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The design basis of plastic failure of pressure vessel is elastoplastic theory. The design criterion is: it can allow the stress intensity of local film stress and bending stress to have a large allowable value, that is, tolerate local plastic deformation, the pressure vessel still Will not expire.
The reason is analyzed mainly because the film stress and bending stress occur locally, even if the maximum stress reaches the limit of yield, it can only cause local yielding, but for the entire pressure vessel, most of the area is still elastic. It will fail. At this time, if it is treated by elastic failure, it will make many materials unable to exert their potential.
The so-called fatigue of the container means that the material is destroyed under the repeated alternating load, and there is no obvious plastic deformation at this time.
In the past pressure vessel design, fatigue was rarely considered as an important factor. The manufacture of pressure vessels is moving toward large-scale development, and high-strength low-alloy steels are also slowly being put into production. These materials have a high possibility of causing cracks and unknown defects in the manufacturing process, and the probability of damage due to fatigue increases. Relevant statistics show that in all the damage accidents with easy pressure, about 40% of the accidents are caused by the gradual expansion of fatigue cracks.
The typical problem of the fatigue problem of a pressure vessel is that it is subjected to a large stress, the maximum stress may even exceed the service limit of the material twice, and the number of failure cycles is relatively low. Therefore, fatigue problems are gradually being valued by people.
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