In operation, crankshafts are generally subjected to torsional stress and bending stress due to self-weight or
weights of components or possible misalignment between journal bearings. Thus, these rotating components
are susceptible to fatigue by the nature of their operation and the fatigue failures are generally of the torsional
and rotating-bending type. Fatigue failures start at the most vulnerable point in a dynamically stressed area
particularly where there is a stress raiser. The stress raiser may be mechanical or metallurgical in nature, or
sometimes a combination of the two. Mechanical stress raisers are non-uniformities in the shape of the crankshafts
such as step changes in diameter, sharp corners and surface discontinuities like notches and machining
marks etc. Metallurgical stress raisers may be quench cracks, corrosion pits, gross metallic inclusions, brittle
second-phase particles, etc. [3]. Also, the microstructure of the crankshaft material plays a vital role not only
in the initiation of fatigue failures but also during the progressive growth of the fatigue crack to cause failure
of the component.
In operation, crankshafts are generally subjected to torsional stress and bending stress due to self-weight orweights of components or possible misalignment between journal bearings. Thus, these rotating componentsare susceptible to fatigue by the nature of their operation and the fatigue failures are generally of the torsionaland rotating-bending type. Fatigue failures start at the most vulnerable point in a dynamically stressed areaparticularly where there is a stress raiser. The stress raiser may be mechanical or metallurgical in nature, orsometimes a combination of the two. Mechanical stress raisers are non-uniformities in the shape of the crankshaftssuch as step changes in diameter, sharp corners and surface discontinuities like notches and machiningmarks etc. Metallurgical stress raisers may be quench cracks, corrosion pits, gross metallic inclusions, brittlesecond-phase particles, etc. [3]. Also, the microstructure of the crankshaft material plays a vital role not onlyin the initiation of fatigue failures but also during the progressive growth of the fatigue crack to cause failureof the component.
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