【作者】 翟瑞雪；

【导师】 赵军； 钱志平；

【作者基本信息】 燕山大学 ， 材料加工工程， 2013， 博士

【摘要】 拉弯工艺是一种常见的金属型材弯曲成形方法。近几十年来，拉弯成形技术在理论解析分析、工艺参数制定和成形设备改进等方面得到了不断的完善；如今，这种技术因其制品精度高、产品表面质量好等优点被广泛应用于汽车、航空航天和建筑等领域。拉弯弹复规律的研究和弹复量的精确预测一直都是拉弯技术中的难题。实际生产和学术研究表明，拉弯的弹复与型材的截面形状、材料的力学性能和载荷的控制方式等因素相关。在过去的几十年里，国内外专家对型材拉弯弹复问题进行了大量的研究，得到了许多有价值的数据和值得借鉴的研究方法。然而，这些研究都是针具体的某种型材或单一的加载方式，对任意截面型材拉弯弹复的共性问题及不同加载方式对拉弯弹复的影响鲜有涉足，这便给实际生产中任意截面型材拉弯加载方式的选择和工艺参数的制定带来了障碍，极大地限制了拉弯工艺柔性制造特点的发挥。因此本文就任意截面型材在不同加载方式下的拉弯弹复问题开展了更为系统的深入的研究。本文在塑性弯曲工程理论的基本假设下，描述了任意截面型材在任意方式加载变形后的应变分布和弹复后的应变分布；将拉弯的弹复过程等效为反向弹性压弯过程，基于经典弹塑性理论和应变可叠加的原理，建立了统一的型材平面拉弯弹复方程，指明了拉弯弹复求解的一般性思路。在先拉伸后弯曲、先弯曲后拉伸和先拉伸后弯曲再补拉三种加载方式下，分别建立了型材平面拉弯的力学模型；详细地描述了拉弯加载过程中和加载后应力的分布状态，依据应力分布状态的不同，对拉弯的变形情况进行了详细地分类。基于双线性随动强化材料模型，给出了不同加载方式下及不同变形情况下截面应力应变的数学表达式；通过内力与外载荷的静力平衡关系推导出应变中性层曲率半径、弯矩、拉力和弯曲半径之间的数学关系；给出了所有变形情况的判定条件确立了型材平面拉弯弹复解析的通用方法。在不同的加载方式下，针对给定的矩形截面型材和U形截面型材进行了定量的弹复解析，获得了拉力、弯曲半径、加载方式对弹复的影响规律。基于转臂式拉弯机的工作原理，设计加工了一套液压控制的型材拉弯物理实验系统，针对给定的矩形截面型材和U形截面型材开展了拉弯弹复实验研究；利用有限元分析软件ABAQUS开展了有限元模拟分析，物理实验和有限元分析所获得的拉弯弹复规律与理论解析结果一致，数据吻合，从而佐证了理论解析结果和方法的正确性。本文针对任意截面型材在不同加载方式下拉弯的变形和弹复问题，系统地完成了力学模型的建立和弹复的力学解析，建立了型材平面拉弯的弹复解析理论体系；通过物理实验和有限元模拟手段对弹复解析理论进行了验证。研究表明：型材平面拉弯弹复理论适用于任意截面型材和任意加载方式，该理论的建立突破了单一截面型材在单一的加载方式下拉弯弹复研究的局限性，具有一定的学术价值；不同加载方式、不同拉力和不同弯曲半径下，型材拉弯的弹复量都是可以通过理论解析获得的，这对拉弯加载方式的选择和工艺参数的制定具有一定的工程指导意义，为型材拉弯柔性制造特点的进一步开发和应用提供了理论基础。更多还原

【Abstract】 Stretch-bending technique is a common method of metal profile bending processing.In recent decades, the theory, technology and equipments of stretch-bending have beencontinuously improved. Nowadays, stretch-bending technique is widely applied inautomotive, aerospace and building industry because of its advantages of high productsprecision and good surface quality.The research on stretch-bending springback law and accurate prediction ofspringback are always the key issues to be solved. The actual production and academicresearch indicates that, stretch-bending springback relates to the cross-section shape,material properties and loading control, etc. In the past few decades, many domestic andforeign experts have done great deal of research on profile stretch-bending and got a lot ofvaluable data and research methods which are worthy of reference. However, the pastresearch mainly focused on the profile with some given cross-section or some kind ofloading method. The common problem on stretch-bending springback of the profile withany cross-section and the influence of different loading methods on stretch-bendingspringback were rarely involved. In order to produce the advantages of stretch-bendingflexible manufacturing, it is necessary to do more in-depth research on stretch-bendingspringback of profile with any section.Under the basic hypotheses of plastic bending engineering theory, the straindistributions after loading and springback were described when taking no account of theshape of cross-section of profile or loading method. The process of stretch-bendingspringback was taken as process of reverse compress-bending. The springback equation ofplane stretch-bending was established based on the classical elastic-plastic theory and thecharacteristic of strain superposition.When the loading methods are pretension-bending, prebending-tension andpretension-bending-tension, different distribution states of stress and strain oncross-section after stretch-bending deformation were described in detail. Thestretch-bending deformation states were classified into different states. The mathematical expressions of tress and strain in different deformation states weregiven based on bilinear kinematic hardening material model. The mathematicalrelationships among stress neutral layer, strain neutral layer, moment, tension and bendingradius were derived through integrating of stress based on the relationship of staticequilibrium. The method of discriminating different deformation states was given.The universal analytic method and procedures of porfile plane stretch-bendingspringback were obtained. In different loading methods, the quantitative analysis wereexplored in this analytic method aiming at the profiles with U-section and rectangularsection. The springback law describes the influences brought by the tension, bendingradius and loading methods to springback.Based on the operational principle of double-sting stretch-bender, a set of hydrauliccontrol experimental system for profile plane stretch-bending was designed. Theexperimental research on stretch-bending of profile with U-section and rectangular sectionwas carried out. Based on the physical experiment, the finite element simulation analysiswas carried out using finite element analysis software ABAQUS. The springback lawsobtained by experiments and finite element analysis are agreed well with the analyticalresults.Aiming at the problem on stretch-bending and springback of profile with any sectionin different loading methods, this paper carried out systematical research on building ofmechanical models and mathematical analysis of springback. The theory of springbackanalysis for profile plane stretch-bending was established. The experimental andnumerical research was carried out to verify this thoery. The research indicates that, thetheory of springback analysis for profile plane stretch-bending is applicable to any profileand any loading method; the stretch-bending springback of profile with any cross-sectioncan be accurately predicted when loading method, bending radius and tension are alldifferent. This research breaks through the imitation of the research on the stretch-bendingof profile with single cross-section in a single loading method, enriches the theoreticalsystem of profile stretch-bending springback and provides a theoretical basis forstretch-bending flexible manufacturing.更多还原