【作者】 朱茹敏；

【导师】 关绍康； 曹宏深；

【作者基本信息】 郑州大学 ， 材料加工工程， 2003， 硕士

【摘要】 板材皱曲是冲压成形时生产中常见的一种缺陷，也是导致冲压废品的重要原因，板材皱曲特性属于冲压成形性能范畴。方板对角拉伸试验即YBT模型是日本冲压行业著名学者吉田清太提出的评价板材冲压成形性能的著名试验。本文运用通用有限元软件Marc／Mentat对Al-Mg-Si基合金车身板材YBT模型进行数值模拟，分析研究Al-Mg-Si基合金车身板材在不均匀拉应力场作用下的皱曲动因，材料力学性能参数对其皱曲失稳特征值的影响，以及Al-Mg-Si基合金车身板材与不同冲压钢板皱曲行为的对比，并将数字化的虚拟仪表的概念引入到本文研究。 本文首先对板材成形有限元基本理论进行了阐述，并简略的介绍了大变形条件下的弹塑性本构方程。 对Marc／Hentat软件求解非线性问题的一些基本原理、求解方法、收敛判据及接触算法等进行简介与分析，在此基础上，构造出了方板对角拉伸有限元模型和提出了方板对角拉伸过程计算的边界条件的确定方法及模拟计算的参数设定。 运用Marc／Mentat软件分析研究了Al-Mg-Si基合金车身板材YBT模型拉伸过程中的位移场、应力应变场以及皱曲临界状态下的特征面上应力应变变化规律，揭示了Al-Mg-Si基合金车身板材的皱曲动因。由此得出：①YBT模型几何宽度不均匀所形成的横向角部区域，导致了主动型的纵向主轴拉应力和主轴伸长应变以及被动型的横向主轴压应力的不均匀传播与分布；②YBT模型上最容易发生皱曲的临界危险点是模型的中心；③YBT模型以及所有处在不均匀拉应力场作用之下的板料所发生的皱曲失稳，均具有弹性失稳、诱发性弹性失稳和塑性失稳三重性质；④整个模型的皱曲失稳决不仅仅只是与特征轴或特征截面上的不均匀应力应变相关，而是模型全场的应力应变不均匀传播和分布作用的结果。 基于YBT模型并借助于Marc软件的数值分析功能，通过假设板材各向同性以及不断变换弹性模量E、硬化系数K和屈服点σ_0.2的数值，揭示了Al-Mg-Si基合金车板材力学性能与YBT模型皱曲特征值之间的关系，得出提高Al-Mg-Si基合金车身板材的弹性模量、屈服点和硬化系数，对不同的皱曲失稳特征值具有不同的影响，但都会增大板料弹性皱曲失稳或诱发性弹性失稳的概率，因此仅从单因素角度考虑，为了保证Al-Mg-Si基合金车身板材的贴模性和定形性，弹性模量、屈服点和硬化系数均不要取值太高。 将YBT模型数值模拟视为虚拟板材冲压成形性能试验之一，以冲压成形性能和冲压成形工艺参数相业已比较明确的车身钢板为参照对象，在数字化空间采用对比方法研究Al-Mg-Si基合金车身板材皱曲特性之优劣。从载荷与应力出发，视摘要应变为结果对比分析Al一Mg一si基合金车身板材与低碳冲压钢板和高强冲压钢板的皱曲特性，得出:①板材屈服点过高会导致其YBT模型沿Y轴上下两端附近出现纵向伸长应变集中现象，这种应变集中首先会使模型中心主轴伸长应变值变得比较小，从而成为最容易皱曲失稳的危险点，这是高强冲压钢板较低碳冲压钢板和A1一Mg一Si基合金车身板材容易在不均匀拉应力作用下皱曲的重要原因之一;其次这种应变集中还会导致YBT模型的皱曲延伸率发生异常增大，从而丧失其作为板材皱曲特性评定指标的准确性;②不均匀拉应力场导致的横向压缩应变沿X特征主轴的不均匀分布，以及它们在整个模型X场中的不均匀分布，是板材在不均匀拉应力场作用下皱曲失稳的主要几何原因，皱曲失稳时的临界应变数值与板材材质结构及其材料屈服点大小相关，是估测和评定不同板材皱曲失稳性能的重要指标;③从皱曲的力学本质来看，A1一Mg一Si基合金车身板材的抗皱曲特性优于低碳冲压钢板和高强冲压钢板。则目前或今后欲进一步提高A1一Mg一Si基合金车身板材的抗皱曲特性，尚需在冶金方法允许的材料性能参数范围内，面向皱曲行为和皱曲特性值对它们进行科学与合理地优化选择及组合。如果综合考虑抗破裂性、贴模性和定形性三方面的综合指标，则对材料性能参数之间的选择与优化组合显得更为重要。 最后借用虚拟仪表的基本概念，并基于C++ Builder平台构造了板材皱曲特性的虚拟仪表，为今后研发虚拟板材冲压成形性能新技术建立了基础，同时也为利用前面的板材皱曲模拟分析工作逐渐搭建虚拟板材皱曲特性试验的框架和雏形。更多还原

