Development of a biaxial tensile machine for characterization of sheet metals

A new stand-alone biaxial testing machine with out-of-plane loading system has been developed to study the anisotropic plastic behavior of metal sheets on cruciform specimens. In this apparatus a single screw driven actuator is used and the variation of the load ratio along the two main directions is achieved by adjusting the geometry of a link mechanism. This design firstly combines the advantages of biaxial displacement devices, typically mounted in a universal tensile tester, with stand-alone machines and by at the same time providing a solution to the limitations associated with each of these types. The used specimen is discussed and compared through numerical simulations to a prominent geometry proposed in the literature. Experiments are presented and the results are implemented in identifying classical and advanced yield criteria and though represented as yield surfaces.     

拉伸比对2A16铝合金板材双向拉伸性能的影响

为获取2A16铝合金板料在复杂加载条件下的材料性能,设计了一种臂上开缝、中心带槽的十字形试样并开展双向拉伸试验,研究了2A16铝合金板材在双向加载时的材料力学性能.建立有限元分析模型,基于ABAQUS软件对十字形试样的双向拉伸过程进行数值模拟.同时,利用板材双向拉伸试验机在X、Y两轴拉伸比分别为3∶3、3∶2、3∶1、...     

Accurate stress computation in plane strain tensile tests for sheet metal using experimental data

The advances achieved in phenomenological constitutive laws and their implementation in finite element codes for predicting material behavior during forming processes have motivated the research on material identification parameters in order to ensure prediction accuracy. New models require experimental points describing a bi-axial stress state for proper calibration, and the features of the plane strain tensile test have made it one of the most used. The test's principal inconvenience is the influence of the free edges on strain field homogeneity and stress computation.     

Yield locus evolution and constitutive parameter identification using plane strain tension and tensile tests

An inverse calibration strategy to determine the constitutive parameters of phenomenological advanced yield criteria in a convenient and economical manner is presented. The studies on the shape of the yield loci for various steel types revealed that their work contours exhibit almost no evolution in the vicinity of the equibiaxial tension after roughly 4% equivalent strain. In other words, the ratio between balanced biaxial and uniaxial stresses of the yield locus reaches a saturation value after undergoing some deformation. Accordingly, the balanced biaxial stresses can be associated with the tensile flow stresses in the rolling direction by means of a constant factor, which can be generalized for different steel families. Based on this, an alternative inverse-analysis strategy using the tensile and plane strain tension tests will be proposed and validated within this work. Cup drawing tests have been applied to assess the accuracy of the optimized yield loci for different strain paths.     

BH220钢板屈服轨迹的双向拉伸实验研究

本文针对建立的十字形双向拉伸试验系统 ,利用有限元模拟优化得到的十字形试件 ,采用载荷控制方式对汽车用薄钢板BH2 2 0进行了不同加载路径下的双向拉伸试验 ,得到了不同加载路径下的应力应变关系曲线 ,并根据塑性功相等的原则 ,对BH2 2 0钢板的试验屈服点与现有屈服准则Hill4 8、Barlat lian、Logan hosford的理论轨迹进行了对比 ,结果表明 ,与试验结果相比 ,Hill4 8过高地估计了屈服轨迹 ,Logan hosford准则比Barlat lian准则接近试验结果 ,尤其在垂直于轧制方向与试验结果吻合较好 ,但在靠近轧制方向其理论轨迹偏高。     

一种金属箔材双向拉伸试验方法

用常规的单轴拉伸试验难以获得箔材机械性能的准确数据 ,目前采用的一些双向拉伸试验方法还存在着各自的不足。本文提出并详细介绍了一种金属箔材双向拉伸试验方法。在平膜鼓胀装置上 ,通过测量膜片极顶的面内真应变和横向塑性应变以及膜片的轮廓形状 ,并计入泊松比随变形过程发生的变化 ,可建立二向应力状态下箔材从弹性经塑性至破裂的整个变形范围内真应力和真应变的关系 ,同时还可以得到弹塑性泊松比和塑性泊松比的变化规律     

