Properties of high-strength container steels under repeated static loads
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With the safety factor usually used, calculated from the yield strength, high-strength container steels accumulate substantial plastic deformation or undergo brittle fracture as the result of repeated loading.
Repeated static loading that induces cumulative plastic deformation equal to that allowed for in the design is lower than the corresponding value for static conditions and depends greatly on the number of loading cycles, decreasing with increasing numbers of cycles.
Reduction of the level of repeated static loads can lead to the development of plastic deformation exceeding the static level in some materials and favor localization in others.
Preliminary repeated static loading increases the resistance to plastic deformation at later higher loads and thus the durability of the meterial.
Strengthened steel 1Kh18N9T (laboratory samples) are not suceptible to brittle fracture when subjected to repeated static loading; plastic deformation not exceeding the static is allowable; at the same relative level of repeated static loading (σr−s/σb) steel 1Kh18N9T accumulates less plastic deformation, and has a correspondingly higher durability, than steel 5KhNM. It is assumed that the use of steel 1Kh18N9T for containers instead of 5KhNM will make it possible to raise the operating stress by 50%, with an increase of the working life by 50–100%.
KeywordsPlastic Deformation Yield Strength Static Loading High Load Static Level
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