【Abstract】 Sheet metal buckling characteristic belongs to the stamping formability. Sheet metal buckling is not only a familiar objection during the stamping process ,but also is the important cause of stamping waster .Yoshida Buckling Test(YBT)which has been developed by Japanese famous scholar Yoshida is a notable test for appraising the sheet stamping formability. The thesis mainly performs the FEM simulation of Al-Mg-Si based alloy auto body sheets using Marc/Mentat software, analyses and investigates buckling performance, buckling cause and buckling mechanism on new type Al-Mg-Si based alloy auto body sheets and the macro mechanical properties which effect the buckling characteristic in order to search the new scheme for optimizing properties of Al-Mg-Si based alloy auto body sheets and at the same time to provide the method foundation of the numerical simulation for investigating and innovating the virtual stamping formability test in the future .First, basic theory for the analysis of sheet metal forming is expounded, and constitutive equation for large elastoplastic deformation is introduced in this paper.Some basic problems of FEM, such as principles and algorithm for nonlinear problems, convergence criterion, contact algorithm and friction model, are analyzed and introduced in this paper. Moreover, the numerical model of YBT is created and the definition method of boundary condition and calculation parameters are put forward.The total fields of displacement, stress and strain in biaxial diagonal tension deformation process and the variation regularities of stress and strain are analyzed and investigated at critical buckling instability, and buckling causes on new type Al-Mg-Si based alloy auto body sheets are showed using Marc/Mentat software. The results found that: (1)the transverse corner field resulting from the uneven geometrical width of YBT model leads to the non-uniform spreads and distributions of the active lengthwise tensile stress, the stretchy strain and the passive transverse pressure stress in the principal axis; (2)the center of the YBT model is the most possible critical buckling instability point; (2)the buckling performance of the YBT model not only possess both properties of elasticity and plasticity, but also the interlaced distributions possible appear on the elastic and plastic stress points; (4)buckling instability of the total model not only is correlated with the non-uniform stress and strain on eigenaxis or eigensection, but also is the result of the total fields of stress and strain which spreadand distribute non-uniformly.Based on the YBT model and using Marc/Mentat software, the relationships of mechanical properties of Al-Mg-Si based alloy auto body sheets and buckling eigenvalues of the YBT model are searched by means of supposing sheet mental isotropy and changing modulus of elasticity, hardening coefficient and yield limit. The results show that: it is different effects to increase modulus of elasticity, hardening coefficient and yield limit for different buckling eigenvalues, but they will increase probability of elastic buckling instability or induced elastic instability. Therefore, only based on single factor, it couldn’t be too high to ensure fitability and fixability of Al-Mg-Si based alloy auto body sheets for modulus of elasticity, hardening coefficient and yield limit.Buckling characteristic of Al-Mg-Si based alloy auto body sheets is comparing with those of low carbon steel sheet and high intensity steel sheet using the YBT modle. The results show that: ﹊f the sheet mental has an excessively high yield limit, it will induce the lengthwise tensile strain focus in the ends of Y-axis. The focus reduces the tensile strain of the main-axis center, as yet the center easily becomes the dangerous point of buckling instability. It is why high intensity steel sheet appears easier buckling than low carbon steel sheet and Al-Mg-Si based alloy auto body sheets under the un-uniform tensile stress; ﹖he main causes of buckling instability are relative of the un更多还原