Experimental determination of yield loci for magnesium alloy AZ31 under biaxial tensile stress conditions at elevated temperatures

The finite element analysis (FEA) has become one of the most relevant and most important tools in fields of sheet metal forming for designing processes and dimensioning parts. However, reliability and quality of the numerical results strongly depend on the whole FE-model and especially on the modeling of the material behavior, which shows wide impact on calculated stresses and strains of sheet metal parts. Therefore, the experimental determination of characteristic material data concerning anisotropic and temperature-effects is essential. In this paper the influence of temperature on the yielding and the hardening behavior of the magnesium sheet metal alloy AZ31 are investigated for different uniaxial and biaxial stress conditions. For that purpose an experimental setup has been developed at the Chair of Manufacturing Technology (LFT) which enables biaxial tensile testing of sheet metal. Yield loci of AZ31 are determined as a function of temperature and they are based on solely measurement data of the forming process itself.     

Mises准则的圆形屈服轨迹及其在板料成形中的应用

按Ｍｉｓｅｓ屈服准则求解板料成形问题,理论严密,结果准确。本文提出了一种Ｍｉｅｓ准则的圆形屈服轨迹图。利用这种圆形屈服轨迹图求解轴对称板料成形问题,可使求解过程简化,使求解结果更加清晰,直观。与传统的椭圆屈服轨迹比较,有明显的改进。     

单向拉伸试验研究AZ31B镁合金板材的电塑性效应

通过单向拉伸试验研究镁合金 AZ31B 的电塑性效应。为了显示脉冲电流的非热效应,在相同温度下开展两类试验：环境箱中的单向拉伸试验和脉冲电流辅助的单向拉伸试验。此外,对脉冲电流在材料变形过程中引起的温度场进行数值模拟。结果表明,沿材料截面方向温度分布均匀。通过对比两类单向拉伸试验的真应力?真应变曲线,证实了脉冲电流非热效应的存在。通过光学显微镜研究脉冲电流对材料微观组织演化的影响,结果表明：脉冲电流引起的动态再结晶对流动应力的下降起重要作用。最后,提出一个考虑电塑性响应的 AZ31B 流动应力模型,并通过实验进行验证。结果表明：模型预测结果和实验结果吻合较好。     

Determination of the flow stress of five AHSS sheet materials (DP 600, DP 780, DP 780-CR,DP 780-HY and TRIP 780) using the uniaxial tensile and the biaxial Viscous Pressure Bulge (VPB) tests

Room temperature uniaxial tensile and biaxial Viscous Pressure Bulge (VPB) tests were conducted for five Advanced High Strength Steels (AHSS) sheet materials, and the resulting flow stress curves were compared. Strain ratios (R-values) were also determined in the tensile test and used to correct the biaxial flow stress curves for anisotropy. The pressure vs. dome height raw data in the VPB test was extrapolated to the burst pressure to obtain the flow stress curve until fracture. Results of this work show that the flow stress data can be obtained to higher strain values under biaxial state of stress. Moreover, it was observed that some materials behave differently if subjected to different state of stress. These two conclusions, and the fact that the state of stress in actual stamping processes is almost always biaxial, suggest that the bulge test is a more suitable test for obtaining the flow stress of AHSS sheet materials for use as an input to Finite Element (FE) simulation models.     

Evaluation of stress intensity factors of thin AZ31B magnesium alloy plate under biaxial tensile loading

Stress intensity factors of thin AZ31B magnesium alloy sheet under biaxial tension loading were analyzed by modified Dugdale model.K-values with crack angle of 90°obviously show that there is no influence of the loading condition in Mode-I.In the 45°case,K Ⅰ values are obtained within 10%errors when they are calculated by modified Dugdale model under biaxial loading.It is concluded that the modified Dugdale model is one of effective ways to evaluate stress intensity factor of AZ31 magnesium alloy sheet appropriately.     

