【作者】 曾国；

【导师】 来新民； 李淑慧；

【作者基本信息】 上海交通大学 ， 车辆工程， 2009， 博士

【摘要】 冷弯型钢具有断面均匀、生产率高、能源消耗低等优点,在汽车、建筑和桥梁等行业具有广泛的应用前景。由于冷弯型钢往往作为结构的主要承载部件,其残余应力是决定结构安全系数和服役性能的关键要素。而冷弯型钢的辊弯成形工艺是一个反复加载、卸载的过程,各成形道次变形相互耦合,变形区不断变化,特别是闭口冷弯型钢制造还涉及到热力耦合的焊接过程,影响成形质量的工艺参数众多,残余应力的分析与控制十分困难。由于理论上缺乏系统的仿真分析和预测方法,工程上缺少成熟的残余应力行业标准和规范,限制了我国冷弯型钢在大型工程上的应用。本文以多道次辊弯成形冷弯型钢为研究对象,采用数值仿真和实验分析相结合的手段对多道次辊弯成形工艺产生的残余应力进行了深入的研究。在分析多道次辊弯成形工艺和焊接过程的基础上,以大型工程有限元分析软件ABAQUS为平台,基于隐式算法,建立了面向残余应力预测的开口与闭口冷弯型钢多道次辊弯成形及焊接仿真分析模型,对生产工艺各个因素对冷弯型钢最终残余应力分布的影响规律展开了研究。具体开展了以下几个方面的研究工作:(1)面向残余应力预测的多道次辊弯成形仿真方法研究+-以已有文献的实验模型为对象,基于隐式算法,建立了面向残余应力预测的多道次辊弯成形仿真方法,解决了仿真过程的收敛问题,并对影响冷弯型钢成形预测精度的仿真参数进行了分析。同时,以开口冷弯型钢仿真方法为基础,通过接触面法向不分离和多节点方程约束等技术实现合口过程模拟,提出了基于成形与合口两步仿真的闭口冷弯型钢仿真方法,并以实际的闭口产品验证了闭口冷弯型钢仿真模型。已取得研究成果对多个行业关键产品以及辊弯成形工艺相关的仿真研究具有参考价值。(2)开口冷弯型钢辊弯成形残余应力的实验与仿真分析对X射线衍射方法进行了理论分析,推导了内表面残余应力测量的基本公式,讨论了残余应力的测量方法,完成开口冷弯型钢残余应力的测试。基于前面仿真方法的研究成果和实际产品设计参数,建立并验证了辊弯成形开口冷弯型钢残余应力的仿真模型,对辊弯成形产生的残余应力进行了分析讨论。最后,基于所建立的模型,研究了材料参数、工艺参数和形状参数对开口冷弯型钢内外表面残余应力分布的影响规律。揭示的开口冷弯型钢残余应力变化规律可以为辊弯成形工艺设计人员提供有益的参考。(3)闭口冷弯型钢焊接过程完全热力耦合分析在闭口冷弯型钢仿真方法的基础上,提出了采用单元生热方式加载热源的热力耦合分析方法。在确定仿真焊接热源和焊接热损主要形式的基础上,着重分析了完全热力耦合分析的单元类型、网格划分和材料的热物理性能和相关仿真参数。以已经进行了残余应力测量的闭口冷弯型钢设计参数为依据,建立并验证了产品的焊接完全热力耦合分析仿真模型。研究得到的完全热力耦合分析方法可用于类似的焊管和其他闭口截面焊接过程的成形预测或深入分析。(4)辊弯成形闭口冷弯型钢残余应力实验研究应用X射线衍射方法对闭口冷弯型钢产品进行了大量的残余应力实验研究,得到包括两种材料、两种工艺(圆变方、方变方)、13个不同规格试件、共560点次的残余应力测量结果。在分析大量试件内外表面及沿厚度方向残余应力实验数据的基础上,研究了影响闭口冷弯型钢残余应力分布的几个重要因素,结果表明径厚比对残余应力的影响较大。本文的实验研究为制定残余应力行业标准和规范提供了数据支持。本文在充分吸收和借鉴前人研究成果的基础上,对多道次辊弯成形冷弯型钢残余应力进行了深入的研究和探讨。研究以数值模拟为主,辅以大量的实验研究,为多道次辊弯成形冷弯型钢残余应力预测提供了有效的方法,从更深层次上揭示了辊弯成形残余应力形成过程的影响规律。本文的研究成果可推动辊弯成形冷弯型钢在大型工程中的应用,为进一步制定冷弯型钢残余应力行业规范和标准提供数据支持,同时能推广应用于多个行业关键产品的辊弯成形工艺设计过程中,具有重要的理论研究价值和工程实践意义。更多还原

