夹具拘束模型在焊接过程有限元分析中的建立及应用

ESTABLISHMENT AND APPLICATION OF FIXTURE CONSTRAINT MODELS IN FINITE ELEMENT ANALYSIS OF WELDING PROCESS

夹具及垫板的拘束作用对被焊平板试样残余应力与变形的演变历程具有重要影响。将夹具和垫板作为弹塑性体包含到焊接数值模拟模型中,采用4种模型模拟夹具及垫板与被焊平板试样之间的相互作用,能够提高焊接数值模拟研究方法的科学性和准确性.数值模拟结果表明,夹具拘束作用的不同处理方式对平板试样焊后残余应力分布与变形趋势有重要影响,不同拘束条件下的平板试样残余变形模拟结果,与平板试样在自由状态下和夹具夹持状态下焊接实验获得的变形趋势均一致,在焊接过程初期阶段,平板试样上下表面的横向应力分布差异,对决定平板试样的残余变形趋势有重要影响。

The mechanical interaction between welded panel and fixture has a remarkable influence on the distribution of weld induced residual stress and distortion.Unfortunately,the influence of fixture is not generally included in conventional numerical simulations of welding process.In the present study,it is proposed that the numerical models in which the mechanical interaction between welded panel and fixture is considered as contact pair in the finite element analysis（FEA） of welding process.This could make the FEA of welding process more scientific and accurate.The fixture constraint plays an important role in accurate modeling of welding process.In the simulations,various mechanical constraint boundary conditions in welding process were thought about to establish the relationships of the normal and tangential mechanical interactions between welded panel and fixture. In Free model,the fixture restraint was not considered.In Mech model,the displacements of nodes where welded panel contacted with fixture were restricted in x,y,z directions.Hard model and Tabular model were contact models which included the fixture.In the normal direction,once welded panel and fixture were in contact,the transmitted contact pressure could be infinite in Hard model.While data pairs of contact pressure vs over-closure or clearance were specified to define a piecewise-linear relationship in the normal direction in Tabular model.A penalty friction coefficient of 0.3 was applied in tangential direction in both Hard and Tabular models.Fixture and welded panel were separated and the contact relationships were removed after the welding process in both Hard and Tabular models. The simulation results of contact models including fixture were more accurate,compared to models containing only welded panel with rigid restrictions.The distortion mode of welded panels under different fixture constraint conditions corresponded well with experimental results.The differences between the distributions of transverse stresses on top and bottom surfaces of welded panel at the beginning of welding process had a crucial influence on the distortion mode of welded panel.