温压成型和微波烧结TiC/316L 复合材料的摩擦磨损特性

为提高TiC/316L不锈钢复合材料的致密度和力学性能,采用温压成型和微波烧结复合方法制备了质量百分数为5%的TiC/316L复合材料.在MM-200型环块磨损试验机上研究了复合材料在干摩擦条件下的摩擦磨损性能,并与传统粉末冶金法制备的复合材料耐磨性能进行了对比研究.结果表明:与传统粉末冶金法相比,在相同的烧结温度下,采用温压成型和微波烧结制备的TiC/316L复合材料虽然内部也存在一些孔隙,但组织比较均匀,烧结比较充分,复合材料的致密度和耐磨性均得以提高.随着温压压制压力的增加,复合材料的相对密度和耐磨性快速增加,但过高的压制压力不利于耐磨性的提高.摩擦磨损试验结果表明在压制压力为400 MPa时,复合材料的耐磨性较好.     

Numerical investigation into the influence of the punch shape on the mechanical behavior of pharmaceutical powders during compaction

During the production of pharmaceutical tablets using powder compaction, certain common problems can occur, such as sticking, tearing, cutting, and lamination. In the past, the compressibility of the powder was calculated only along the axis of the device; consequently, critical areas of the material throughout the volume could not be identified. Therefore, finite element method （FEM） can be used to predict these defects in conjunction with the use of an appropriate constitutive model. This article summarizes the current research in the field of powder compaction, describes the Drucker-Prager Cap model calibration procedure and its implementation in FEM, and also examines the mechanical behavior of powder during compaction. In addition, the mechanical behavior of pharmaceutical powders in relation to changes in friction at the wall of the system is examined, and the dependence of lubrication effect on the geometry of the compaction space is also investigated. The influence of friction on the compaction process for the flat-face, fiat-face radius edge, and standard convex tablets is examined while highlighting how the effects of friction change depending on the shape of these tablets.     

Extended finite element method in plasticity forming of powder compaction with contact friction

In this paper, a new computational technique is presented based on the eXtended Finite Element Method (X-FEM) in pressure-sensitive plasticity of powder compaction considering frictional contact. In X-FEM, the need for mesh adaption to discontinuity interface is neglected and the process is accomplished by partitioning the domain with some triangular sub-elements whose Gauss points are used for integration of the domain of the elements. The technique is applied by employing additional functions, which are added to approximate the displacement field of the elements located on the interface. The double-surface cap plasticity model is employed within the X-FEM framework in numerical simulation of powder material. The plasticity model includes a failure surface and an elliptical cap, which closes the open space between the failure surface and hydrostatic axis. The moving cap expands in the stress space according to a specified hardening rule. The frictional behavior of contact between two bodies is modeled by using the X-FEM technique and applying the Heaviside enrichment function. The application of X-FEM technique in simulation of pressure-sensitive material is presented in an incremental manner and the role of sub-elements in simulation of contact treatment is demonstrated. Finally, several numerical examples are analyzed with special reference to plasticity forming of powder compaction.     

Identification of material parameters for inelastic constitutive models: statistical analysis and design of experiments

In this paper we introduce stochastic methods to describe the influence of scattering test data on the identification of material parameters. We employ the viscoplastic constitutive model of Chan, Bodner, and Lindholm in its uniaxial form. The available test data result from three types of experiments performed at 600 °C on AINSI SS316 stainless steel, namely creep tests, constant strain rate tension tests with intermediate relaxation, and cyclic tension–compression tests. Each test has been performed with 12 specimens at different strain rates and stress rates respectively. However, for a serious statistical evaluation a larger number of experiments is required. In order to increase the number of tests we introduce stochastic simulations based on time series analysis which generate artificial data with the same stochastic behaviour as the experimental data. The method of stochastic simulation presents a widely accepted technique in engineering which does not add complexity to the process of parameter identification, but allows an investigation of the confidence in the fits of the material parameters. To keep the computation time for the identification of the material parameters as low as possible, very efficient numerical methods have to be implemented. The methods applied here for integration and nonlinear optimization are briefly introduced. The optimization strategy contains stochastic elements. Furthermore, we apply the method of statistical design of experiments to derive which combination of tests yields the most important information for an effective identification of material parameters.     

