Mechanical Properties and Constitutive Model of Steel Under Temperature–Humidity Cycles

Through alternating high–low temperature and humid heat tests, six sets of different humidity cycle numbers were applied to Q235B low-carbon steel and Q345B low-alloy steel. Monotonic tensile tests were conducted to compare the differences in monotonic performance degradations. The influence of humidity cycle numbers on the hysteretic and fatigue performance of Q235 steel was investigated through cyclic loading tests. A cyclic constitutive model based on the mixed hardening model was established and validated. The results show that the humid heat environment causes corrosion of the steel, and the degree of corrosion follows a power-law relationship with the number of humid heat cycles. Under monotonic loading, as the number of humid heat cycles increases, the strength and deformation performance of both steels degrade linearly, with Q345 low-alloy steel exhibiting more significant performance deterioration. The corrosion damage induced by the humid heat environment greatly reduces the low-cycle fatigue life of Q235 steel, and the more severe the corrosion, the lower the fatigue life. However, there is no significant effect on the development of the hysteretic curve shape. Under variable amplitude cyclic loading, as the corrosion degree increases, the hysteretic energy dissipation and energy dissipation rate continuously decrease. The two-segment backbone curve considering mass loss rate and the material hardening parameters based on the mixed hardening model can accurately describe the hysteretic characteristics of Q235 low-carbon steel under the humid heat environment.

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