A modified Drucker-Prager Cap model for die compaction simulation of pharmaceutical powders

In this paper, we present a modified density-dependent Drucker-Prager Cap (DPC) model to simulate the compaction behaviour of pharmaceutical powders. In particular, a nonlinear elasticity law is proposed to describe the observed nonlinear unloading behaviour following compaction. To extract the material parameters for the modified DPC model, a novel experimental calibration procedure is used, based on uniaxial single-ended compaction tests using an instrumented cylindrical die. The model is implemented in ABAQUS by writing a user subroutine, and a calibration process on microcrystalline cellulose (MCC) Avicel PH101 powders is detailed. The calibrated parameters are used for the manufacturing process simulation of two kinds of typical pharmaceutical tablets: the flat-face tablet and the concave tablet with single or double radius curvatures. The model developed can describe not only the compression and decompression phases, but also the ejection phase. The model is validated by comparing finite element simulations with experimental loading–unloading curves during the manufacture of 8 and 11 mm round tablets with flat-face (FF), single radius concave (SRC) and double radius concave (DRC) profiles. Moreover, the density and stress distributions during tabletting are used to analyse and explain the failure mechanism of tablets. The results show that the proposed model can quantitatively reproduce the compaction behaviour of pharmaceutical powders and can be used to obtain the stress and density distributions during compression, decompression and ejection.     

基于颗粒物质力学的铁粉末压制中摩擦特性对力链演化影响

结合颗粒物质力学理论,通过离散元法实现铁粉末压制过程模拟并通过压制方程进行验证,针对粉末体系中的力链演化问题,提出力链特征定量分析方式,进一步通过分析不同颗粒间摩擦系数、侧壁摩擦系数与颗粒运动状态转变的方式,探讨摩擦特性对力链量化特征的影响,从而建立摩擦行为与力链演化间的联系. 研究结果表明:随颗粒间摩擦系数增大,整体力链数目变少,力链方向系数、承载不均匀度及单位屈曲度均变大,而随侧壁摩擦系数增大,力链特征差异较小,则颗粒间摩擦系数较侧壁摩擦系数对力链特征演化具有更显著影响. 同时发现,颗粒接触状态的改变与力链特征演化间具有对应性. 研究成果将进一步拓展粉末压制中考虑摩擦行为及力链演化过程在内的粉体致密化行为理论.      

Correlation mechanism of friction behavior and topological properties of the contact network during powder compaction

The effect of friction behavior on the compacted density is significant, but the relationship between the topological properties of the contact network and friction behavior during powder compaction remains unclear. Based on the discrete element method (DEM), a DEM model for die compaction was established, and the Hertz contact model was modified into an elastoplastic contact model that was more suitable for metal-powder compaction. The evolution of the topological properties of the contact network and its mechanism during powder compaction was explored using the elastoplastic contact model. The results demonstrate that the friction behavior between the particles is closely related to the topological properties of the contact network. Side wall friction results in smaller clustering coefficient (CC) and excess contact (EC) in the lower region near the side wall. Corresponding to this phenomenon, the upper region near the side wall has more high-stress particles when the major principal stress threshold was considered, and the CC and EC are significantly higher than those in the other regions. This study provides a theoretical basis for improving powder compaction behavior.     

Numerical simulation of density distribution during compaction of iron powders

Summary The compaction process of iron powder is considered. Due to negligible elastic strains the rigid-plastic model is applied. A yield condition containing the first stress invariant is used. All material functions depend on the relative density of the powder, which changes during the compaction process. Siebel friction law is applied, and the friction factor is considered to be depending on the relative density. Various material functions are applied in the numerical simulation, and the results are compared with experimentally obtained data. The best fitting material functions and friction factors are obtained. Accepted for publication 18 July 1996     

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.     

高速列车铁基烧结闸片材料的摩擦磨损性能研究

采用粉末冶金工艺,通过对材料组成和工艺等的实验研究,获得了一种铁基烧结闸片材料,对材料的物理机械性能、摩擦磨损性能和微观组织结构等进行了分析测试,探讨了烧结摩擦材料的摩擦磨损机理以及材料微观组织结构与摩擦磨损性能之间的关系。结果表明：该材料摩擦系数较高（0．31）,磨损率低（0．022mm/次）,摩擦稳定性优良;同时具有良好的物理机械性能,是一种潜在的高速列车制动闸片材料。烧结摩擦材料的摩擦机理归于啮合和粘着,而磨损机理归于磨粒磨损和疲劳裂纹萌生及扩展。     

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.     

