基于Yoshida-Uemori材料模型的汽车结构件冲压回弹分析

Yoshida-Uemori随动硬化材料模型能够准确描述应变路径发生变化时材料性能的改变,从而较好地反映复杂加载情况下材料的各向异性.本文基于JSTAMP件分别采用Yoshida-Uemori随动硬化材料模型和各向同性硬化材料模型对汽车高强钢结构件的冲压成形进行了仿真分析与回弹预测,研究了不同材料硬化模型对回弹预测精度...     

复合材料旋转壳稳定性有限元分析和横向剪切变形的影响分析

对复合材料旋转壳的失稳问题进行了有限元推导, 建立了考虑横向剪切变形的旋转壳稳定性分析模型。在应变向量阵中引入了横向剪切应变, 从而考虑了剪切的影响。为了避免剪切自锁, 刚度的计算采用一点高斯积分法, 几何刚度的推导采用Stricklin 法。最终将稳定性问题归结为特征值问题。数值算例表明, 对于各向同性和复合材料旋转壳, 横向剪切变形均使其临界载荷降低。在稳定性分析中, 横向剪切变形对各向同性材料旋转壳的影响较小, 对复合材料的影响较大。      

多点复合渐进成形与单点渐进成形的对比分析

为提高金属板材渐进成形的成形质量、成形精度、成形效率和成形极限,了解不同渐进成形工艺对制件成形性能的影响,本文以典型方锥台制件为研究对象,利用有限元软件MSC.Marc对2种渐进成形工艺进行了三维建模,对比分析了单点渐进成形和多点复合渐进成形对制件等效塑性应变、厚度分布和成形精度的影响.数值模拟结果表明:单点渐进成形的等效塑性应变和厚度减薄主要集中在制件相邻侧壁间的拐角处,而多点复合渐进成形的等效塑性应变和厚度减薄均匀地分布在制件成形区;相同成形工艺参数下,相比单点渐进成形,多点复合渐进成形更有利于制件的成形效率、成形质量、成形精度和成形极限的提高,更有利于抑制破裂等失稳现象的产生.2种渐进成形工艺的成形试验表明,数值模拟结果与试验相符.     

基于M−K理论的NbTiAl合金高温成形极限曲线预测

目的 NbTiAl合金在常温下的塑性较差,针对300 ℃时NbTiAl合金的成形性能进行研究,探究其在高温环境下的力学性能和成形极限,分析理论预测成形极限的可行性,为进一步研究铌合金性能和扩展其工程应用提供理论参考。方法 采用高温单拉和高温成形极限试验,获得了NbTiAl板材在300 ℃的应力应变曲线及成形极限曲线,使用Swift硬化模型针对塑性变形段进行拟合,并采用M−K失稳理论,结合相应的材料本构模型,对NbTiAl合金在高温环境下的成形极限进行了理论预测,并与实验数据进行了对比。结果 NbTiAl合金在300 ℃时的塑性应变阶段仍然具有加工硬化效应,在初始厚度不均度f0为0.998时,得到的理论曲线与试验点在左侧拉−压区符合得较好,但对右侧拉−拉区的理论预测与试验结果相差较大。结论 NbTiAl合金在300 ℃时具有较好的成形性,采用合适的不均匀度系数,利用M−K理论可以较好地预测NbTiAl合金高温成形极限曲线左侧拉−压区的极限应变,但对右侧拉−拉区域极限应变的预测结果误差较大。     

铝合金板材抗凹性能研究

通过力学性能测试、烘烤硬化性能测试和抗凹性能测试,研究了用于制备汽车覆盖件的6016铝合金板材的抗凹性能以及抗凹性与材料力学性能和烘烤硬化性能之间的关系。结果表明:6016铝合金板材经两年自然时效后,其强度略有增加,加工硬化指数n值和延伸率增大;板材在不同温度条件下经30 min烘烤后强度增加,烘烤硬化值随着温度升高而显著增加,表现出良好的烘烤硬化性能;板材的抗凹性能与烘烤工艺有关,烘烤温度越高,烘烤后材料的屈服强度越高,板材的抗凹性能越好。     

