Research on the sticking-sliding contact ratio in high-speed cutting of cupronickel B10

Journal of Mechanical Science and Technology - Accurate understanding of the frictional behavior at the tool-chip interface is critical for the cutting process. To quantitatively analyze the ratio...     

Identification of material parameters in constitutive model for sheet metals from cyclic bending tests

This paper deals with the identification of material parameters in a constitutive model for sheet metals using the bending moment versus curvature diagrams obtained by cyclic bending tests. The model can describe the cyclic strain hardening by the isotropic hardening and the Bauschinger effect by the kinematic hardening. An optimization technique based on the iterative multipoint approximation concept was used for the identification of the material parameters. This paper describes the experimentation, the fundamentals and the technique of the identification problem, and the verification of this approach.     

A new constitutive model of rubber

A new constitutive model of rubber is proposed based on the kinetics of elastic moduli. The model describes both linear and non-linear behaviour of rubber as well as rupture of inner bonds. In particular, it describes the well-known Mullins and Payne effects. It can be used for simulating both friction and wear of rubber.     

阀门用辅助材料工作温度的选择

阀门的工作温度,不仅与阀门主体材料有关,还与阀门使用的辅助材料有关。根据相关标准和资料,对阀门常用辅助材料的适宜工作温度作了介绍。     

10B06冷镦钢连铸坯的热压缩流变行为

利用MMS-200型热力模拟试验机研究了10B06冷镦钢连铸坯在750～1 100℃、应变速率为0.01～20s-1条件下的热压缩流变行为,并且通过线性回归确定了该钢的应变硬化指数以及热激活能,获得了其在变形条件下的流变应力本构方程。结果表明:该钢在热压缩变形时的流变软化行为是动态再结晶、动态回复与加工硬化联合作用的结果;当变形温度较低、应变速率较小时,软化效应以动态再结晶为主;而当变形温度较高、应变速率较大时,软化效应是动态再结晶和动态回复共同作用的结果;该钢的流变应力可采用Zener-Hollomon参数的函数来描述,其热激活能为220.132 3kJ.mol-1。     

Deformation analysis of micro-sized material using strain gradient plasticity

To reflect the size effect of material (1–15 μm) during plastic deformation of polycrystalline copper, a constitutive equation which includes the strain gradient plasticity theory and intrinsic material length model is coupled with the finite element analysis and applied to plane strain deformation problem. The method of least square has been used to calculate the strain gradient at each element during deformation and the effect of distributed force on the strain gradient is investigated as well. It shows when material size is less than the intrinsic material length (1.54 μm), its deformation behavior is quite different compared with that computed from the conventional plasticity. The generation of strain gradient is greatly suppressed, but it appears again as the material size increases. Results also reveal that the strain gradient leads to deformation hardening. The distributed force plays a role to amplify the strain gradient distribution.     

Microforming at elevated temperature - forming and material behaviour

Manufacturing of metallic parts by forming methods is industrially widespread due to several advantages like good surface quality, high accuracy and good efficiency at concurrent high quantity. As a result of the steady miniaturisation of products, large quantities of smallest metallic parts with the above mentioned attributes are needed. Despite the advantages of forming methods, microparts are mainly produced by machining, because of problems caused by so-called size-effects. These effects occur by scaling down geometry and process parameters, leading to the fact that the existing know-how for conventional processes cannot be transferred unrestrictedly to microscale. One reason for the difference between macro- and microscale is the number of grains within the forming area. At microscale only a small number of grains are directly involved in the forming process, so that the single grain, characterised by its individual size, orientation and position, gains influence on the process. The stochastic distribution of the grain characteristics leads to an inhomogeneous material behaviour and causes an increased scatter of the process parameters. To minimise the effect of inhomogeneous material behaviour, microforming at elevated temperature is applied. Experiments with different materials at elevated temperature show a homogenising effect which leads to a reduced process scattering. This indicates that elevated temperatures are suitable to minimise and control the size-effects at microforming processes. Additionally an enlargement of the forming limits by microforming at elevated temperature is observable.     

Thermal property of insulating material at cryogenic temperature

The thermal property of insulation material is essential in developing high temperature superconductor (HTS) devices operating at around liquid nitrogen temperature. Unlike metallic materials, nonmetallic materials have a thermal resistance; therefore, accurate estimate of the heat flow is difficult in the case of nonmetallic materials. In this study, a precise instrument is developed for measuring the thermal property of insulating materials over a temperature range of 30 K to approximately the room temperature by using a cryocooler. The cold head of the cryocooler is thermally anchored to the thermal link and used to cool the apparatus to a desired temperature. The temperature distribution in specimen is measured with respect to the supplied heating power, from which the thermal conductivity is calculated and compared with published data for accuracy confirmation. The effective thermal conductivity of polypropylene laminated paper (PPLP) is presented and the trend in the behavior of conductivity near liquid nitrogen temperature is also discussed.     

