金属材料塑性应变比r值的测试

ISO10113：2006及GB／T5027-2007规定,对于不均匀塑性应变材料,采用线性拟合回归方法测试塑性应变比,并设定必须通过原点的边界条件。分别采用单点法、过原点线性回归法（设定截距为0）及常规线性回归法（不设定任何边界条件）3种测试方法计算分析了均匀塑性应变材料和不均匀塑性应变材料的r值,并进行比较,探讨了线性回归法设定边界条件的合理性。结果表明：对于均匀塑性应变材料,单点法、过原点线性回归法和常规线性回归法均可准确地分析其r值;对于不均匀塑性应变材料,只能采用常规线性回归法分析其r值,而不能采用单点法和过原点线性回归法分析其r值。     

金属薄板塑性应变比测量不确定度的评定

从试验方法上对塑性应变比r值的测量不确定度进行了评定,并对试样尺寸测量和引伸计等方面引起不确定的因素进行了讨论和计算.在评定合成不确定度时,应根据塑性应变比r值的计算公式计算各不确定度分量的灵敏系数;当输入量明显相关时,计算公式中应考虑相关系数的作用.     

ISO 10113:2020存在的问题及GB/T 5027—2016的修订建议

针对符合标准ISO 10113:1991和ASTM E517要求的自动测量塑性应变比(r值)的设备不符合ISO 10113:2020标准要求的问题，按照合成标准不确定度的公式分析了ISO 10113:2020计算r值的测量不确定度和ISO 10113:1991计算r值的测量不确定度。结果表明：ISO 10113:2020计算r值的合成标准不确定度大于ISO 10113:1991计算r值的合成标准不确定度；重新修订的GB/T 5027—2016应该同时要满足ISO 10113:2020和ASTM E517的要求。     

测定塑性应变比的区间回归方法与力学解析

以复相高强钢Trip600与深冲成形用DC04钢板材为材料,介绍了ISO 10113标准测定r值的回归方法,并探讨了与常规单一应变数据对求解r值方法的相关特性.试验表明,采用单点法测定r值时,平行试样间及不同试验机结果间的离散性较大,且r值与应变呈现显著的路径特征.屈服变形、纵向与横向引伸计在试验初始时刻的延迟效应及速度切换时的惯性效应是应变测量误差的重要来源,采用回归方法可以有效消除这些系统与或随机误差的累积.考虑引伸计系统因上述不稳定效应造成的不同步现象,当采用拟合方法时,拟合直线不应设定通过原点的边界条件.     

“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。     

试样尺寸对钢板塑性应变比r的影响

选用三种尺寸的拉伸试样测试塑性应变比（r值）。通过试验和数据分析,得出当试验标距接近试样平行长度时,r值将下降。其原因是当标距接近试样平行长度时,试样标距内的应变是不均匀的。     

金属薄板的区间r值及其应用

材料的锯齿屈服效应以及低应变水平下塑性应变比r值应变路径存在的奇异性会造成r值测试结果的明显离散,给材料性能的准确评价带来较大的困难,而区间r值可以较好地解决该类离散问题,在结果的重复性方面显现出独特优势。在区间r值的计算过程中,宽度和长度方向的真塑性应变ε_b和ε_L线性回归后得到的直线是否强制通过坐标原点,会导致部分测试结果的差异,但大部分情况下该差异并不显著,仅就重复性而言,目前无法确认是否应该设置边界条件。     

基于应力功恒等法的振动时效研究

振动时效主要用于消减构件的残余应力,本质上类似于应力松弛,应变变程恒定的情况下峰值应力随周期减小。材料发生应力松弛的部分为应力集中区,振动时效过程中产生局部塑性应变。针对如7075高强铝合金幂次硬化材料,可以采用基于等效线弹性模型的应力功恒等法近似计算材料的局部应力和应变变程,以弥补实验过程需要测量但不易获得的重要数据。计算得到的应力-应变曲线与流变塑性理论公式推导的结果及其它研究者通过模型仿真得到的结果相似,表明应力功恒等法应用于振动时效分析具有计算简单,准确实用的特点,对工程实践有一定的参考价值和指导作用。     

“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。测定金属材料薄板和薄带塑性应变比(r值)的现行国家标准是GB/T 5027—2016     

水泥砂浆流变学性能的评价方法

提出Ｕ型流动法评价水泥砂浆塑性粘度,运用流变学对Ｕ型流动法作了理论分析。结果表明,当浆体的剪应力屈服值较小时,该方法的测量参数与浆体的塑性粘度之间有线性关系。该方法可用来评价预填骨料混凝土用砂浆及其它剪应力屈服值较小的Ｂｉｎｇｈａｍ体的塑性粘度。     

Microstructural modeling and simulation for GCr15 steel during elevated temperature deformation

The microstructural evolution of GCr15 steel, one of the most commonly used bearing steels, was investigated and simulated by physical experiments and finite element method (FEM). Physical experiments were conducted on the Gleeble-3500 thermo-simulation system. Effects of initial grain size and plastic strain on the microstructural of the materials were investigated by setting different heating temperature, holding time and deformation degree, respectively. Based on the results of stress–strain curves and metallographic analysis, the constitutive equations for flow stress, austenite grain growth and dynamic recrystallization of GCr15 steel were formulated by linear regression method and genetic algorithm. In addition, the coupled thermo-mechanical finite element method integrated with the developed constitutive models was used to simulate the microstructural evolution of GCr15 steel during hot compression. Good agreement between the calculated and experimental results was obtained, which confirmed that the developed constitutive models can be successfully used to predict microstructural evolution during hot deformation process for GCr15 steel.     

