Study On The Pressure Behavior Of Steel With Multiple Pitting Damage

Ships and marine structures are inevitably subject to corrosion due to long-term exposure to harsh marine environments.Ships and marine engineering structures are mainly carbon steel and low-alloy steel,and the most common types of corrosion damage are uniform corrosion and pitting corrosion.Uniform corrosion has a large amount of corrosion loss,but because the corrosion is approximately uniform,its impact on the mechanical properties of the structure can be expected.The pitting damage has complex corrosion forms,uneven depth and location,and internal damage that is not easy to detect.The local stress concentration caused by it will not only reduce the load-bearing capacity and deformation capacity of the structure,but also change the failure mode of components,especially compression components,which will cause serious damage for marine engineering structure.In view of the above analysis,in order to study the influence of multi-pit corrosion damage on the mechanical properties and failure modes of steel specimens under compression,the following work has been done in this paper:Through the axial compression test of multi-pit corrosion damage steel,the stress-strain curves of different pitting corrosion parameters(diameter and depth),pitting distribution mode,and pitting interval are obtained.The results show that with the increase of pitting diameter and depth,the length of the yield section of the specimen is gradually reduced,and the ductility ability decreases;the ultimate strength and yield strength of the specimen are decreasing,and the yield strength is more sensitive to pitting damage.Different from the weak influence of the pitting distance on the specimen,the distribution method of pitting has a greater impact on the mechanical properties of the specimen.When the pitting corrosion is distributed in the vertical direction of the force,the degree of weakening of the mechanical properties of the specimen is much greater than the pitting corrosion is arranged along the force direction,so the volume loss rate(VLR)and DOP are not a good evaluation of the influence of pitting corrosion damage.The simplified physical model is used to derive the critical stress formula of the pitting damage variable cross-section specimen and the parameter sensitivity analysis of the failure mode transition is carried out.Under three different boundary conditions,the normalized pitting depth does not have much effect on the critical stress of the specimen.The increase of the normalized pitting diameter may cause the length coefficient of the specimen to grow nonlinearly,which leads to the specimen from strength failure to buckling failure.As the number of pitting corrosion increases,the length coefficient of the specimen will increase,the critical stress will decrease,and its ability to resist buckling failure will be further weakened.Through the comparison of various evaluation indexes of typical corrosion degree,the reasonable evaluation index of the pressure performance of the same length and multiple pit corrosion damage specimens is determined as the cross-sectional loss rate.According to the analysis of the mechanical characteristics of the test results,combined with the logarithmic analysis results of the inelastic section data in the experimental stress-strain curve,the linear exponential model of the multi-pitting damage steel with the variable cross-sectional loss rate is determined.The comparison verifies the good agreement between the model and the test results.It also provides a basis and reference for the establishment of corrosion damage mechanical models of other offshore steels.The ABAQUS software was used to carry out the numerical simulation of the pitting corrosion specimen under pressure.The comparison between the numerical results and the test results verified the authenticity and effectiveness of the two.Through numerical analysis,it is found that under the condition of axial compression,the pitting position has a certain influence on the ultimate bearing capacity of the specimen.