对316L不锈钢的非比例循环粘塑性本构描述

对循环硬化的３１６Ｌ不锈钢提出了一个考虑非比例循环加载下流动和硬化特性的粘塑性本构模型。模型中，通过随动硬化的背应力演化以各向同性阻力演化非比例循环路径及其历史的依赖关系来表征材料的非比例循环附加硬化和非比例循环流动特性，将模型用于预测３１６Ｌ不锈钢的圆形，正菱形应变路径的复杂循环变形行为，其预言结果与实验结果吻合很好。     

A nonclassical constitutive model for crystal plasticity and its application

I.IntroductionTheresearchoncrystalplasticitycanbedatedbackto1930'sill.AherHill[=],HillandRicely]builtupaperfectsystemofthegeometryandkineticsofCrystalplasticity,itsapplicatiollbecolllesmoreandmoreattractive,especiallyintheallalysisofpolycrystallinelllaterialssubjectedtoInultiaxiallynonproportionalcyclicloading.Ithasalreadybeenrealizedthattileillll,ol'talltforthepracticalapplicationis:tofindal.ealisticalldeasilyapplicableof'ystallineconstitutiverelationandaneffectivenumericalapproach.Tilecon…     

Inelastic analysis of new thermal ratchetting due to a moving temperature front

Results of the joint project by the Working Group of Inelastic Analysis, Committee on High Temperature Strength, Society of Materials Science, Japan, are summarized. The purpose of this project, consisting of two parts, is to find out an appropriate inelastic constitutive equation which can simulate the new thermal ratchetting of a cylinder subjected to a traveling axial temperature distribution. In the first part of this project, uniaxial strain and stress-controlled ratchetting behavior is simulated by plural constitutive equations in order to examine the ability to reproduce basic deformation behavior of 316FR stainless steel at room temperature and 650 °C. In the second part, inelastic analyses of the thermal ratchetting of a cylinder due to a traveling temperature distribution are performed. Experimental data of ten specimens made of SUS 316 and 316FR stainless steels are prepared for evaluating the following items: traveling distance, stress level and hold time at high temperature. A comparison between experiments and corresponding inelastic analyses using eight types of constitutive models is made, and the selection of the appropriate constitutive equation is discussed.     

Influence of non-proportional loading on ratcheting responses and simulations by two recent cyclic plasticity models

Aubin and her coworkers conducted a unique set of experiments demonstrating the influence of loading non-proportionality on ratcheting responses of duplex stainless steel. In order to further explore their new observation, a set of experiments was conducted on stainless steel (SS) 304L under various biaxial stress-controlled non-proportional histories. This new set of data reiterated Aubin and her coworkers’ observation and illustrated many new responses critical to model development and validation. Two recent and different classes of cyclic plasticity models, the modified Chaboche model proposed by Bari and Hassan and the version of the multi-mechanism model proposed by Taleb and Cailletaud, are evaluated in terms of their simulations of the SS304L non-proportional ratcheting responses. A modeling scheme for non-proportional ratcheting responses using the kinematic hardening rule parameters in addition to the conventionally used isotropic hardening rule parameter (yield surface size change) in the modified Chaboche model is evaluated. Strengths and weaknesses of the models in simulating the non-proportional ratcheting responses are identified. Further improvements of these models needed for improving the non-proportional ratcheting simulations are suggested in the paper.     

A new computational algorithm for contact friction modeling of large plastic deformation in powder compaction processes

In this paper, the large deformation frictional contact of powder forming process is modeled based on a new computational algorithm by imposing the contact constraints and modifying the contact properties of frictional slip. A simple and efficient numerical algorithm is presented for imposing the contact constraints and frictional contact properties based on the node-to-surface contact technique to simulate the large deformation contact problem in the compaction process of powder. The Coulomb friction law is used to simulate the friction between the rigid punch and the workpiece by the use of penalty approach. A double-surface cap plasticity model is employed together with the nonlinear contact friction algorithm within the framework of large FE deformation in order to predict the non-uniform relative density distribution during large deformation of powder die-pressing. Finally, the numerical schemes are examined for accuracy and efficiency in modeling of a set of powder components.     

