纳米颗粒增强镁基复合材料触变成形本构模型（英文）

通过分析纳米颗粒增强镁基复合材料半固态触变塑性成形中不同因素(应力σ、应变ε、应变速率ε、温度T、液相分数f_L、增强颗粒体积分数f_p)之间的关系,同时考虑Orowan增强机制,由此提出一种新的本构模型。该本构模型中各参数由多元非线性回归法演算而得。触变塑性成形实验数据与数值模拟数据吻合良好,证明推导的本构关系可用于触变塑性成形的数值模拟,并可用来指导复合材料的触变塑性成形工程实践。     

SiC_P/AZ61复合材料半固态触变成形的数值模拟

采用等温热处理法制备SiCP/AZ61复合材料半固态坯料。运用所建立的高固相SiCP/AZ61复合材料本构模型,对其触变成形过程进行数值模拟,得到成形过程中的应力和应变分布,并对比了触变成形和常规成形的成形特点。结果表明,SiCP/AZ61复合材料触变成形具有变形抗力小、应力分布均匀的特点。通过对比试验结果和模拟结果可知,两者吻合较好,所获结果可指导镁基复合材料触变成形工艺实践。     

SiC_P/AZ61复合材料的高温压缩变形本构方程

采用热压缩试验研究了SiC颗粒增强镁基复合材料在应变速率为0.1～10 s-1、变形温度为803～843 K时的热成形性能,并在实验数据分析的基础上根据真应力-真应变曲线,计算出复合材料的本构方程及变形激活能Q。结果表明,复合材料在高温下的流变应力较低,峰值应力与变形温度、应变速率之间的关系在低应力区符合指数关系。该复合材料的激活能随着应变速率的增大而增大。     

高固相率SiCP/AZ61复合材料触变成形的数值模拟

采用等温热处理法制备SiCP/AZ61复合材料半固态坯料,在自制实验装置上进行触变成形实验.采用所建立的高固相率SiCP/AZ61复合材料本构模型,对触变成形过程进行了数值模拟,得到了不同成形温度下的应力、应变和温度场分布.结果表明,与成形温度为530℃相比,560℃时复合材料触变成形具有变形抗力小、应变与温度场分布均匀的特点.通过实验和模拟结果对比可知(成形温度为560℃),两者吻合较好,所获结果可指导高固相率镁基复合材料触变成形工艺实践.     

变形镁合金触变锻造研究

采用机械搅拌法制备半固态变形镁合金,并设计制造了触变塑性成形装置,进行了变形镁合金触变锻造和常规锻造实验。采用所建立的半固态镁合金本构关系,对触变锻造进行了数值模拟,得到了成形过程中的应力和应变分布,对比了触变锻造和常规锻造的成形特点。结果表明,变形镁合金触变锻造具有变形抗力小、应力分布均匀的特点。通过实验和模拟结果对比可知,两者吻合较好,所获结果可指导变形镁合金触变锻造工艺实践。     

纳米SiC颗粒增强AZ61镁基复合材料制备工艺的优化

采用高能超声方法制备了纳米SiC颗粒增强AZ61镁基复合材料.利用正交试验法研究了纳米SiCN含量、超声导入温度和超声作用时间等关键工艺参数对纳米SiCp/AZ61镁基复合材料力学性能的影响.试验结果表明,纳米SiC颗粒含量对复合材料的抗拉强度和伸长率的影响最显著.在本试验条件下,超声制备纳米SiC颗粒增强AZ61镁基复合材料的最佳工艺方案可优选为:纳米SiC颗粒含量为1%、超声导入温度为650℃、超声作用时间为15min.     

半固态7050铝合金材料的触变力学模型

为了系统研究半固态7050铝合金的触变力学行为,采用Gleeble-3500热模拟试验机对SIMA法制备的半固态7050铝合金进行单向压缩试验,利用SPPS数理统计软件拟合材料本构模型,最后通过MSC.MARC软件进行半固态轧制过程的数值模拟。结果表明:7050铝合金的压缩流变应力与温度、应变速率以及应变具有相关性,在0.1~10 s-1的应变速率范围内,流变应力随温度的升高而明显降低,随应变速率和变形量的增大而增大;利用压缩试验测得真应力—真应变关系,可以建立半固态7050铝合金分阶段触变变形的粘塑性本构模型,该模型基于半固态材料的力学特性,并考虑液相分数的影响;模拟计算得到的稳态轧制力约为25 MPa,与实际轧制实验结果基本吻合,证明所建立的本构模型是合理的。     

