The Effect Of Pitting Corrosion On Fatigue Performance Of Riveted Components Under Residual Stress Of Hot Riveting

The riveted steel truss bridges are very representative steel bridge structures from the 50 s to the 60 s of the last century and have been widely used at home and abroad.Most of these bridges have been in service for more than 50 years.Different from newly built bridges,due to the limitations of time,understanding,economic conditions,etc,the corrosion resistance of existing riveted bridge steels is poor and the single maintenance method leads to the deterioration of structural performance.The existing riveted steel truss bridges have complicated riveting stress fields at the riveting holes due to their unique riveting characteristics,and their fatigue-prone initiation points are difficult to determine.The stress concentration generated by corrosion pits such as pitting and erosion further accelerates the initiation and expansion of crack,leading to premature failure of components,shortening the fatigue life of the structure,and seriously threatening the service safety of existing riveted steel truss bridges.How to determine the true initial stress state of the riveted member before loading,determine the location of fatigue damage initiation and evaluate the pitting deterioration effect of the fatigue performance of the riveted member is the basis for reducing the safety risk of the structure and significantly improving its service quality.However,there are few studies on the effect of hot riveting process on the stress field around the riveting hole.For the fatigue performance evaluation of the existing riveted steel bridge,the residual stress field distribution under the action of the hot riveting process and the influence of the mesosurface characteristics of the riveted structure corrosion on the fatigue performance are not considered,and there is a lack of clear physical meaning.This paper combines the hot riveting process to study the effect of corrosion pits with different characteristics on the stress concentration effect and structural fatigue performance.The main research contents and conclusions are as follows:(1)Based on the actual situation,the whole process of the hot riveting process was analyzed.The whole process was divided into four stages.Based on the four stages of the hot riveting process,the simplified finite element modeling method was used to simulate the hot riveting by applying a certain impact velocity to the rivet drive head stamping process,After in-depth research and repeated attempts on key factors such as the selection of elements,the division of the grid,the setting of interactions and constraints,and finally the thermalmechanical sequential coupling method was used to calculate the temperature field and stressstrain field,then,the correctness of the method is verified based on the temperature and strain changes measured by experiments.(2)Based on the correct modeling method,the ABAQUS software is used to establish the finite element model of the riveted member studied in this paper and the temperature field is calculated.Based on the temperature field,the hot riveting stress field is calculated and analyzed,mainly analyzed the change law of axial stress and longitudinal stress.The research shows that the riveting stamping and cooling process have a significant effect on the stress distribution of the riveted plate under the rivet head,making it axially and longitudinally under compression,the axial compression stress value can reach 320 MPa,and the longitudinal compression stress is 85 MPa.After external load is applied to the structure,the rivet hole is a fatigue vulnerable point,which is easy to produce initial fatigue cracks.(3)According to the survey results of the Niujiaotuo Bridge on the Jialing River in Chongqing,the characteristic parameters of pitting corrosion were determined.Based on the analysis results of residual stress in the hot riveting process,the riveting structure model with single pitting and multi-pitting corrosion considering the residual stress was established using ABAQUS.The results show that under load,the stress concentration problem at the pitting area is prominent,the local stress is higher,the high stress area is distributed in a stripe perpendicular to the external load direction,and the maximum stress position is located at the edge of the pitting pit.Under a single pitting condition,the stress concentration factor is related to the pitting depth,radius,and position;under multiple pitting conditions,the stress concentration factor is mainly related to the angle and relative distance between the pitting corrosion.(4)Based on the discussion of the influencing factors of stress concentration coefficients,the relationship between single pitting depth,radius,position and stress concentration coefficient is quantified,the formulas for single pitting stress concentration,pitting depth-todiameter ratio and pitting position are derived.On this basis,using the method of parameter normalization,the formula for the two pits stress concentration factor is derived,and a flow chart for predicting the size of the two pits stress concentration factor is derived.Finally,according to the single pit and two pits stress concentration coefficient formulas,the stress concentration factor at the pitting on the riveted structure can be predicted.Through comparative analysis with the stress concentration factor at the riveting hole,the fatigue damage initiation location of the structure are judged and the fatigue performance of the riveted structure is evaluated based on the nominal stress method.