High-rate tensile properties of Si-reduced TRIP sheet steels

There have been efforts to develop Si-reduced TRIP steels to improve the wettability of Zn coatings, since the conventional CMnSi-TRIP steels suffer from poor galvanizability. In addition, for the development of potential applications of Si-reduced TRIP steels in vehicle crash management, a better understanding of high strain rate properties is required. In the present study, the effects of alloying elements, such as Cu, Al, Si, and P, on the high-rate tensile properties of Si-reduced TRIP sheet steels were investigated. Tensile tests were performed with a servo-hydraulic tensile testing machine at strain rates ranging from 10⁻² to 6 × 10² s⁻¹, and the ultimate tensile strength, elongation, strain rate sensitivity, and absorbed energy were evaluated. The retained austenite volume fractions and carbon content of the specimens were measured using neutron diffraction. The UTS was increased with Cu, Al, Si, and P alloying throughout the strain rate range, and the alloying effect on UTS was considerable with Cu and P. The effects of alloying on the microstructure were not significant. All the steels tested in this study exhibited positive strain rate sensitivity, and the m value at strain rates higher than 10 s⁻¹ was at least two times higher than that at lower strain rates.     

The influence of the crystallographic texture on the biaxial stretchability of AA 5182 sheet

Crystallographic texture plays an important role in mechanical anisotropy. For a sheet material in biaxial stretching, texture has a significant effect on the formation of strain localization. In this work, the effects of different textures on the biaxial stretchability of AA 5182 sheet materials were studied. The results indicate that for textured AA 5182 sheet materials, the biaxial stretchabilities were closely associated with the crystallographic texture. It was found that the Olsen cup values were closely correlated to the calculated strain path values and limit strains. For a sheet material with a proper texture combination, the biaxial stretchability is greatly improved.     

薄壁曲面塑件加工工艺

分析了薄壁曲面塑件的工艺特点,采用分段加工工艺原理,优化了数控加工工艺及刀具路径,详细编制了塑件的正反面加工工艺,提高了塑件的加工效率和加工质量。     

Anisotropic behavior of deep-drawn al 1017 alloy using Macroscopic tensile and cupping tests

This paper presents a macromechanical approach for the determination of microstructural integrity of aluminum 1017 alloy (vis-à-vis recrystallization, recovery, and grain growth). Tensile and cupping tests were carried out on cold-rolled 1.2 mm and 1.6 mm samples. The paper examines the variation of the plastic strain ratio, dislocation density, degree of deformation, and ultimate tensile strength of this alloy in relation to the orientation of rolling using macromechanically based stress and strain models.     

冷轧深冲板塑性应变比和屈服应力的理论计算及试验验证

采用金属薄板的单向拉伸试验方法,测定了DC04和DC05板料在0°、45°、90°方向的屈服应力及Hill塑性应变比,并结合Hill48各向异性屈服理论,建立了预测任意方向屈服应力和Hill塑性应变比的理论计算模型,分析了其在0°、15°、30°、45°、60°、75°和90°方向的理论值和实验值的偏差。结果表明DC04和DC05板料的Hill塑性应变比的理论值和试验值的偏差均不超过3.5%,且在0°、45°、90°这3个方向上没有偏差;屈服应力的理论值和试验值的偏差均不超过2.6%,且DC04板料的最小偏差出现在45°方向仅为0.84%,DC05板料的最小偏差出现在0°和15°方向仅为0.51%。说明应用Hill48屈服理论计算DC04和DC05板料的屈服应力和Hill塑性应变比是十分准确的。     

几种屈服准则的屈服应力的比较分析

通过对几种屈服准则的屈服应力的比较分析,找出了它们的差异。通过对理论屈服值的比较得知,选取Tresca屈服准则最为经济,选取双剪屈服准则最为安全,这对实际工程应用具有一定的参考价值。