【作者】 伍杰；

【导师】 周益春；

【作者基本信息】 湘潭大学 ， 材料科学与工程， 2012， 博士

【摘要】 镀层金属薄板是指在金属薄板基底上镀覆上一层具有耐腐蚀、耐磨损、高强度等特殊功能金属层的一种复合材料。由于这些优良的功能，镀层金属薄板在建筑行业、机械设备、航空航天、仪器仪表以及车辆制造等行业发挥着重要的作用。然而，很多镀层金属薄板材料在应用之前都要经历冲压成形，这一过程包含几何非线性(大位移和大变形等)、材料非线性(弹塑性变形等)以及边界非线性(接触和摩擦引起)等多重非线性问题，导致在冲压成形过程中出现起皱、断裂和镀层剥落等失效现象。这些非线性问题造成镀层金属薄板冲压成形过程的变形机理复杂化，失效的模式多样化，使得传统的依赖单一成形极限图的方法不能够对其失效行为进行宏观、具体的描述，必须另辟蹊径，探究解决这一问题的有效方法。本文从理论分析、有限元数值模拟和实验三个方面来研究镀层金属薄板在冲压成形中的失效行为，力图最终建立镀层金属薄板冲压成形过程中的失效机制图，取得的主要创新性研究结果如下：(1)将量纲分析的方法引入到镀层金属薄板冲压成形的失效分析中，应用量纲分析的基本原理——Π定理，建立了冲压成形中失效时的最大冲头位移与工艺参数(包括压边力，板材料与冲压模具之间的摩擦系数等)、模具几何参数(包括冲头与凹模的圆角半径以及冲头与凹模之间的间隙)和板材力学性能参数之间关系的理论框架；并研究了镀层金属薄板冲压成形中最大冲压力与板材力学性能之间的关系，通过理论分析的方法验证了量纲分析的正确性，为采用量纲分析法建立镀层金属薄板冲压成形的失效机制图奠定理论基础。(2)将镀层金属薄板冲压成形中的失效问题简化为其在简单的应力状态下的塑性失稳问题。采用复合材料的基本理论，将镀层金属薄板冲压成形中常见的失效现象，冲头圆角处的断裂，简化为复合板材料在单轴拉伸载荷作用下的失稳问题，利用分散颈缩失稳理论，得到了镀层金属薄板在拉伸失稳(断裂)时的临界应力和应变值与其组分材料失稳参数之间的关系。将镀层金属薄板冲压成形中珐琅部分的起皱现象，简化为环形板在径向拉伸，环向压缩作用下的拉压失稳问题进行了研究，基于能量分析的方法，得出了无压边力与有压边力这两种情况下的起皱产生的准则。(3)基于连续介质损伤力学结合有限元数值模拟，研究了镀层金属薄板冲压成形中的失效行为。确定了有限元方法模拟冲压成形问题的定解条件，并基于连续介质的损伤力学材料模型，建立了镀层金属薄板冲压过程的ABAQUS有限元模型。结果表明，镀层金属薄板冲压成形中主要存在两种失效模式，即起皱和断裂。在此基础上，结合量纲分析建立的冲压成形中失效时的最大冲头位移与工艺参数(包括压边力，板材料与冲压模具之间的摩擦系数等)、模具几何参数(包括冲头与凹模的圆角半径以及冲头与凹模之间的间隙)和板材力学性能参数之间关系的理论框架，提出了一种建立镀层金属薄板冲压成形中失效机制图的方法，并以镍镀层金属薄板为研究对象，建立了基于工艺参数和几何参数的失效机制图。(4)以镍镀层金属薄板为研究对象，对镀层金属薄板冲压成形中的失效问题进行了实验研究。根据自行设计的冲压成形模具，结合万能拉伸机对镍镀层金属薄板进行了冲压成形的实验研究，采用高精度Argus网格应变测试系统对成形件中的应变分布进行了测定。镍镀层金属薄板的冲压成形中，产生了两种失效模式，即珐琅部分的起皱和冲头圆角处的断裂。通过对比冲压过程中实验与数值模拟结果的冲力冲程曲线、成形件的形状和应变分布等，证明了有限元预测的准确性，并进一步从实验上验证了镀层金属薄板冲压成形中失效机制图的有效性。总之，本论文主要对镀层金属薄板在冲压成形中的失效问题进行了理论分析，包括采用量纲分析的方法对冲压成形中的最大载荷以及失效前的最大冲压深度进行了分析；采用复合板理论对镀层金属薄板在拉伸和拉压状态下的塑性失稳问题进行了理论推导；基于连续介质损伤力学的材料模型并结合有限元数值模拟，根据量纲分析的理论模型，建立了镀层金属薄板冲压成形中基于工艺参数和几何参数的失效机制图。最后，以镍镀层金属薄板为研究对象，研究了镀层金属薄板冲压成形实验中的失效行为，验证了有限元数值模拟的正确性和基于量纲分析结合有限元模拟建立镀层金属板冲压成形中失效机制图的可行性与有效性。更多还原

