The Study On The Welding Deformation Simulation Method Of Large Scale Structure By Plastic Strain Mapping

Welding is widely used in the manufacturing field such as aircraft,ships,bridges,and trains.Precise and fast prediction of the stress and deformation is the key of the manufacturing of the large-scale welded structure.For a long time,the mainstream simulation algorithm for the stress and deformation prediction of the large-scale welded structure have always faced an international problem,which is difficult to balance accuracy and efficiency: The thermal-elastic-plastic algorithm has high precision,but the efficiency is very low.The inherent strain algorithm has high efficiency,but the accuracy is low,and the algorithm is difficult to be applied to complex structure.Aiming at this problem,the paper established the technical route of welding deformation simulation for the complex structure based on the plastic strain mapping algorithm.In this paper,the key theoretical and technical problems such as precise plastic strain solution,mapping error control,mathematical modeling of welding sequence,and accurate simulation of fixture and holding force were solved.Different from the international mainstream algorithm,a fully independent property commercialization simulation software has been developed,and make it possible to solve the large-scale complex thick plate structure welding deformation problem on the ordinary PC machine.The main contents are as follows:1)Based on the energy conservation principle and the quasi-steady-state molten pool,the CFD(Computational Fluid Dynamics)-FEM(Finite Element Method)heat source model was proposed.Without heat source calibration,the prediction of the weld seam of the high energy beam welding based on the physical process is realized by the new heat source.Based on the sequential coupling,the finite element solution format of the thermo-elasticplastic algorithm was proposed.And based on the Newton-Raphson iteration method,the nonlinear solution strategy was established,which reduces the stress oscillation of the firstorder tetrahedral element.Taking electron beam welding of titanium alloy as an example,an agreement between the simulated weld seam and the experiment result was obtained by using the new heat source,and the error is about 5%.For the first time,the stress oscillation which is caused by keyhole oscillation is reflected.This model provides an accurate calculation model for the plastic strain prediction.2)For the first time,the error source of the plastic strain mapping is proved theoretically.Based on the conservation of the load and moment of the plastic strain,the error control criterion was proposed in this paper.A high-efficiency algorithm for largescale welding deformation based on plastic strain mapping was created and realized.Compared with the thermal-elastic-plastic algorithm,the deformation error is controlled within 10%.Compared with the inherent strain algorithm,this algorithm maintains the similar efficiency and can be applied to more complex welded structure.3)Based on the weld-base model and the element activation algorithm,an accurate modeling method was proposed.The modeling method considered the welding sequence based on real-time stiffness of the structure.The solution format the fixture boundary condition and the boundary force were proposed.The simulation method for the welded structure considering the welding sequence and the fixtures are established.Taking the typical welded structure as an example,the validity and accuracy of the algorithm are verified.Compared with the traditional shell element algorithm reported in the literature,the algorithm is more consistent with the measured results,and more general to complex structures.4)Based on CAE(Computer-Aided Engineering)design concepts and the C++ development platform,the finite element analysis software named INTEWELD was designed and developed,which has all independent intellectual property rights.Verification of the effectiveness of the analysis software by complex structure was carried out.Taking a laser-welded structure in an aircraft as an example.The length of the structure is around 1 m.The results show that the simulated deformation results are completely consistent with the measured results,and the maximum of the error is 0.3 mm.The software obtained a single solution for the welding deformation of tens of millions finite element meshes in an ordinary workstation within 1 hour for the pipe structure.The error between the simulated deformation and the measured reuslts is within 10%.By the software,different deformation of the different welding sequence was simulated,and the results show that the software can provide the digital simulation tools for the welding process optimization...