拉伸应变硬化指数的测试及方法比较

针对IS010275：2007及GB／T5028-2008中对于材料在拉伸时呈现锯齿屈服效应曲线如何计算拉伸应变硬化指数n值的问题，就未呈现锯齿屈服效应的曲线和呈现锯齿屈服效应的曲线，采用国际线性回归法计算行nline ，并用Zwick试验机采用回归法测试行ntest 以及用差分平均法测试nsingle，同时对三种测试方法进行比较。结果表明：对于不呈现锯齿屈服效应的曲线，可以同时采用上述三种方法；而对于呈现锯齿屈服效应的曲线，不能采用差分平均法测试nsingle，只能采用国际线性回归法计算nline 以及采用Zwick试验机用回归法测试nrest。且对于呈现锯齿屈服效应的曲线测试nline和ntest，回归区间不宜太小。     

两种方法测定冷轧薄板应变硬化指数、塑性应变比值和伸长率的结果比较

借助两种不同的方法，测定了冷轧薄板的应变硬化指数（n）、塑性应变比（r）值和伸长率。在GALDABINI SUN1000试验机上，用光学非接触引伸计在GRAPHWORK 1软件上实现冷轧薄板的n和r值及伸长率的自动测量；在INSTRON1186试验机上，用YYU5050引伸计在LZC软件上自动测量冷轧薄板的n值，手工测量r值和伸长率。将两种方法得到的试验结果进行比较，发现两种方法的结果非常接受。用光学非接触引伸计在GRAPHWORK1软件上自动测量的n和r值及伸长率具有较高的可靠性和重现性。     

Development of numerical scheme for phase field crystal deformation simulation

The phase field crystal (PFC) method is anticipated as a new multiscale method, because this method can reproduce physical phenomena depending on atomic structures in metallic materials on the diffusion time scale. Although the PFC method has been applied to some phenomena, there are few studies related to evaluations of mechanical behaviors of materials by appropriate PFC simulation. In a previous work using the PFC method, tensile deformation simulations have been performed under conditions where the volume increases during plastic deformation. In this study, we developed a new numerical technique for PFC deformation simulation that can maintain a constant volume during plastic deformation. To confirm that the PFC model with the proposed technique can reproduce appropriate elastic and plastic deformations, we performed a series of deformation simulations in one and two-dimensions. In one- and two-dimensional single-crystal simulations, linear elastic responses were confirmed in a wide strain rate range. In bicrystal simulations, we could observe typical plastic deformations due to the generation, annihilation and movement of dislocations, and the interaction between the grain boundary and dislocations. Moreover, the deformation behaviors of a nanopolycrystalline structure at high temperature were simulated and the intergranular deformations caused by grain rotation and grain boundary migration were reproduced.     

Calculation of yield stresses and plastic strain ratios

Yield stresses and plastic strain ratios of aluminium, copper, brass and steel sheets having various textures, which are characterized by the orientation distribution functions, have been calculated as a function of angle to the rolling direction using the Bunge method based on Taylor's minimum energy theory and another method suggested by the present authors. The calculated results are compared with the measured ones. For steels, the two methods yield almost identical yield stress results. The Bunge method yields higher average plastic strain ratios than the measured data, while their variation with the angle to the rolling direction agrees very well with the measured values. The plastic strain ratios calculated by the second method are in very good agreement with the measured data in their average values but show smaller variations with the angle to the rolling direction than the measureD. Therefore, combination of the two methods can yield very good agreement between calculated and measured plastic strain ratios. For the f c c metals, the calculated yield stresses and plastic strain ratios are in good agreement with measured data, regardless of the calculation method.     

Linear and nonlinear torsional behavior of unidirectional CFRP and GFRP

The helicopter bearingless rotor flexbeam is usually made of glass-fiber reinforced plastic composite (GFRP). Carbon-fiber composites (CFRP) are candidate for future flexbeam materials due to their superior tensile fatigue strength. This research examines the feasibility of CFRP as a future flexbeam material. The torsion behaviors of unidirectional CFRP and GFRP with the same matrix resin were investigated. As a result, it was confirmed that the behavior of both CFRP and GFRP is comprised of linear/nonlinear domains. The initial torsional rigidity of CFRP was almost the same as that of GFRP. The torsional rigidities calculated from Lekhnitskii’s equations agreed with the experimental results, and they are mainly determined by the shear stiffness of the materials. The nonlinear torsional behavior was observed above 0.5% of the shear strain, and it is due to plastic deformation of the matrix resin. A 3D plasticity model proposed by Sun et al. was applied to the plasticity parameters obtained from off-axis tensile tests. The numerical curves agree with the experimental data below 1.5% of the shear strain. The experimental result suggests that GFRP can be replaced by CFRP as torsional elements of a helicopter flex beam without an increase in torsional rigidity.     

Deformation behaviour of bulk materials during repetitive upsetting-extrusion (RUE)

Repetitive upsetting-extrusion (RUE) that was originally invented to process powder materials for bulk mechanical alloying is currently being used to process bulk materials. Bulk materials are subjected to severe plastic deformation using the same die design that was used to process powder materials. As the deformation behaviour of powder and bulk materials are quite different, it has to be evaluated whether a single die design is suitable to process both these materials. Further, information on the deformation behaviour and strain homogeneity that can be achieved by subjecting bulk materials to RUE process are also currently not available. To address these issues, both numerical analysis and actual experiments on commercial pure copper has been carried out. The results obtained are presented and discussed here