Deformation path and springback behavior in double-curved bending at high temperature

In this work, integrated double-curved bending-sizing-unloading is simulated for a Ti6Al4V titanium alloy sheet. Bending radii R30 mm × R30 mm and R30 mm × R15 mm are used in the bending tests at 700 °C and 750 °C, respectively. A holding time of 0–600 s is applied to explore the effect of sizing time on forming accuracy. Similar experimental tests are performed for comparison with the finite element analysis results. Results show that bending behavior varies remarkably with the bidirectional radii. As for equal bidirectional curvature, bending along each direction occurs simultaneously. Given that bidirectional radii are different, the sheet consecutively experiences single small-, single large-, and double-curved bending. The deformation path results in nonuniform plastic strain distribution. The springback amount increases from the center to the marginal middle zone. Sizing at 700 °C or 750 °C in 600 s or 180–600 s can remarkably reduce the springback amount, respectively. The springback prediction via finite element method is consistent with that of the experiment.

     

A continuum plasticity model for the constitutive and indentation behaviour of foamed metals

A yield surface is proposed that can be fitted to the plastic flow properties of a broad class of solids exhibiting plastic compressibility and different yield points in tension and compression. The yield surface is proposed to describe cellular solids, including foamed metals, and designed to be fitted to three experimental results: (1) the compressive stress–strain response (including densification), (2) the difference between the tensile and compressive yield points and (3) the degree of compressibility of the foam, as measured by the lateral expansion during a uniaxial stress compression test. The model is implemented using finite elements and used to study the effects of plastic compressibility on two problems: the compression of a doubly notched specimen and indentation by a spherical indenter. The model is then fitted to the properties of a typical closed cell aluminum foam and used to study indentation into a dense aluminum face sheet on a foam foundation. The dependence of the indentation load–displacement curve on the relevant material and geometric parameters is determined, and a single load–displacement relation is presented which approximates the behaviour of a wide range of practical designs. These results can be used to design against indentation failure of sandwich panels.     

Influence of constitutive model in springback prediction using the split-ring test

The aim of this paper is to compare several plastic yield criteria to show their relevance on the prediction of springback behavior for a AA5754-0 aluminum alloy. An experimental test similar to the Demeri Benchmark Test [Demeri MY, Lou M, Saran MJ. A benchmark test for springback simulation in sheet metal forming. In: Society of Automotive Engineers, Inc., vol. 01-2657, 2000] has been developed. This test consists in cutting a ring specimen from a full drawn cup, the ring being then split longitudinally along a radial plan. The difference between the ring diameters, before and after splitting, gives a direct measure of the springback phenomenon, and indirectly, of the amount of residual stresses in the cup. The whole deep drawing process of a semi-blank and numerical splitting of the ring are performed using the finite element code Abaqus. Several material models are analyzed, all considering isotropic and kinematic hardening combined with one of the following plasticity criteria: von Mises, Hill’48 and Barlat’91. This last yield criterion has been implemented in Abaqus. Main observed data are force-displacement curves during forming, cup thickness according to material orientations and ring gap after splitting. The stress distributions in the cup, at the end of the drawing stage, and in the ring, after springback, are analyzed and some explanations concerning their influence on springback mechanisms are given.     

BH10Mn2G焊接用钢的热变形行为

利用Gleeble-1500型热模拟试验机研究了BH10Mn2G焊接用钢在温度为900～1 050 ℃、应变速率为0.10～10 s-1条件下的热变形行为,并进行了相关计算.结果表明:BH10Mn2G钢的动态再结晶激活能Q=301.11 kJ/mol,热变形方程为Z=3.281×1010 exp(0.039 73σm),并得到了动态再结晶状态图;这为合理预报和控制BH10Mn2G焊接用钢的组织和性能提供了基本依据.     

10cm地温数据异常分析及仪器故障排除

地温资料数据量大,其数据异常情况较为隐蔽,利用RTD图形显示分钟资料,可较快发现数据跳变。文章以德庆自动气象站2011-07-31的10cm地温数据异常的分析处理为实例,用排除法找出了仪器故障点,提出了提高地温数据质量的改进措施。     

A phenomenological constitutive model for the pseudoelastic behavior of shape memory alloys

Shape memory alloys (SMAs) possess the distinctive ability to recover large mechanically-induced inelastic strains upon unloading, which is known as the pseudoelastic behavior. This paper deals with an extension of the phenomenological viscoplasticity theory, which has been developed by the author to depict the negative strain rate sensitivity, to model the macroscopic behavior of the phase transformation. Unlike most phenomenological models for the pseudoelasticity, the proposed model does not employ a kinetic law describing the evolution of the martensitic volume fraction and the transformation loading and unloading conditions but introduces two internal state variables concerned with the evolution of the elastic modulus and the back stress. The applicability of the constitutive model to SMAs is validated by comparing simulation results with experimental data on uniaxial and torsional loading reported in the literature. And then it is demonstrated that the same constitutive equations can be applied to model the highly nonlinear unloading behavior of solid polymer.     

Modeling mechanical response of intumescent mat material at room temperature

Intumescent mat material is widely used to support ceramic substrates in catalytic converters and behaves very much like hyper-foam material under compressive loading. Experiments show that compressive loading curves depend on the ram speed and the number of cycles. The unloading curves show different slopes and paths that depend less on the ram speed and number of cycles. The slopes of the unloading curves decrease as the plastic strain increases; this is referred to as “softening” in this study. The effects of rate, softening, and plastic deformation must be considered to model the mechanical response of intumescent mat material. Finite deformation theory is applied with a multiplicative decomposition of the deformation gradient tensor. The developed theory is implemented as an implicit finite element algorithm in ABAQUS^TM/STANDARD. The necessary material parameters are extracted from experiments. Numerical simulations show good agreement with experiments.