触变注射成形法制备石墨烯纳米片增强镁基复合材料

采用触变注射成形的方法制备了石墨烯纳米片(GNPs)增强AZ91D镁基复合材料,利用OM、SEM、EDS、TEM和XRD研究了GNPs含量(0.3%、0.6%、0.9%,质量分数)对镁基复合材料微观组织的影响,并进行了力学性能测试。结果表明,GNPs在基体中呈条状均匀分布,与基体结合良好,GNPs的加入能够细化晶粒尺寸和减少孔隙。与AZ91D镁合金基体相比,GNPs的添加明显提高了复合材料的强度和硬度,当GNPs的含量为0.6%时,复合材料的力学性能最好,硬度和抗拉强度分别达到92.3 HV和245 MPa。     

SiCp/AZ61镁基复合材料的热膨胀性能研究

采用高能超声方法制备了SiCp增强镁基复合材料。论述了增强体、温度、增强体颗粒尺寸、增强体体积分数等对镁基复合材料热膨胀性能的影响。结果表明,增强体的加入可以减小镁基复合材料的热膨胀系数,镁基复合材料的热膨胀系数随温度的变化而变化,增强体的颗粒尺寸越小、体积分数越高,镁基复合材料的热膨胀系数就越小。     

原位合成TiC/AZ91复合材料力学性能的研究

采用重熔稀释法原位制备了不同质量分数的TiC颗粒增强的镁基复合材料,并对复合材料进行了力学性能测试。结果表明,原位合成的镁基复合材料的强度相比基体合金有了明显提高,塑性稍微降低。镁基复合材料强度的增加主要是因为位错强化、弥散强化和细晶强化协调作用的结果。     

半固态金属触变塑性成形上限法

在高固相率时,半固态金属的力学模型可简化为连续多孔体力学模型。针对半固态金属触变塑性成形的特点,本文发展了上限法理论在半固态金属触变塑性成形分析中的应用。提出速度间断值不仅要包括切向分量,还要包括法向分量。速度间断的法向分量是由金属通过速度不连续面时,材料固相率的变化而引起的。由此建立了半固态金属触变塑性成形的上限分析模型和理论方法,导出了上限功率的计算公式。为在实际触变塑性成形工艺分析中的进一步应用奠定了理论基础。     

AZ80镁合金热流变行为的Rosserd型本构描述

利用热物理模拟机Gleeble1500进行多组圆柱试样的热物理模拟压缩试验,试验温度为250～400℃,应变速率为0.01～10s-1。应用多元线性回归方法分析计算了AZ80镁合金唯象本构模型所需的一组系数,获得了能够较精确表示AZ80镁合金材料的流动应力与温度、应变速率和应变之间关系的Rosserd本构模型,为塑性成形模拟提供了所需的基本模型。     

An orthotropic ductile damage model for visco-plastic materials

Numerical modelling of bulk forming processes has to identify the conditions that may result in unsatisfactory products. In ductile materials, damage may occur with the micro void nucleation at the site of second phase particles and inclusions in the plastic or visco-plastic matrix and then with the micro void growth. In this work an isotropic ductile damage model is extended to load cases with successive tensile and compressive steps and with pure deviatoric stress state. The constitutive equations satisfy the Clausius-Duhem inequality for negative or positive voids volume fraction rate. The constitutive parameters are identified with the Rice and Tracey model modified for a sphere initially filled with a soft or a hard inclusion. Axisymmetric geometries are considered for remote strain fields without distortion. A plane cell and a 3D unit cell are analysed numerically for the deviatoric strain state and various combined deviatoric and volumetric deformations.     

Implementation of VPSC polycrystal model into rigid plastic finite element method and its application to Erichsen test of Mg alloy

A methodology on the multiscale simulation of metal forming processes is presented, which fully integrates the visco-plastic self-consistent (VPSC) polycrystal model into rigid plastic finite element method (FEM). To accurately predict the material behavior of a magnesium alloy from the microstructural level, the VPSC crystal plasticity model was used as a constitutive equation in this methodology. An optimization program VPSC-GA was developed in order to calculate the hardening parameters for each slip and twin mode of a single crystal from a couple of simple tension/compression tests. The existing constitutive equation for rigid plastic FEM is modified using the deviatoric stress components and the derivatives of them with respect to strain rate components. The stiffness matrix and the load vector were derived based on a new approach and implemented into DEFORM^TM-3D via a user subroutine which handles stiffness matrix in elemental level. An application to the Erichsen tests of magnesium alloys was done and the stretch formability of two different Mg alloy sheets was analyzed using the results of both experiment and simulation.     

