Study On Constitutive Model Of Corrosion-damaged Steel Under Cyclic Loading

The offshore platform in service has been corroded by seawater for a long time in the marine environment,the strength and rigidity of the steel will change,and the ability to resist external loads will also be reduced.At this time,if it is subjected to extreme cyclic loads such as earthquakes,the possibility of dangerous accidents such as collapse will greatly increase.In order to prevent the occurrence of this danger and describe the impact of corrosion damage and low-cycle fatigue coupling damage on the mechanical properties of marine steel,based on the cyclic test results of commonly used D36 steel considering different corrosion conditions(pitting corrosion or random corrosion)and loading schemes,a generalized constitutive model considering different cyclic loading systems and different corrosion degrees of steel was established.Three typical hardening models are studied,namely isotropic hardening model(NLISO),kinetic hardening model(Chaboche)and combined hardening model.The constitutive parameters calibrated by the cyclic loading test data of pitting corrosion damage steel are used to find the combined hardening model.It can simulate all the pitting corrosion conditions in the test results more ideally,and can also simulate the hysteretic performance of steel under various cyclic loading systems.However,the relationship between its parameters and the volume loss rate(VLR)of pitting corrosion is difficult to clarify,which cannot meet the various pitting corrosion degrees in general engineering practice.In order to establish a constitutive model with the degree of pitting corrosion as a variable,the hysteresis curve of steel is analyzed and the constitutive model is divided into a cyclic hardening skeleton section,an unloading section and a reloading section.The direct function relationship between it and the volume loss rate is established respectively,so that the constitutive model parameters of the steel can be obtained only by the volume loss rate of the pitting corrosion,and the hysteresis curve of the steel under the pitting degree can be simulated.The model can comprehensively consider the influence of volume loss,stress concentration and eccentricity caused by pitting corrosion on the hysteretic performance of marine steel,and has good prediction accuracy.With reference to the constitutive model of pitting corrosion damage steel,the constitutive model of random corrosion damage steel is also divided into cyclic hardening frame section,unloading section and reloading section,and a constitutive model with random corrosion volume loss rate as a variable is established.The full curve hysteresis criterion for steels with random corrosion damage is consistent with pitting corrosion damage steels and is also divided into the first loading criterion,unloading criterion,skeleton curve criterion and reloading curve criterion.Finally,the full-curve hysteresis criterion of randomly corroded steel with volume loss rate variable is obtained.