中文摘要：

直缝焊管广泛应用于汽车车身管状零件液压成形中,焊接区影响着焊管塑性变形规律,准确评价焊管缩颈或破裂现象是工程上倍受关注的问题。基于金相分析法和显微硬度测量法分析高频感应焊管的结构特征,并根据液压成形条件下高频感应焊管的变形特点,提出一种用于计算直缝焊管液压成形极限的理论方法。基于该方法,选用Swift硬化方程和Hill屈服准则推导出直缝焊管液压成形极限理论预测模型,在已知焊管（包含焊接区和基体区）材料性能参数条件下可获得直缝焊管液压成形极限图。运用此理论预测模型,计算出QSTE340高频感应焊管的液压成形极限图。成形极限的计算结果与试验对比表明,二者吻合较好,这证明所建立的直缝焊管液压成形极限的理论预测模型是正确的。

英文摘要：

Welded tubes have been widely used to manufacture tube hydroformed parts in the automotive industry.The non-uniform plastic deformation is caused by the weld zone,thus the accuracy evaluation for necking or fracture of seamed tube hydroforming is a problem which catches much concern in engineering.Based on metallographic analysis and microhardness testing methods,the structure and the forming characteristics of electrical resistance welding（ERW） welded tube are analyzed.A novel theoretical method is developed to predict the forming limit diagram（FLD） for welded tube hydroforming considering the unique features of seamed tube hydroforming.Based on this theoretical method,a new prediction model for forming limit of welded tube hydrforming is proposed using Swift hardening equation and Hill yield criterion.The FLD for welded tube hydroforming can be calculated after ascertaining the properties of welded tube,comprised of weld zone metal and base metal.Based on this prediction model,the FLD for an ERW welded tube of QSTE340 is calculated by programming.Good correlation between the theoretical predicting result and experimental data is indicated,and prove the validity and reliability of this theoretical model.