compressive, and shear. Figure 1 illustrates the
different types of stress. Mathematically, there are only two types of internal load because
tensile and compressive stress may be regarded as the positive and negative versions of the
same type of normal loading.
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