【作者】 刘毅；

【导师】 薛凤梅；

【作者基本信息】 太原理工大学 ， 材料与化工（专业学位）， 2023， 硕士

【摘要】 铝合金汽车轻量化是当前汽车工业的研究热点,其目的是通过采用轻量化的铝合金材料来减轻汽车的重量,提高汽车的燃油经济性和减少碳排放量。铝合金在汽车轻量化中的应用将会推动汽车工业的发展,为实现绿色、低碳、环保的社会发展目标做出重要贡献。损伤与断裂是铝合金板材成形过程中的主要缺陷,采用传统的损伤模型预测铝合金板材成形过程中的损伤断裂位置并不准确,深入研究损伤模型并进行合理的修正对铝合金板材成形破裂预测以及提高铝合金构件在汽车轻量化中的应用方面具有重要的工程价值。近年来,随着计算机领域的迅速发展,有限元数值计算方法（FEM）被广泛应用于金属材料塑性成形过程中,借助该方法,实现了复杂过程的仿真模拟,节省了大量成本与时间,有限元数值计算方法已经成为板料成形中最常用的模拟方法之一,可全面了解板料在成形过程中应力应变及损伤分布,对可能产生的成形缺陷及破裂位置做出准确的预测。本文以5052铝合金为研究对象,首先进行单向拉伸和拉伸加载卸载试验,结合数值模拟,得到Lemaitre损伤模型的损伤参数,并开发了基于Lemaitre损伤模型的VUMAT子程序,对模型进行修正,提出了一种更加精确的损伤值与塑性应变之间的非线性关系,探究了应变速率对材料的力学性能和损伤值的影响,并结合断口形貌分析了材料的断裂特性。结果表明:室温条件下,5052铝合金具有良好的塑性,在10^-3s^-1到10^-2s^-1应变速率下临界损伤值处于0.30到0.36之间,临界损伤值随着应变速率的增大逐渐增大;对比分析发现修正的Lemaitre损伤模型模拟得到的真应力-真应变数据与试验得到的数据之间相对误差更小;修正的Lemaitre模型数值模拟获得的试样断裂失效位置与试验之间的相对误差为3%,接近于试验结果;断口呈韧窝状分布,韧窝深且多,呈韧性断裂特征。针对5052铝合金进行杯突试验,结合数值模拟,进一步分析了修正的Lemaitre损伤模型的可靠性。通过对比试验与模拟的IE值、应力应变损伤分布以及宏观裂纹的相对位置对修正的Lemaitre损伤模型可靠性进行验证,同时利用SEM分析了不同加载速度下的杯突试验断口形貌,结果表明:铝合金板材杯突数值模拟过程中,板料的等效应力和等效塑性应变最大值出现在板料与凸模顶端接触的区域附近,呈圆环状分布,修正的Lemaitre损伤模型模拟得到的试样断裂断口呈弧形形状与试验断口形状接近;5mm/min和10mm/min加载速率下得到的5052铝合金杯突值分别为9.1 mm和9.5 mm,修正的Lemaitre损伤模型模拟预测得到的埃里克森杯突值与试验误差更小分别仅为4.38%和1.03%;5052铝合金的断口属于韧窝形断口,稠密的小韧窝中间分布着又大又深的韧窝,呈现出韧性断裂特点。对汽车发动机盖板成形过程进行数值模拟,将修正的Lemaitre损伤模型通过有限元分析软件结合VUMAT子程序模块进行二次开发套嵌,通过应力应变以及损伤预测发动机盖板成形的破裂位置,结果表明:发动机盖板在冲压成形过程中主要发生破裂的位置集中于凸模圆角与板料接触的位置及侧壁区域。更多还原

【Abstract】 Aluminium alloy vehicle lightweighting is a current research hotspot in the automotive industry,The aim is to reduce the weight of the vehicle,improve fuel economy and reduce carbon emissions by using lightweight Aluminium alloys,The application of Aluminium alloy in automotive lightweighting will promote the development of the automotive industry and make an important contribution to the achievement of green,low-carbon and environmentally friendly social development goals.Damage and fracture are the main defects in the forming process of Aluminium alloy sheets.The traditional damage model is not accurate in predicting the location of damage and fracture in the forming process of Aluminium alloy sheets,and an in-depth study of the damage model with reasonable modifications is of great engineering value in predicting the forming fracture of Aluminium alloy sheets and improving the application of Aluminium alloy components in automotive lightweighting.In recent years,with the rapid development of the computer field,the finite element method(FEM)is widely used in the plastic forming process of metal materials,with the assistance of this method,the simulation of complex processes is achieved,saving a lot of cost and time,the finite element numerical calculation method has become one of the most commonly used simulation methods in sheet forming,which can provide a comprehensive understanding of the stress-strain and damage distribution of the sheet during the forming process,and make accurate predictions on the possible forming defects and rupture locations.This paper is based on 5052 Aluminium alloy,firstly,the unidirectional tensile and tensile loading unloading tests are carried out and combined with numerical simulations to obtain the damage parameters of the Lemaitre damage model,and a VUMAT subroutine based on the Lemaitre damage model is developed to modify the model and propose a more accurate non-linear relationship between the damage value and plastic strain,and explore the the effect of strain rate on the mechanical properties and damage values of the material.The fracture characteristics of the material were also analysed in relation to the fracture morphology.The results show that 5052 Aluminium alloy has good plasticity at room temperature,and the critical damage value is between 0.30 and 0.36 at strain rates of 10-3s-1to 10-2s-1,and the critical damage value increases gradually with increasing strain rate;The relative error between the true stress-true strain data obtained from the modified Lemaitre damage model and the experimental data is smaller;the relative error between the fracture failure location of the specimen obtained from the numerical simulation of the modified Lemaitre model and the experimental data is 3%,which is closer to the experimental results;the fracture is distributed in the form of tough fractures,with deep and numerous tough fractures,which are characteristic of ductile fracture.The reliability of the modified Lemaitre damage model in the sheet forming process was further analysed by carrying out cupping tests for 5052 Aluminium alloy,combined with numerical simulations.The reliability of the modified Lemaitre damage model was verified by comparing the IE values,stress-strain damage distribution and the relative position of macroscopic cracks between the test and simulation,while the fracture morphology of the cupping test at different loading rates was analysed by SEM,The results show that during the numerical simulation of the cupping of Aluminium alloy plates,the maximum equivalent stress and equivalent plastic strain of the plates appear in the area of contact between the blank and the top of the die,with a circular distribution,and the fracture fracture of the specimens obtained from the modified Lemaitre damage model has a curved shape closer to the test fracture shape;The cupping values of 5052 Aluminium alloy obtained at loading rates of 5 mm/min and 10 mm/min were 9.1 mm and 9.5 mm,respectively,and the Erikson cupping values predicted by the modified Lemaitre damage model simulations were less than the experimental error of 4.38% and 1.03%,respectively;The fracture of 5052 Aluminium alloy belongs to the tough nest-shaped fracture,the dense small tough nest in the middle of the distribution of large and deep tough nest,showing excellent ductile fracture characteristics.The modified Lemaitre damage model was simulated numerically in combination with the VUMAT subroutine module of the finite element analysis software to predict the location of the rupture of the engine cover forming by stress-strain and damage.The results show that the main locations where rupture occurs during the stamping and forming process of the engine cover are concentrated in the contact area between the corner of the die and the sheet and in the side wall area.更多还原