大型复杂铝合金构件焊接变形理论预测的基础问题研究

It is an effective way to fabricate light-weight structure through using Al-alloy and fusion welding technology. Because welding distortion is apt to occur in Al-alloy welded structures, it is very critical issue how to control and reduce welding deformation in such structures.The prediction method based on inherent strain theory has been regarded as an effective way to estimate welding deformation for large and complex structures. However, owing to lack of the database of inherent deformation in typical Al-alloy joints, this hampers the inherent strain method to predict welding deformation for Al-alloy structures. In this project, we propose a new method named inverse analysis method to obtain the inherent deformations for typical Al-alloy joints, and employ this method to establish a database for Al-alloy joints.In the new method, we only measure the coordinates at several locations before and after welding to obtain the basic deformation, and use the deformation at the measured location as known variables to calculate equivalent inherent deformation components along welding line. In this project, we will use thermal-elastic-plastic finite element method to investigate the distributing feature of welding inherent deformations along welding line in typical joints. Meanwhile, we will propose a simple model which can be used for engineering analysis to describe the equivalent inherent deformation. In addition, we will used the database to predict welding deformation in a few large Al-alloy welded structures, and examine the prediction accuracy through comparing with experimental mock-ups. The results not only can be used to optimize the design of welded structure but also can be employed to make reasonable welding procedure to fabricate Al-alloy structure.

使用铝合金材料和采用焊接技术是实现产品轻量化的有效途径。由于铝合金构件焊接易产生过大变形，如何高精度地预测焊接变形是一个亟待解决的关键问题。固有应变法被认为是预测大型复杂结构焊接变形最有前途的方法，但是由于缺乏铝合金接头固有变形数据，制约了该方法的有效运用。本研究针对这一问题，提出一种获得固有变形的新途径-逆解析数值方法，并采用此方法建立典型铝合金接头固有变形数据库。该方法的核心思想是通过测量少数点的三维坐标获得测量点的基本变形特征，并作为逆解析已知条件。在提出固有变形沿焊缝方向分布的简化模型基础上，开发有限元程序来逆推接头的固有变形。本研究中，采用热弹塑性有限元法获得固有变形沿焊缝方向的分布规律并验证简化模型的妥当性；利用建立的数据库预测大型铝合金构件的焊接变形，通过模拟值和实验值的比较，确立逆解析方法并验证固有变形数据库的精度。研究成果用于大型复杂铝合金构件的结构优化和焊接工艺优化。

本研究项目以铝合金和高强度钢薄板焊接接头和结构为研究对象，开发了逆解析数值计算方法获取典型焊接接头的固有应变，利用获得的固有应变数值模拟了多种薄板焊接结构的焊接变形。.采用固有应变法可以高效地预测焊接结构的变形，但前提条件是必须已知各个接头的固有变形。通常获得固有变形的方法有两种，一种是通过实验法直接获取，另一种是基于热-弹-塑性有限元方法计算得到。本研究中核心任务之一是开发基于实验测量技术和逆向计算法来获取固有应变的新方法（逆解析法）。该方法克服了前两种传统方法的缺点，使得获取固有变形更为便捷可信。.在薄板焊接接头中，由于容易产生屈曲变形，采用逆解析法获取该情形下的固有变形有较大的困难。本研究基于固有变形分布与焊接尺寸关系的特点，借助于切割法消除屈曲变形的影响，提出了一种适用于获取薄板焊接接头固有变形的方法。在本研究中，采用基于弹性有限元的固有应变和热-弹-塑性有限元方法数值模拟了铝合金及高强度钢薄板大型焊接结构的焊接变形。.此外，本项目对曲面结构的扭转变形机理进行了分析，并基于数值模拟结果和结论提出了控制扭转变形的方案。本研究开发的系列计算方法既扩展了计算焊接力学的基础理论和方法又具有较高的工程使用价值。