Research On The Experimental Characteristics Of Plastic Bending Of Welded Joints

Welding technology is widely used in marine and offshore industries.The mechanical properties of welded joints play an important role in the reliability of marine equipment.The bending experiment is an important means to evaluate the mechanical properties of welded joints.At present,three point bending is mainly used to test the bending performance of the same kind of welded joints.There are few comparative studies on the bending properties of welded joints under different bending methods.There is a great gap in the study of the bending properties of dissimilar materials welded joints.In this thesis,we study the bending properties of welded joints of the same material and dissimilar materials from different bending methods and different bending conditions.The main contents of this thesis are as follows:(1)Based on the plastic bending theory of plate material,the theoretical formula for selecting the bending diameter under ideal conditions was deduced.Then,finite element simulations were performed on two bending experimental methods for the same material welded joints.and the bending elongation,the thickness direction strain and the variation of the length direction strain under different bending conditions are obtained.Deviations between the mean value of strain in the longitudinal direction and the calculated value of the theoretical formula are all within 5%.The relationship between strain peak and flexural elongation under different bending conditions is further discussed,and the revised formula of minimum bending diameter is established.Finally,the selection criterion of the diameter of bending head in the China Classification Society’s is analyzed.It shows that the code is basically consistent with the calculated results of the bending diameter under the modified three point bending condition.However,a bending experiment using a roller bending method and a smaller bending diameter can be used to obtain more accurate inspection results.(2)Finite element analysis was performed on the three-point bending of dissimilar materials welded joints.The phenomenon of slip and sudden bending appeared at the welded joint.It showed that three point bending could not effectively evaluate the flexural performance of the dissimilar material welded joint.In addition,a group of rollers bending finite element simulation was carried out for different ends of gripping welded plate and the distance between the moving roller and the plate x.The results of finite element simulation show that The plastic deformation of welded joints is good when clamping soft materials,and the bending effect is independent of the distance x from the moving roller to the plate;There is a large gap between the welded joint and the fixed roller when the hard material is clamped,and the gap size increases linearly with the x value and is directly proportional to the yield strength difference of the two materials.Welded joints cannot be uniformly plastically deformed.(3)Roller bending experimental apparatus was developed,which mainly includes power transmission and detection device,bending device and clamping device.The device can meet the test requirements of roller bending in GB/T 2653-2008.It can change the diameter of the roller freely and the bending accuracy is 0.1° and reaches the level 1 experimental force value,and can effectively evaluate the mechanical properties of the welded joint.At the same time,stress analysis and strength check are made for the main parts,and the checking results meet the design requirements.(4)Bending experiment of ZG200-400 and E36 welded joints under different conditions were carried out with two kinds of bending testing machines.The deviation of the bending elongation of the same material welded joint under different conditions from the finite element analysis results is less than 5%,and the strain variation in the thickness direction is basically consistent with the finite element analysis results,and the correctness of the correction formula is verified.The results of the bending experiment of dissimilar materials welded joints are consistent with the results of finite element analysis,which shows that the roller bending of clamping soft material can effectively evaluate the mechanical properties of the welded joints,and the three point bending and roller bending of clamping hard material welded joints will cause bumps and slips phenomenon.