碳纤维织物力学性能和冲压成形实验研究

在实际成形过程中,碳纤维复合材料往往处于复杂的应力状态,开展近于真实载荷环境下的力学试验分析,能够更准确地认识实际应用中材料的成形性能和变形机理.为获得碳纤维织物的基本力学特性,设计了平纹碳纤维织物拉伸试样及成形试样,进行了单轴拉伸、双轴拉伸、镜框剪切试验和方盒冲压成形实验研究,对比了不同双拉比及纱线取向对力学性能及成形性能的影响.研究结果表明:碳纤维织物具有高度的非线性、各向异性和双拉耦合特性,即经纬向纤维的力学性能会相互影响;剪切变形是成形过程中的主要变形模式,当剪切角达到临界锁死角时,织物发生起皱现象;同种织物不同纱线取向试样表现出不同的成形性能,因此可以根据零件几何形状选择合适纤维取向的织物,从而减少缺陷,优化成形零件的力学性能.研究结果为后续建立碳纤维织物本构模型和成形仿真奠定了基础.     

“塑性应变比(r值)和减薄率(η值)试验方法”专题报道征稿通知——《理化检验-物理分册》2021年专题报道三

一、专题简介塑性应变比(r值)与材料的成形性能有着密切的关系,作为评价金属板材成形性能优劣、揭示因织构所主导的各向异性度强弱的重要指标,在金属板带和管材产品研发、生产质量控制与工业选材等方面得到了广泛应用,其反映了金属材料抵抗厚度减薄的能力。这个参数目前是采用单轴拉伸试验,测试试样宽度方向真实塑性应变和厚度方向真实塑性应变,计算宽厚比得到的。     

“塑性应变比(r值)和减薄率(η值)试验方法”专题报道征稿通知——《理化检验-物理分册》2021年专题报道三

一、专题简介塑性应变比(r值)与材料的成形性能有着密切的关系,作为评价金属板材成形性能优劣、揭示因织构所主导的各向异性度强弱的重要指标,在金属板带和管材产品研发、生产质量控制与工业选材等方面得到了广泛应用,其反映了金属材料抵抗厚度减薄的能力。这个参数目前是采用单轴拉伸试验,测试试样宽度方向真实塑性应变和厚度方向真实塑性应变,计算宽厚比得到的。     

模具结构对箔板电磁微成形的影响

对T2紫铜箔板进行电磁微成形实验,研究不同模具结构对材料成形性能的影响.采用激光共聚焦显微镜及轮廓仪研究不同模具结构对箔板电磁微成形的影响规律,分析模具结构对材料流动规律的影响.研究结果表明:随着电压的升高坯料出现不同程度的翘曲现象,采用凸型模具更有利于凹模内气体的排除,使得坯料能够迅速贴模;随着电压的升高材料成形性不断提高,采用凹型模具比采用凸型模具更加有利于微槽精度的提高;电磁成形制件应变分布均匀,凸型模具成形制件壁厚最小值出现在微槽侧壁,成形过程以拉深成形为主;凹型模具成形制件最小壁厚出现在微槽底部,成形过程以胀形为主.     

“塑性应变比（r值）和减薄率（η值）试验方法”专题报道征稿通知——《理化检验-物理分册》2021年专题报道三

正一、专题简介塑性应变比(r值)与材料的成形性能有着密切的关系,作为评价金属板材成形性能优劣、揭示因织构所主导的各向异性度强弱的重要指标,在金属板带和管材产品研发、生产质量控制与工业选材等方面得到了广泛应用,其反映了金属材料抵抗厚度减薄的能力。这个参数目前是采用单轴拉伸试验,测试试样宽度方向真实塑性应变和厚度方向真实塑性应变,计算宽厚比得到的。     

Numerical analysis of panels’ dent resistance considering the Bauschinger effect

The Bauschinger effect should be considered in the analysis of panels’ dent resistance, because sheet metal experiences a complex loading history from stamping to denting. This paper studies the modeling and simulation of panels’ static dent resistance, taking the Bauschinger effect into consideration. Our work covers two parts: simulation and experiment. Procedures of drawing, springback I, indenting and springback II are simulated in a multiple step analysis. Different hardening models, including the isotropic hardening model, the linear kinematic hardening model and the nonlinear combined hardening model are used, respectively, in simulation. Comparing the simulation results with the experiment results, we find that the Bauschinger effect has a great influence on panels’ dent resistance. When panels are made of high strength steel or stamped with a high Blank Holder Force (BHF), the Bauschinger effect on panels’ dent resistance is more severe. Considering the effect in numerical analysis would improve the simulation accuracy effectively. The work of this paper is beneficial to material selection and processing optimization for automobile exterior panels.     

