A Study On The Axial Compression Ultimate Strength Of Circular Pipe Components Under Combined Damage Of Cracks And Pitting

The application of steel structures in various projects is becoming increasingly widespread.In marine environments,it is highly susceptible to corrosion damage,with pitting corrosion being the most common type.Under cyclic loads such as wind and waves,components are prone to crack initiation at corrosion pits.The overall failure of a structure is often caused by the local or overall failure of a certain component.Therefore,accurate assessment of the ultimate strength of components in corrosive environments is crucial for the overall failure behavior of structures.This article investigates the influence of cracks,pitting corrosion,and their combined damage on the axial compressive ultimate strength of circular tube components through numerical simulation.The influence laws of cracks and pitting corrosion were discovered,and the ways in which cracks and pitting corrosion affect the strength of circular pipes were elucidated.The feasibility of strength prediction methods for inclined crack damaged circular pipes and joint damaged circular pipes was analyzed.The strength prediction formulas for damaged circular pipes were developed using the minimum cross-sectional area loss rate(R_max)and corrosion volume loss rate（DOV）as variables,respectively.The main work is as follows:（1）Establish a circular pipe model for cracks and pitting corrosion based on the study of circular pipe components.Firstly,the mesh convergence of the model was analyzed and the mesh size was determined under different damages;The research on the influence of crack tip and initial defects shows that the deformation of the semi-circular crack tip is relatively gentle,and the influence of different initial defects on the strength of the circular tube is not significant.Then,the reported experiments were used to validate the finite element model,and the results showed that the maximum validation error of the crack model was only-2.2%,while the maximum validation error of the pitting model was 3.1%.Moreover,a high degree of consistency was demonstrated in the failure mode of the damaged circular tube,indicating the correctness of the finite element model in this study.（2）The study investigated the influence of crack length,position,and angle on the strength of circular pipes.The results showed that the longer the crack,the closer it is to the middle of the pipe,and the smaller the crack angle,the more severe its ultimate strength degradation.When the crack length in the middle of the pipe is twice the pipe radius and the angle is 0°,the maximum strength degradation is up to 28.5%.In the study of pitting damage in another type of damage,the influence of pit parameters on the ultimate strength of circular pipes is studied.The results indicate that the corrosion volume loss rate（DOV）can better reflect the variation pattern of the ultimate strength of circular pipes,with the most severe degradation of pipe strength reaching 32.4%under random pitting DOV of 12%.Under the same DOV,the strength degradation of randomly pitting damaged circular tubes is 8.6%higher than that of regular pitting.（3）By studying the effects of cracks and pitting corrosion in joint damage.The results indicate that when the circular tube component is subjected to pitting corrosion damage,the influence law of cracks is similar to that of a single crack on the circular tube.The combined damage of regular pitting and cracking causes a greater strength weakening of circular pipes than the combined damage of random pitting and cracking.Analyzing its causes,it was found that the cross-sectional weakening caused by the overlapping of deep and parallel regular pits and cracks is more severe than that caused by random pitting and crack overlapping.Research also shows that under combined damage,there is no significant difference in the strength variation of circular pipes with different average values of pit depth;The larger the standard deviation of depth,the more severe the weakening of the ultimate strength of the circular tube.（4）Regardless of whether the circular tube is subjected to pitting damage or not,the strength of the inclined cracked tube can be predicted using the projection length towards the cross-sectional direction of the circular tube.In this simplification,over 95%of the circular tube components have an error within 5%.The strength degradation of a circular tube caused by combined damage is not equal to the sum of the strength degradation caused by the two alone,especially the high pitting strength.The combination of the two will underestimate the degradation of the ultimate strength of the circular tube,with a maximum underestimation of8.4%.In contrast,with Rmax as the variable and the strength formula developed through parameter fitting to evaluate the strength of damaged circular pipes,nearly 84%of component strength prediction errors are within-7.0%to 9.0%.The strength formula with DOV as the variable shows that nearly 100%of component strength prediction errors are within-6.0%to6.0%.At the same time,using formulas to predict existing experimental results and the results of different sizes of circular tubes in this article,it was found that using corrosion volume loss rate can more accurately evaluate the ultimate strength of circular tubes.