Modeling of the metal powder compaction process using the cap model. Part I. Experimental material characterization and validation

In order to produce crack free metal powder compacts that respect both the dimensional tolerances and the mechanical strength requirements, both tooling design and compaction sequence have to be adequately determined. The finite element method, through the use of an appropriate constitutive model of the powder medium, has recently been used as an efficient design tool. The accuracy of this method highly depends on the faithfulness of the constitutive model and the quality of the material parameter set. Furthermore, in order for the simulation results to be reliable, they should be experimentally validated on real parts featuring density variations. Hence, the main concerns of this paper are the development of a standard calibration procedure for the cap material model as well as the development of a reliable technique for the experimental validation of the powder compaction simulation results.The developed calibration procedure, applied for the case of 316L stainless steel powders, is based on a series of isostatic, triaxial and uniaxial compaction tests as well as resonant frequency tests. In addition, a sensitivity study was performed in order to determine the relative importance of each factor and basic simulations served to validate the parameter set extraction procedure.On the other hand, a local density measurement technique was developed for the experimental validation of the model results. This technique is based on correlation with Vickers macro-hardness. Finally, an application featuring the compaction of a 316L stainless steel cylindrical component is presented to illustrate the predictive capabilities of the cap material model as well as the accuracy of the acquired material parameter set.     

The flow behavior of powder stearin-based methyl ester sulfonates and the effect of glidant

The preparation and behavior of powder stearin-based methyl ester sulfonates (MES) with the addition of builder as a glidant agent was studied. MES is an anionic surfactant and its performance is equivalent to petroleum-based linear alkylbenzene sulfonates (LAS), the workhorses of the detergent industry. At the same time, zeolites or soda ash were the alternative builders for non-phosphate-based detergent. The behavior of powder MES properties was measured in terms of morphology, particle size, cohesion, caking, and compaction. Before that, these palm stearin-based MES of carbon chain 16–18 with ratios of 98:2, 80:20, and 60:40 in flakes were ground using a high shear mixer by 23,000 rpm to produce powder particles. Decreasing the particle size of MES powder can reduce the powder's cohesion, caking, and compaction. The addition of zeolite or soda ash as a glidant in powdered MES can improve the caking behavior. The high stearic in MES greatly influenced getting fine particle powders and required more glidant agents. This powder MES with excellent powder characteristics can perform well as a bio-based cleaning product.     

The use of models in the study of stresses during soil compaction

In the present study, it is described the experimental method for measuring the direction and the magnitude of stresses during mechanical soil compaction. These stresses result in an increase in soil density. The greatest effect during the compaction results from developing a vertical component of stress in the soil. This component of stress can be measured experimentally. This stress is a function of many soil factors and the characteristics of the compaction machine. Considering the particular and, in many aspects, unknown processes of these effects on the compaction, the determination of soil compaction with models becomes very difficult. The system equation in the model is obtained by means of dimensional and numerical analysis using special computer programs.     

Problems of powder flow in tabletting processes

Summary The flow of non-compacted granules in the tablet machine hopper is discussed with relevance to the unit dose of drug, which is required to be dispensed. The various factors used to describe powder flow such as angle of repose, interparticulate cohesion and friction, flow through apertures, bulk density and die fillability are considered. The effects of humidity and of addition of fines or lubricants and the use of commercially available apparatus for induced die feeding are included.During compression powder flows to form a dense compact. Theories of this densification and the effects of entrapped air and die wall friction during the compression and ejection of the tablets are examined.An attempt is made to correlate non-uniformity in the final tablet with problems of powder flow.Paper presented at a meeting of the British Society of Rheology, University of Nottingham, April 6–8, 1965.     

非公度接触石墨烯层间摩擦对压入深度的依赖性

近年来,以石墨烯为代表的层状二维纳米材料的摩擦力学行为受到广泛关注,许多新的纳尺度摩擦现象、规律及机理被陆续报道,推动纳米摩擦学取得了重要进展.然而,由于纳米级摩擦十分复杂,在建立摩擦力与影响因素之间的直接关联方面依然进展非常缓慢.论文利用分子动力学模拟方法,研究了衬底支撑石墨烯基底与石墨烯滑片之间的摩擦行为,着力考察了非公度接触情况下的摩擦规律.结果表明,石墨烯滑片和基底之间的摩擦力与压入深度直接相关,说明压入深度可作为纳尺度摩擦力的重要度量指标.特别地,法向载荷和衬底刚度对石墨烯摩擦的影响,都可通过压入深度归一化处理.该结果对理解二维材料表面弹性影响的摩擦规律具有重要的理论意义.     

非公度接触石墨烯层间摩擦对压入深度的依赖性

近年来, 以石墨烯为代表的层状二维纳米材料的摩擦力学行为受到广泛关注, 许多新的纳尺度摩擦现象、规律及机理被陆续报道, 推动纳米摩擦学取得了重要进展. 然而, 由于纳米级摩擦十分复杂, 在建立摩擦力与影响因素之间的直接关联方面依然进展非常缓慢. 本文利用分子动力学模拟方法, 研究了衬底支撑石墨烯基底与石墨烯滑片之间的摩擦行为, 着力考察了非公度接触情况下的摩擦规律. 结果表明, 石墨烯滑片和基底之间的摩擦力与压入深度直接相关, 说明压入深度可作为纳尺度摩擦力的重要度量指标. 特别地, 法向载荷和衬底刚度对石墨烯摩擦的影响,都可通过压入深度归一化处理. 该结果对理解二维材料表面弹性影响的摩擦规律具有重要的理论意义.     

