Study On The Temperature Field And Residual Stress Distribution Around Butt Welding Joint Of Steel Plate Through Whole Weilding Process

Welding is widely used for steel component connection in various industry fields such as shipbuilding,automobile,high-speed rail,and aerospace engineering.However,the high welding residual stress and distortion are produced after welding due to local heating and cooling in welding process.The welding residual stress not only causes dimensional error,but also adversely affects fatigue strength,structural stability,and service life and so on.Therefore,it is important to quantitatively analyze,predict and simulate the magnitude and distribution of temperature and residual stress around the connection joint in the welding process.In order to investigate various welding parameter influences on the whole process temperature field and residual stress field around the butt welding joint of steel plates,the heat source subroutine based on double ellipsoid heat source model was developed by using Fortran language.Using ABAQUS software as the platform,the solder filling of butt welding joint was simulated by using the model change technology.A finite element model considering thermal-elastic-plasticity was established,which was employed to numerically analyze the influence of plate thickness,welding speed,number of welding layers and groove type on temperature and residual stress around the weld joint.In this thesis,all specimens were welded by using CO₂ gas shielded welding technology.The residual strain distribution form of the scattered speckle image on the back side of the welded steel plate was investigated by using digital image correlation method optical method,which provided a certain experimental basis for the optical instrument to measure the strain distribution and a theoretical basis for improving the butt welding temperature field and residual stress field of steel plates.It can be concluded from the results of experiment and numerical analysis that:?1?The digital image correlation technology can better reflect the residual strain curve of the back side of the steel plate,which verify the validity and accuracy of the numerical simulation method.?2?During the welding process,the welding temperature field forms a spindle-shaped band distribution with a certain temperature gradient from the center of the heat source.The front end isotherm of the welding heat source is dense and the temperature gradient is large.The back end isotherm of the heat source is sparse,and the temperature gradient is small.?3?When the weld starts to weld,the temperature rises sharply around the welding joints,but it gradually becomes stable with the movement of the welding heat source,forming a quasi-steady temperature field.When the welding heat source is removed,the peak temperature rapidly declines.When the temperature is about100?,the descending speed begins to become extremely slow.?4?The peak temperature of the weld center is inversely proportional to the welding speed and proportional to the welding heat input.?5?With the increase of plate thickness,welding speed or the number of weld passes,the peak temperature of the characteristic point is decreasing in the parallel direction to the welding line and the temperature difference is decreasing.The peak temperature of the characteristic point is also decreasing in the perpendicular direction to the welding line,but the temperature difference is increasing.?6?The distribution of residual stress field after welding is basically"lantern"pattern.The influence range of residual stress at both ends of the weld is narrower and the stress gradient is larger.The influence range of residual stress in the middle of the weld is wider and the stress gradient is smaller.?7?There are certain distribution forms of residual stress on different paths:in the direction perpendicular to the weld,the longitudinal residual stress is generally tensile stress,which is distributed in a“several”shape,and the transverse residual stress is tensile stress as a whole,showing an M-shaped distribution.In the direction of the weld,the longitudinal residual stress is expressed as compressive stress,which is W-shaped or U-shaped.The transverse residual stress is generally tensile stress and is inverted U-shaped.?8?With the increase of plate thickness,welding speeds or number of welding layers,both residual tensile stress and compressive stress decrease.?9?Compared to the X,K,V groove butt welding of steel plates,the welding residual stress of the X-shaped groove is the smallest and the V-shaped groove is the largest.The X-shaped and K-shaped groove welding adopts the symmetric welding sequence or not,which has little effect on the residual stress around the welding joints.The asymmetric welding groove is slightly better than the symmetric welding relatively.