Finite element implementation of non‐linear elastoplastic constitutive laws using local and global explicit algorithms with automatic error control

Implicit stress integration algorithms have been demonstrated to provide a robust formulation for finite element analyses in computational mechanics, but are difficult and impractical to apply to increasingly complex non‐linear constitutive laws. This paper discusses the performance of fully explicit local and global algorithms with automatic error control used to integrate general non‐linear constitutive laws into a non‐linear finite element computer code. The local explicit stress integration procedure falls under the category of return mapping algorithm with standard operator split and does not require the determination of initial yield or the use of any form of stress adjustment to prevent drift from the yield surface. The global equations are solved using an explicit load stepping with automatic error control algorithm in which the convergence criterion is used to compute automatically the coarse load increment size. The proposed numerical procedure is illustrated here through the implementation of a set of elastoplastic constitutive relations including isotropic and kinematic hardening as well as small strain hysteretic non‐linearity. A series of numerical simulations confirm the robustness, accuracy and efficiency of the algorithms at the local and global level. Published in 2001 by John Wiley & Sons, Ltd.     

Characterization of stress–strain behavior of a cast TRIP steel under different biaxial planar load ratios

This paper investigates the stress–strain curves of different load paths and the initial yield surface of a metastable austenitic stainless cast steel under biaxial planar loading using cruciform specimens. These tests were carried out on a 250 kN biaxial servohydraulic tension-compression testing machine. The laborious stress determination was undertaken with a new testing method by using global elastic unloading to measure the local stiffness. Isotropic yielding and mainly isotropic strain hardening were found. To evaluate the microstructure, the martensite formation was detected by use of a ferrite sensor and scanning electron microscopy and electron backscatter diffraction were applied.     

Plastic buckling of moderately thick hemispherical shells subjected to concentrated load on top

This study presents the analytical, numerical, and experimental results of moderately thick hemispherical metal shells into the plastic buckling range illustrating the importance of geometry changes on the buckling load. The hemispherical shell is rigidly supported around the base circumference against horizontal translation and the load is vertically applied by a rigid cylindrical boss at the apex. Kinematics stages of initial buckling and subsequent propagation of plastic deformation for rigid-perfectly plastic shells are formulated on the basis of Drucker–Shield’s limited interaction yield condition. The effect of the radius of the boss, used to apply the loading, on the initial and subsequent collapse load is studied. In the numerical model, the material is assumed to be isotropic and linear elastic perfectly plastic without strain hardening obeying the Tresca or Von Mises yield criterion. Both axisymmmetric and 3D models are implemented in the numerical work to verify the absence of non-symmetric deformation modes in the case of moderately thick shells. In the end, the results of the analytical solution are compared and verified with the numerical results using ABAQUS software and experimental findings. Good agreement is observed between the load–deflection curves obtained using three different approaches.     

Biaxial buckling analysis of double-orthotropic microplate-systems including in-plane magnetic field based on strain gradient theory

Background/purposeThis paper deals with analysis of biaxial buckling behavior of double-orthotropic microplate system including in-plane magnetic field, using strain gradient theory.MethodsTwo Kirchhoff microplates are coupled by an internal elastic medium and also are limited to the external Pasternak elastic foundation. Utilizing the principle of total potential energy, the equilibrium equations of motion for three cases (out-of-phase buckling, in-phase buckling and buckling with a plate) are acquired. In this study, we assumed boundary conditions of all the edges are simply supported. In order to get exact solution for buckling load of system, Navier approach which satisfies the simply supported boundary conditions is applied.ResultsVariations of the buckling load of double-microplate system subjected to biaxial compression corresponding to various values of the thickness, length scale parameter, magnetic field, stiffness of internal and external elastic medium, aspect ratio, shear stiffness of the Pasternak foundation and biaxial compression ratio are investigated. Furthermore, influence of higher modes on buckling load is shown. By comparing the numerical results, it is found that dimensionless buckling load ratio for in-phase mode is more than those of out of phase and one microplate fixed. Also it is shown that the value of buckling load ratio reduces, when non-dimensional length scale parameter increases.ConclusionHowever, we found when properties of plate are orthotropic the buckling load ratio is more than isotropic state. Also, by considering the effect of magnetic field, non-dimensional buckling load ratio reduces.     