【Abstract】 Coated metal sheet is a kind of composite materials, which a metal layer withresistant to corrosion and wear, high strength, and other special functions is depositedon metal substrates. Due to these excellent properties, it plays a very important role inbuilding industry, mechanical equipment, aeronautics and astronautics, instrument andvehicle manufacturing industry. However, in the process of deep drawing of coatedmetal sheet, it contains many multi-nonlinearity problems, such as geometricalnonlinearity (large displacement and large deformation), material nonlinearity(elastic-plastic deformation) and nonlinear boundary (contact and friction), whichresults in many kinds of failure modes such as wrinkling, fracture and spalling of thecoating. Nonlinear problems cause the complexion of deformation principles duringdeep drawing of coated metal sheet, and the variety of the failure modes. So thetraditional onefold Forming Limit Diagram(FLD) method can’t study the failuremacroscopically and comprehensively. It is necessary to develop other methods tosolve the problem. In the thesis, the failure problems of the coated metal sheet in thedeep drawing process were studied by theoretical analysis, finite element modelingand experiments, respectively. And the achieved main contents and results are asfollows:(1) The dimensional analysis was introduced into failure analysis of coated metalsheet in the deep drawing. When the failure happened in the process of deep drawing,the frame relation between the maximum punch displacement and process parameters,geometry parameters, and material parameters was established according to the Пtheorem of the dimensional analysis. The relationship between the maximum punchload and the mechanical properties of the coated metal sheets was also analyzed bythe П theorem of the dimensional analysis. And the relationship was verified by thetheoretical analysis, which provide theoretical guidance for establishing the failuremechanism map.(2) The failure of coated metal sheet in the deep drawing was converted into theplastic instability of coated metal sheet under simple stress state. The fracturephenomenon in the corner radius of punch was considered as the plastic instabilityunder the uniaxial tension. The relationship between the critical fracturing stress andstrain point of coated metal sheet and those of the component’s was obtained based onthe basic theory of composite sheet. The wrinkle problems of the flange part during deep drawing coated metal sheet was also studied according to the basic theory ofcomposite sheet and energy, the rules when wrinkles start emerging were formed withand without consideration the blank holder force.(3) The finite element modeling of failure behavior of the coated metal sheet inthe deep drawing process was built based on the continuum damage mechanics modelin Chapter3. The definite conditions for the simulation of the deep drawing withfinite element modeling were ensured. According to the finite element, there are maintwo failure modes in the deep drawing of coated metal sheet, i.e. fracture andwrinkling. A method of establishing failure mechanism map was suggested based onthe dimensional analysis and finite element modeling. The nickel coated metal sheetbeen treated as the research object, the failure mechanism map was built based onboth the process parameters and the geometry parameters.(4) Deep drawing experiments was made on the nickel coated metal sheet withself-designed drawing tools and the universal drawing machine. Two kinds of failuremodes occurred in the deep drawing process. These were the wrinkle of the flangepart and the fracture at the punch fillet. The experimental results were consistent withthe results of the finite element modeling by comparing the punch load displacementcurve, the shape of drawn parts and the distribution of strain, which demonstrated theaccuracy of the finite element modeling, and verified the effectiveness of failuremechanism map in the deep drawing process of the coated metal sheet via combinedthe finite element modeling with dimensional analysis.In general, the failure problem during deep drawing the coated metal sheet wasanalyzed theoretically in the thesis. The detailed contents were as following: themaximum load in the deep drawing process and the maximum drawing depth beforefailure were discussed via dimensional analysis; theoretical derivation on the fractureand wrinkle problems were carried according to the composite sheet theory; thefailure modes were predicted via the finite element modeling, and demonstrated theaccuracy of the finite element modeling by deep drawing experiment; the failuremechanism map was built based on the process parameters and geometry parametersin the deep drawing process of the coated metal sheet.更多还原