Residual Stress Distribution Of T-joint Cross Weld Of Bridge Weathering Steel And Its Effect On Fatigue Performance

Weathering steel has the high-quality characteristics of general steel and can play the anti-corrosion performance without coating.It has received extensive attention in the construction of steel bridges in China.Welding is the main connection method of steel bridges.During the welding process,the components will experience nonuniform heating and cooling processes,resulting in large residual stress around the weld after welding.Studies have shown that welding residual stress will adversely affect the fatigue resistance of the structure.To meet the requirements of structural details and bearing capacity,complex and diverse cross welds will inevitably appear in steel bridges,and the corresponding residual stress distribution will be more complicated.Therefore,it is necessary to systematically study the residual stress distribution in cross welds and its influence on the fatigue performance of welded joints.Residual stress testing and simulation are commonly used research methods.However,insufficient data on high temperature thermal physical properties of materials is one of important reasons for inaccurate welding simulation results.At present,there is a lack of data on the high-temperature mechanical properties of weathering steel in China.It is necessary to conduct tests on the mechanical properties of bridge weathering steel at room and high temperatures.Therefore,in this thesis,the bridge weathering steel Q345 q DNH is used to study its mechanical performance parameters at room and high temperatures;for the T-joint cross weld structure with preset and no welding holes,the welding residual stress was studied by test experiments and numerical simulation methods.Then,based on the fracture mechanics method,the fatigue crack growth life of the bridge weathering steel T-joint cross weld structure considering the welding residual stress was analyzed through numerical simulation.The main works can be summarized in the following.(1)The development and application of bridge weathering steel and cross weld structure in steel bridges are introduced.The application status of cross weld structure is analyzed.It is pointed out that there is less research on the residual stress of cross weld welding,the current research status of high-temperature mechanical performance test methods,mechanical performance parameters,and high-temperature constitutive models.It is concluded that the high-temperature mechanical properties of bridge weathering steels of different countries and models have obvious differences;the research status of fatigue performance of bridge weathering steel welded structures is introduced.Analysis of research methods,consideration factors and other aspects pointed out that the fatigue performance of bridge weathering steel welded structure considering the influence of welding residual stress is relatively scarce.Comprehensive analysis points out that corresponding systematic research is urgently needed for these research deficiencies.(2)A monotonic tensile test study was carried out for the domestic weathering steel Q345 q DNH at 8 different temperatures(20 ℃ ～700 ℃),and the main mechanical performance parameters and stress-strain curve evolution law of the steel were obtained,and Q345 q DNH was established.The high-temperature constitutive relationship model provides a key data basis for thermal simulation of steel welding.(3)Designed and manufactured T-joint cross weld test specimen of bridge weathering steel Q345 q DNH with preset and no welding holes.The thickness of the base plate of the test specimen is 16 mm and the thickness of the rib is 12 mm.The welding residual stress test on the surface of the T-joint cross weld test piece was carried out by the blind hole method,and the distribution law of the residual stress in the longitudinal,transverse and overall plane was explored.(4)Based on the finite element software ABAQUS,the three-dimensional numerical simulation of the temperature field and the stress field of the bridge weathering steel T-joint cross weld specimen was carried out,and the size and specific distribution of the welding residual stress were calculated.The results of residual stress test were used to verify the simulation results and the influence of welding holes on the size and distribution of welding residual stress was discussed.(5)Through the interactive application of finite element software ABAQUS and Franc3 D,the simulation of crack propagation in T-joint cross welds of bridge weathering steel with preset and no welded holes was realized.Based on the influence of welding residual stress,the test was calculated.The fatigue life of the parts,the influence of structural changes and the introduction of welding residual stress on the fatigue performance of the specimens were discussed.The relevant research results can provide references for the structural design and fatigue design of the steel bridges.