A finite strain constitutive model for metal powder compaction using a unique and convex single surface yield function

Constitutive modelling of metal powder compaction processes is a challenge in view of realistic simulations. To this end, the article under consideration has two objectives: the first goal is to present a new unique and convex single surface yield function for pressure dependent materials, which is also applicable to other areas of granular materials such as soils or concrete. The flexibility is shown at various materials. The yield function is based on a log-interpolation of two known simple yield functions. A convexity proof of the new yield function is provided. The second objective is to propose a new rate-independent finite strain plasticity model for metal powder compaction, which is based on the multiplicative decomposition of the deformation gradient into an elastic and a plastic part with evolution equations for internal variables representing the basic behaviour of powder materials under compaction conditions. These variables are used for the evolution of the yield function in order to represent the compressible hardening behaviour of powder materials. On the basis of the constitutive model, the material parameters are identified at experimental data of copper powder.     

Constitutive equations for metal powders: application to powder forming processes

A new constitutive model for cold compaction of metal powders is developed. The plastic flow of metal powders at the macroscopic level is assumed to be representable as a combination of a distortion mechanism, and a consolidation mechanism. For the distortion mechanism the model employs a pressure-sensitive, Mohr–Coulomb type yield condition, and a new physically based non-associated flow rule. For the consolidation mechanism the model employs a smooth yield function which has a quarter-elliptical shape in the mean-normal pressure and the equivalent shear stress plane, together with an associated flow rule. The constitutive model has been implemented in a finite element program. The material parameters in the constitutive model have been calibrated for MH-100 iron powder by fitting the model to reproduce data from true triaxial compression experiments, torsion ring-shear experiments, and simple compression experiments. The predictive capability of the constitutive model and computational procedure is checked by simulating two simple powder forming processes: (i) a uniaxial strain compression of a cylindrical sample, and (ii) forming of a conical shaped-charge liner. In both cases the predicted load–displacement curves and density variations in the compacted specimens are shown to compare well with corresponding experimental measurements.     

考虑塑性应变记忆恢复的循环棘轮本构模型研究

在统一粘塑性循环本构理论框架下,以Ohno-Abdel-Karim非线性随动硬化模型为基础,建立了一个循环本构模型。模型通过引入塑性应变幅值记忆效应,并在塑性应变记忆项中加入恢复系数,提高了对循环硬化材料单轴棘轮行为的预言能力。将模型应用于316L不锈钢单轴棘轮行为的描述中,模拟不同平均应力、应力幅值下的棘轮应变,均与实验数据吻合较好,证明本文改进的本构模型能合理地描述循环硬化材料的单轴棘轮行为。     

Computational simulation of the dependence of the austenitic grain size on the deformation behavior of TRIP steels

Due to the strain-induced martensitic transformation which occurs during plastic deformation, a transformation-induced plasticity (TRIP) phenomenon is generated. With the TRIP phenomenon, the TRIP steel possesses favorable mechanical properties such as high strength, ductility and toughness, and is frequently employed as a structural material. In the past, several researchers clarified experimentally that the strain-induced martensitic transformation and the deformation behavior of TRIP steel depend upon the austenitic grain size. In order to obtain the expected mechanical properties of TRIP steel through control of the austenitic grain size, prediction and control of the material characteristics in the deformation processes is essential. Here, the new strain-induced martensitic transformation kinetics model and constitutive equation of TRIP steels are proposed by considering the dependence of the austenitic grain size. Then, the deformation behavior of a type 304 austenitic stainless steel cylinder is simulated under different environmental temperatures with the various austenitic grain sizes by the finite-element method along with newly-proposed constitutive equations. Finally, the validity of proposed constitutive equations and the possibility of the improvement of the mechanical properties through control of the austenitic grain size are discussed.     

转动惯量法在多轴疲劳本构关系预测中的应用

一些金属材料在承担多轴非比例加载过程时,会产生额外非比例附加强化或软化现象,这一现象往往会导致在评估疲劳寿命时因为材料本构关系的不确定而引起预测结果出现较大误差．因此基于单轴疲劳理论得出的寿命预测模型并不能准确地预测多轴非比例疲劳加载下的材料寿命．针对此问题,本文阐述了非比例附加强化效应产生的原因及结果,结合转动惯量法的理论和塑性增量法,建立了预测多轴低周疲劳加载下循环应力-应变曲线的数值计算模型．利用316L 不锈钢试样在5 种加载路径下的实验数据对预测结果进行了验证,结果表明该模型具有良好的预测有效性及精度．     