镁合金板材等通道弯曲变形模拟与实验

目的通过设计一种等通道弯曲变形工艺,实现镁合金板材沿厚度方向较均匀的剪切应变。方法利用ABAQUS数值模拟并结合应变非均匀性评估方法,系统研究不同厚度镁合金板材在相同变形参数下剪切应变分布特征,比较实验结果说明模型准确性。结果等通道弯曲变形可以在不同厚度板材中实现较为均匀的剪切应变,且随着板材厚度的增加而提高。关于成形力的模拟和实验结果吻合良好,表明数值模拟方法能够较好实现ECAB变形过程的预测。结论由于该工艺能够引入均匀剪切应变,有望在镁合金板材组织和织构优化方面取得研究与应用价值。     

Influence of material properties and stamping conditions on the stiffness and static dent resistance of automotive panels

The use of thinner sheets and the introduction of new materials has meant that the stiffness and dent resistance of exterior panels has become more focused in the automotive industry during the last years. The objective of this study was to investigate the influence of material choice and the effect of varying stamping process conditions on the stiffness and static dent resistance of automotive panels. The experiments were performed on a double-curved panel. Four different materials were included in the study: an aluminium grade, a mild steel, a high-strength steel and a stainless steel. For each material, two different stamping-process conditions were adopted to obtain different strain, stress and thinning distributions in the panels. The same stamping process conditions were applied to all four materials. It can be concluded that the material grade significantly influences the static dent properties. The high-strength steel showed considerably better dent resistance than the other materials. The aluminium panels had slightly better dent resistance than the mild steel panels, although having much lower stiffness. The stainless steel grade had the lowest dent resistance, despite its high yield stress. An effect of the stamping process conditions was also found. Increased blankholding, with consequent increased strain levels in the panels, was generally beneficial to the static dent resistance. The experiments show very little scatter, indicating that the testing methodology developed worked satisfactorily.     

Einfluss elastischer Kennwerte auf die Eigenschaften von Blechformteilen

Influence of elastic material characteristics on the properties of forming parts Trends in the automotive industry tend towards safety, fuel saving and reduction of exhaust gas result in an increased application of high strength steels in the car body production. The sheet thickness can be reduced when using high strength steels but without reducing the load capacity. The forming of these steels is more difficult due to the special springback behaviour. Furthermore the dent resistance shows an important role especially for outer panel parts. One influencing factor on the material behaviour is the Young's modulus, which will be discussed in this paper.     

基材属性对铝蜂窝共面力学性能的影响

目的研究不同属性的基体材料对铝蜂窝共面压缩力学性能的影响。方法在保持正六边形蜂窝结构参数不变的情况下,改变基材属性,基体材料模型分别选择不同应变强化参数的双线性各向同性强化模型和理想弹塑性模型,建立相关可靠的有限元模型并进行大量的模拟计算。获得相应的变形模式和应力-应变曲线,对曲线进一步处理得到蜂窝共面静动态峰应力,并将结果以图表形式展示并分析。结果随着冲击速度的增加,样品依次出现了"X","V","一"字型3种变形模式,基体材料的应变强化效应使变形趋于均匀化;基体材料的应变强化效应显著增加了蜂窝的静态峰应力,对动态峰应力增量的影响可以忽略,对计算数据处理后得到了应变强化参数与动态峰应力的计算公式。结论基材具有强化特性的蜂窝,其共面静态力学性能优于基材为弹性理想塑性材料模型的蜂窝;在利用数值模拟的方法来研究蜂窝结构共面静态力学行为时,需要考虑基体材料的强化效应。     

复合材料夹芯梁屈曲破坏模式及极限承载

为研究复合材料夹芯梁在轴压作用下的屈曲、后屈曲特性及承载能力,进行了试验研究与有限元仿真。首先,开展了系列复合材料夹芯梁屈曲特性试验,研究了铺层比例、梁长度、表层厚度及芯层厚度等因素对其屈曲、后屈曲破坏模式及极限承载的影响;然后,基于非线性屈曲理论,采用三维内聚力界面单元模拟面芯脱粘,并引入初始预变形及材料损伤准则对复合材料夹芯梁在轴压下的屈曲特性及极限承载进行仿真研究。结果显示:界面脱粘是屈曲破坏的重要模式;仿真计算的极限承载与试验结果相比,误差控制在10%以内。所得结论表明该方法可有效预报复合材料夹芯梁的后屈曲路径、破坏模式及极限承载。