Properties of MetalsDOE-HDBK-1017/1-93STRESSPressure stressesare stresses induced in vessels containing pressurized materials. Theloading is provided by the same force producing the pressure. In a reactor facility, thereactor vessel is a prime example of a pressure vessel.Flow stressesoccur when a mass of flowing fluid induces a dynamic pressure on aconduit wall. The force of the fluid striking the wall acts as the load. This type ofstress may be applied in an unsteady fashion when flow rates fluctuate. Water hammeris an example of a transient flow stress.Thermal stressesexist whenever temperature gradients are present in a material.Different temperatures produce different expansions and subject materials to internalstress. This type of stress is particularly noticeable in mechanisms operating at hightemperatures that are cooled by a cold fluid. Thermal stress is further discussed inModule 3.Fatigue stressesare due to cyclic application of a stress. The stresses could be due tovibration 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 andcyclic 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 ofinternal load. They are known as tensile, compressive, and shear. Figure 1 illustrates thedifferent types of stress. Mathematically, there are only two types of internal load becausetensile and compressive stress may be regarded as the positive and negative versions of thesame type of normal loading.Rev. 0Page 3MS-02
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