【Abstract】 As an economic profile product, roll-forming product is widely used in transportation, engineering machine, civil construction because of its uniform section, high strength and low consumption of production energy. With more and more application of high-strength steel, residual stresses (RS) is a key element of safety factor and performance of cold-formed sections when it is used as main part in major engineering works. Roll-forming process is very complicated. It is a process of large displacement and finite strain, in which the friction between the strip and rolls is included. Because roll-forming is a process with geometric, material and boundary nonlinearity, its forming rules is hard to control, which in turn make it difficult to study RS of the sections. Because there is no systemic simulation analysis and prediction technique in theory and no RS trade rules and standards in the industry, the application and development of cold-formed sections in major engineering works is delayedIn this paper roll-forming sections with multi-stand were taken as object, and RS produced from the process was studied in detail with finite element method (FEM) simulation and experiment. Based on the analysis on the process of roll-forming and welding, used commercial FEM code ABAQUS to establish the FEM simulation model from witch RS of open and closed sections produced by roll-forming can be predicted. On the ground of a large number of experimental data of RS, the effect of process factors to distribution of RS is studied. Based on above research objectives, the following four works were done mainly:(1) FEM simulation model of roll-forming process for residual stresses predictionThe method of computing algorithm and contact algorithm was analyzed. Taking a real product produced by factory as objective, the method of establishing simulation model was studied. The simulation manner, material model, element type and mesh, simulation algorithm, load and boundary were discussed in detail, especially for the solution of convergence. The reliability of the simulation model is check by the experimental data. Then the analysis of parameters for precision of the model was conducted. At the same time, based on the model for the open sections, the simulation model for closed section was present using continuum shell element in which two steps were introduced, forming and closing. Emphasis was put on the load and boundary condition definition. Taking a real closed-form section product, the FEM simulation for multi-stand roll-forming process was conducted successfully, and the simulation results were proved by the measurement.(2) Experiment and simulation analysis for roll-forming process of open sectionsThe method of X-rays diffraction was studied and the basic formula for inside surface measurement was derived. Based on X-rays diffraction method, inside surface and outside surface longitudinal residual stresses (LRS) and transversal residual stresses (TRS) of a real open section product were measured. Using the models researched above and parameters of product, the RS FEM simulation model for multi-stand roll-forming of this real open section product was established. Through the comparison of dimension measurement and RS experimental data, the reliability of the FEM simulation model based on implicit algorithm studied above was validated. Finally, on the ground of FEM model, the research on the effect of material, process and dimension factors to RS of open sections was conducted in detail.(3) Fully coupled thermal-stress analysis for closed-form sections of roll-formingBased on the research on simulation model for closed-form section, a method of fully coupled thermal-stress analysis using element body hot generated was present. Firstly, the method of simulation algorithm for welding is introduced, and the heat source and heat waste of the simulation were made sure. Then the element type, mesh, heat physics parameters of material and simulation was analyzed in detail. On the ground of the design data of a real product of which RS have been measured, the fully coupled thermal-stress analysis simulation model for multi-stand roll-forming was established. Through the comparison between the experiment and simulation, the reliability of the fully coupled thermal-stress analysis simulation model was validated. The model present an acceptable solution for further research for high-frequency induced welding process. (4) Residual stresses experiment for roll-formed closed-formed sectionsIn the paper a large amount of measurement were conducted for the close-formed sections using X-rays diffraction method. There were totally 13 different specimens, including 2 materials and 2 processes, and 560 points to be measured. All specimens’outside surface RS were measured. Considering the limitation of the equipment’s dimension, only inside surface RS of 2 large dimension specimens were measured. At the same time, since through thickness residual stresses is also import for the application of the product, in the experiment machining was used for rough removal and electrolytic polishing was followed. Based on a large number of experimental data, several important factors affecting the distribution of RS, and results showed that the slenderness (b/t) values have an important effect on the distribution of RS.In this study, by absorbing and referring the exist achievements, RS of roll-formed sections were researched and analyzed. Based on the FEM simulation and a large number of experiments, the rule of RS in multi-stand roll-forming is present. The objective of the research is to facilitate the application of roll-formed sections in major engineering works, and to provide the data support for establishment of RS trade rules and standards in the industry. Above all, the research fruits in this dissertation have very important theory value and practice significance.更多还原