Effect of microporosity on the tensile properties of AZ91 magnesium alloy

The effect of microporosity on the tensile deformation of as-cast AZ91 magnesium alloy was investigated through systematic experimental approaches and theoretical predictions of a constitutive model for tension instability. The strain rate sensitivity was measured at room temperature by the incremental strain rate change test, and the microporosity was quantitatively obtained by fractography analysis on fractured surfaces. The tensile strength and elongation of as-cast AZ91 alloy have a strong inverse parabolic dependence on microporosity variation. The constitutive model can exactly predict the tensile deformation of AZ91 alloy through a practical estimation of strain-related terms and load carrying capacity by quantitative fractography. The overall plastic deformation of AZ91 alloy depends fundamentally upon not only the variation of load carrying capacity, but also on the strain hardening exponent and strain rate sensitivity. The contribution of strain rate sensitivity to plastic deformation becomes increasingly significant with a decreased strain hardening ability. As the strain rate sensitivity of the conventional material is very low but not zero, the constitutive model for the exact prediction of plastic deformation should take the strain rate sensitivity term into account.     

7075铝合金的热激活变形行为与唯象本构关系

利用热物理模拟机Gleeble1500进行多组圆柱试样的热物理模拟压缩试验,试验温度为250～450℃,应变速率为0.01～10 s-1.结果表明,7075铝合金热压缩温度在300、350、400和450℃时流变行为呈近稳态,而在250℃时呈非稳态.应用多元线性同归方法分析计算了7075合金唯象本构模型所需的一组系数及热变形的激活能.获得了能够较精确表示7075合金材料的流动应力与温度、应变速率和应变之间关系的唯象本构模型,为塑性成形模拟提供了所需的基本模型.     

Effect of strain rate on the forming behaviour of sheet metals

The strain rate dependence of plastic yield and failure properties displayed by most metals affects energies, forces and forming limits involved in high speed forming processes. This paper investigates the influence of the strain rate on the forming properties of one laboratory made and three commercial steel grades: a CMnAl TRIP steel, the ferritic structural steel S235JR, the drawing steel DC04 and the ferritic stainless steel AISI 409. First, split Hopkinson tensile bar (SHTB) experiments are carried out to assess the influence of the strain rate on the materials’ stress-strain curves. Subsequently, the obtained SHTB results, together with static tensile test results, are used to model the constitutive behaviour of the investigated steels using the phenomenological Johnson-Cook (JC) model and the Voce model, thus allowing dynamic modelling of forming processes. Finally, forming limit diagrams (FLDs) are calculated using the Marciniak-Kuczynski method. The results clearly show that the effect of the strain rate on forces and energies involved in a forming process, and the forming limits is non-negligible and strongly material dependent.     

A constitutive model for spring-back prediction in which the change of Young's modulus with plastic deformation is considered

In order to improve the prediction capability of spring-back in the computational analysis of sheet metal forming processes, a stress–strain constitutive formulation of non-linear combined hardening rule has been proposed in this paper according to non-linear kinematic hardening theory of Lemaitre and Chaboche and Hill's 1948 anisotropic yielding function. Traditionally, Young's modulus is considered as a constant in engineering application and numerical simulation. In fact, it decreases with plastic deformation. So the effect of the change of Young's modulus with plastic strain on spring-back is considered in the constitutive model. The algorithm of stress update is elastic prediction, plastic correcting and radial returning. Numerical results and experimental results show that the proposed constitutive model significantly improves the prediction accuracy of spring-back.     

高应变速率下铝、铜合金弹、塑性本构关系的试验研究

本文通过旋转盘式冲击试验 ,对铝、铜合金在高应变速率下弹塑性本构关系进行探讨 ,此研究对高速变形研究奠定了基础     

纯铁在高应变率下的流动应力特征及其动态塑性本构关系

利用MTS材料试验机和分离式Hopkinson压杆实验装置,对锻造后经930℃下退火2h的纯铁材料进行压缩实验,测定纯铁在准静态条件(10-3s-1~100s-1)和高应变率(650s-1~8500s-1)下的应力-应变曲线。实验结果表明,纯铁是应变率敏感材料,纯铁在高应变率条件下,具有应变率增强、增塑以及应变强化效应,高应变率下的塑性变形过程中产生的绝热升温对材料具有热软化作用。基于Johnson-Cook(J-C)本构模型,引入绝热温升软化项对模型进行修正,通过实验数据拟合得到了纯铁的动态塑性本构关系,模型计算结果和实验结果证明,该模型可以较好地预测纯铁在高应变率下的塑性流动应力。