【作者】 戴谋军；

【导师】 李落星； 樊友权；

【作者基本信息】 湖南大学 ， 材料工程， 2008， 硕士

【摘要】 首先介绍了铝及铝合金的基本性能、特点、分类及其应用;再对型材弯曲的主要方法及弯曲过程中产生的主要缺陷进行了概述;接着对有限元分析方法和软件ANSYS/LS-DYNA进行了介绍。通过实验得出了材料的条件应力——应变曲线,再计算得出了材料的真实应力——应变曲线,在建立材料力学性能本构时,对塑性变形阶段分别采用了直线和幂函数进行拟合,建立了两种本构方程,并进行了对比。然后用大型通用有限元软件ANSYS/LS-DYNA,对铝合金管材不同工况进行压弯模拟,并对有限元模拟中的几何模型、材料模型、单元特性、接触、约束、载荷的设定、回弹计算进行了描述。模拟得到了实验力——位移曲线、不同压弯量下的回弹角、截面畸变及残余应力,最后通过实验对模拟的压弯力、回弹、截面畸变三方面进行了验证。三方面的验证结果表明模拟比较真实的反映了实验情况,证明所建立的材料本构方程和有限元模型是有效的。四种工况中,实验力——位移曲线关系均成两个阶段,第一阶段均为直线,当型材扁平放置时,第二阶段实验力开始小幅上升,然后逐渐下降,但上升和下降的幅度均很小;当型材竖直放置时,第二阶段的实验力随着压头压下量的变大而逐渐变大。回弹角随着压头压下量的变化而变化,但变化的程度较小,基本可以忽略不计。但从变化的数值上来看,变化的趋势与压头半径有关。当压头半径为15mm时,回弹角随压头压下量的增加而略微变小:当压头半径为60mm时,回弹角随压头压下量的增加而略微变大。随着压头的不断下压,四种工况下型材的截面变形程度加剧。通过模拟的四种工况说明型材放置方式和压头半径大小影响着最大残余应力的大小和分布位置。更多还原

【Abstract】 Firstly the performances, characteristics, classifications and applications of aluminum and aluminum alloy are introduced in this paper, then the primary bending processes and main defects of bending process are summarized also. Then the finite element methods, finite element technology and the software ANSYS / LS-DYNA were introduced.The condition stress strain curve of the material properties were concluded by experiments, then the real stress strain curve of the material properties was calculated and plotted. When the material constitutive equation was established, the linear fitting method and the power function fitting method were used to fit the stage of plastic deformation, and then two material constitutive equations are concluded and compared.Then the finite element analysis software ANSYS/LS-DYNA is used to simulate press bending process of different operating condition of aluminum alloy profiles. And some simulation conditions are described, such as the geometric model, the material model, the unit properties, the contacts, the constraints, the load settings, springback calculation of finite element simulation, and so on. The finite element simulation concluded the bending force-displacement curves, the springback angle of different bending displacement, the cross section distortion of different bending displacement and the residual stress of different bending displacement. At last, the three aspect simulation results, such as the bending force, the springback angle and the cross section distortion were verified by experiments. The three aspect experiments’ results show that the simulation conclusions are consistent with experiments; it testified that the material constitutive equation, finite element model and finite element parameters are correct and effective.The bending force-displacement curves of the four operating conditions of the experiment are composed of two stages. The first stage, the curves are all straight, when the aluminum profiles were placed at flat location direction, firstly the bending force of the second stage gradually rose and then gradually decline, but the rate of rise and decline were very small; when the profile were placed at thickness location direction, the bending force of the second stage gradually rose with the displacement increase. The springback angle varies with the displacement increasing of bending head, but the extent of vary is very small, which can be ignored. The changes’ results show that the trend of change is related with the radius of the bending head’s radius. When the radius of bending head is 15 mm, the springback angle gradually decline with the displacement increasing of bending head. When the radius of the bending head is 60 mm, the springback angle gradually rose with the displacement increasing of bending head. In the four different operating conditions, the cross section distortion gradually rose with the displacement increasing of bending head. The four operating condition simulation results shows that the numerical and location of the maximal residual stress are related with the bending location and the radius of the bending head.更多还原