高分子材料机械密封磨损特性及表面织构的影响

为提高金属/高分子材料机械密封的抗磨损性能,采用光刻-电解技术在316不锈钢表面制作微凹坑阵列形式的表面织构,与5种不同弹性模量的高分子材料组成摩擦副进行磨损试验.试验结果表明,对弹性模量最小的UHMWPE材料,表面织构起到了增磨作用,对其他四种弹性模量较高的材料,表面织构起到减磨作用,而且,随着高分子材料弹性模量的增大,表面织构表现出的减磨作用也随之增大.为解释这个现象,利用ANSYS有限元分析软件对摩擦副接触面进行了应力和变形分析,结果表明:织构化表面在接触过程中会产生应力集中和表面形变,材料的弹性模量越小,凹坑引起的变形越明显,可能产生的切削作用越显著.     

Inverse approach to identification of material parameters of cyclic elasto-plasticity for component layers of a bimetallic sheet

The present paper proposes a novel approach to the identification of the mechanical properties of individual component layers of a bimetallic sheet. In this approach, a set of material parameters in a constitutive model of cyclic elasto-plasticity are identified for the two layers of the sheet simultaneously by minimizing the difference between the experimental results and the corresponding results of numerical simulation. This method has an advantage of using the experimental data (tensile load vs strain curve in the uniaxial tension test and the bending moment vs curvature diagram in the cyclic bending test) for a whole bimetallic sheet but not for individual component layers. An optimization technique based on the iterative multipoint approximation concept is used for the identification of the material parameters. This paper describes the experimentation, the fundamentals and the technique of the identification, and the verification of this approach using two types of constitutive models (the Chaboche-Rousselier and the Prager models) for an aluminum clad stainless steel sheet.     

A general cyclic plasticity model taking into account yield surface distortion for multiaxial ratchetting

Most of the theoretical studies devoted to multiaxial ratchetting are focused on the location of the macroscopic yield domain in order to predict the correct direction of plastic strain rate, since normality of the plastic strain rate to the yield surface is usually assumed. To the authors' knowledge, the shape of subsequent yield surfaces was always kept constant in these models for simplicity reasons but unlike experimental observations. In a previous paper [J. Eng. Mater. Technol. 124(4) (2002) 402], the authors have explained the need to take into account yield surface distortion in macroscopic modeling and have therefore proposed such a constitutive model but only for biaxial loadings. In the present paper, the generalization of this distortional model is proposed for any loading paths. The model is then identified and validated on a large data base obtained firstly with an efficient polycrystalline model that can predict multiaxial ratchetting as well as yield surface distortion, and secondly with the experimental results of complex tests realized on a type 316L stainless steel.     

Numerical simulation of laser ultrasonic detection of the surface microdefects on laser powder bed fusion additive manufactured 316L stainless steel

A numerical model is presented in this article to investigate the interactions between laser generated ultrasonic and the microdefects (0.01 to 0.1 mm), which are on the surface of the laser powder bed fusion additive manufactured 316L stainless steel. Firstly, the influence of the transient sound field and detection positions on Rayleigh wave signals are investigated. The interactions between the varied microdefects and the laser ultrasonic are studied. It is shown that arrival time of reflected Rayleigh (RR) waves wave is only related to the location of defects. The depth can be checked from the feature point Q, the displacement amplitude and time delay of converted transverse (RS) wave, while the width information can be evaluated from the RS wave time delay. With the aid of fitting curves, it is found to be linearly related. This simulation study provides a theoretical basis for quantitative detection of surface microdefects of additive manufactured 316L stainless steel components.     

Experiments and Material Parameter Identification Using Finite Elements. Uniaxial Tests and Validation Using Instrumented Indentation Tests

In this article, we focus our attention on the relation between instrumented indentation tests and the prediction by means of finite element calculations. To this end, a finite strain viscoplasticity model of Perzyna-type with non-linear isotropic and kinematic hardening is calibrated at experimental data of steel S690QL. A particular concept for conducting uniaxial tensile and compression tests is taken up in order to represent the basic rate-dependent material behavior. In this respect, an algorithmic framework of material parameter identification using finite elements is proposed leading to a two-stage procedure in the case of the underlying rate-dependent constitutive model. On the basis of the termination points of relaxation the rate-independent equilibrium stress state can be identified and all viscous parts of the model are obtained using rate-dependent loading paths. Finally, use is made of finite elements for predicting indentation experiments, which results in a critical view on modeling and parameter identification on the basis of experimental results occurring in instrumented indentation tests.