Corrosion Damage Of Q690E Steel Plate And Mechanical Properties After Corrosion

With the rapid expansion of the steel structures in newly built buildings and the promulgation of the design code of high strength steel,the application of domestic high strength steel plate will be more and more extensive.However,if these structures served in a harsh environment,they will expose to a severe threat of corrosion damage.Corrosion would induce the uniform and non-uniform damage on the structural members,and would further cause the degradation of strength and deformability.Compared with ordinary strength steel structures,the section size of the high strength steel member is often smaller,so it will be more sensitive to corrosion damage.Therefore,it is significant to systematically conduct research on the corrosion characteristics of high strength steel plate and research on the mechanical properties of high strength steel plate before and after corrosion.This research concentrated on the Q690 E steel plate,and the corrosion damage and the mechanical properties of the steel plate after corrosion were systematically studied by means of experimental investigations and theoretical analysis.The main contents of this thesis are as follows:(1)Q690E steel plate specimens were subjected to the accelerated salt spray corrosion tests with different experimental parameters,and the average corrosion rate was calculated.The experimental results showed that the composition of the corrosive media,salt spray settling direction,chemical composition and microstructure of the steel,stress state et al.could influence the corrosion rate.After cleaning the corrosion products,the 3D morphology of the corroded surface was extracted and the corrosion damage parameters were defined.The results revealed that the surface roughness and mass loss ratio showed a positive linear correlation.Based on the 3D morphology of the corroded surface,the characteristics of non-uniform corrosion depth were analyzed,and a method for separating corrosion damage components was proposed.It was concluded that the non-uniform corrosion depth conformed to the type II extreme value distribution.At the initial stage of corrosion,there was only the nonuniform corrosion component.As the corrosion degree increased,both the uniform and the non-uniform corrosion components gradually increased.However,at the later stage of corrosion,the proportion of uniform corrosion component exceeded the nonuniform corrosion component.(2)The monotonic tensile tests were carried out on the Q690 E steel plate before and after corrosion,respectively.The tensile properties of the steel plate were obtained,which included nominal yield stress,nominal ultimate stress,yield ratio and final elongation ratio.The influence of the total corrosion damage and corrosion components on the tensile properties was investigated,and the degradation laws were established.It showed that the monotonic tensile properties of Q690 E steel plate degraded linearly with the increase of total corrosion damage.With the same corrosion degree,the elongation loss ratio was much higher than the strength loss ratio.The strength degradation was mainly caused by uniform corrosion damage,while the deformability degradation was mainly caused by non-uniform corrosion damage.(3)The axial cyclic loading tests were conducted on the Q690 E steel plate before and after corrosion,respectively.The fatigue life,cyclic softening behavior and the energy dissipation properties were studied.The influence of corrosion damage on the cyclic properties of Q690 E steel plate was analyzed.The experimental results showed that the corrosion damage would lead to the reduction of the low cycle fatigue life,the degradation and shrinkage of the hysteresis curve.The rough surface caused by corrosion would lead to the earlier initiation of cracks and result in the increase of the number of cracks,which would affect the strain softening rate.Besides,the cyclic constitutive model of the Q690 E steel plate was established and verified by the experimental data,which was based on the nonlinear combined hardening model.(4)According to the stochastic characteristics of the non-uniform corrosion depth at different corrosion degree,a mathematical model of random corrosion damage of Q690 E steel plate was proposed.Considering the randomness of corrosion damage,the corresponding FE models were established and verified by the experimental results.Furthermore,based on the method,the compression and shear properties of Q690 E steel plate after corrosion were analyzed and the stochastic characteristics of the ultimate strength of the plates were also studied.The results showed that under the same corrosion degree,the ultimate strength of the plate conformed normal distribution,and the sensitivity of different plate to corrosion damage was different.