仿生叠层构型石墨烯对铝基复合材料的纳米摩擦性能的影响

利用纳米压痕和纳米划痕试验表征了仿生叠层构型铝基石墨烯复合材料(Bio-inspired laminated graphene reinforced aluminum martrix composite, BAMC)与纯铝的力学性能和摩擦磨损性能. 鉴于摩擦力由黏着作用和犁沟作用两分量共同组成,对比探究了BAMC与纯铝在微观摩擦磨损过程中的弹塑性转变过程,分析了黏着作用与犁沟作用在摩擦力中的贡献度,揭示了其微观摩擦磨损机制. 结果表明:相较于纯铝,BAMC的纳米硬度提高了约24%,总摩擦系数(Friction coefficient)降低了约28%,黏着作用分量和犁沟作用分量分别降低了32%和16%. 换言之,复合材料中的异质界面产生异质变形诱导强化,进而增强了应变硬化,使仿生叠层石墨烯铝基复合材料的硬度得到明显提升,并且仿生叠层构型的石墨烯主要通过降低黏着作用来实现减磨. 从微纳米尺度揭示了BAMC的力学性能和摩擦磨损性能显著提升的机理,可为提升其摩擦磨损性能提供理论依据. 目前的工作通过纳米划痕和纳米压痕强调了叠层结构石墨烯的添加对块体复合材料的摩擦性能的影响,并表明仿生叠层构型铝基石墨烯是搭建仿生叠层结构的小尺寸理想增强体.      

二维材料纳米尺度摩擦行为及其机制

二维材料是指厚度仅有单层或数层原子的晶体或非晶材料,其优异的物理、力学和化学性能给纳米尺度超薄固体润滑材料的设计和发展带来了新的契机.同时,二维材料独特而简单的拓扑结构也为深入了解摩擦的微观机制提供了一个理想的对象.论文综述了以石墨烯为主的二维材料纳米尺度摩擦和磨损研究的进展.根据相对运动形式的不同,分别介绍了二维材料的层间滑动和表面摩擦行为,并详细阐述了这些独特行为背后的微观物理机制;同时还重点介绍了若干种影响和调控二维材料表面摩擦性能的典型方法和策略,以及二维材料纳米尺度的磨损行为及其失效模式.最后,还对纳米尺度二维材料摩擦研究进行了小结,并展望了该领域尚待探索的若干研究方向.     

Dynamics analysis of 2-DOF complex planar mechanical system with joint clearance and flexible links

Joint clearance and flexible links are two important factors that affect the dynamic behaviors of planar mechanical system. Traditional dynamics studies of planar mechanism rarely take into account both influence of revolute clearance and flexible links, which results in lower accuracy. And many dynamics studies mainly focus on simple mechanism with clearance, the study of complex mechanism with clearance is a few. In order to study dynamic behaviors of two-degree-of-freedom (DOF) complex planar mechanical system more precisely, the dynamic analyses of the mechanical system with joint clearance and flexibility of links are studied in this work. Nonlinear dynamic model of the 2-DOF nine-bar mechanical system with revolute clearance and flexible links is built by Lagrange and finite element method (FEM). Normal and tangential force of the clearance joint is built by the Lankarani–Nikravesh and modified Coulomb’s friction models. The influences of clearance value and driving velocity of the crank on the dynamic behaviors are researched, including motion responses of slider, contact force, driving torques of cranks, penetration depth, shaft center trajectory, Phase diagram, Lyapunov exponents and Poincaré map of clearance joint and slider are both analyzed, respectively. Bifurcation diagrams under different clearance values and different driving velocities of cranks are also investigated. The results show that clearance joint and flexibility of links have a certain impact on dynamic behavior of mechanism, and flexible links can partly decrease dynamic response of the mechanical system with clearance relative to rigid mechanical system with clearance.     

钨粉爆炸烧结对粉末初始参数依赖关系的研究

本文从粉末爆炸烧结的能量沉积概念出发,提出了粉末爆炸烧结下限概念,讨论了钨粉末的爆炸烧结密度值和硬度分布对粉末初始参数的依赖关系,给出了实验结果。从理论和实验阐述了粉末初始参数在爆炸烧结实验中的重要作用。     

The biaxial loading response of powder aluminum at elevated temperature

Nuclear fuel can be fabricated using powder-metallurgy processes by compacting uranium-oxide powder with aluminum powder to form a cermet and then extruding the cermet to form fuel tubes. This method of production allows greater control of uranium-oxide particle size and distribution in the tube, making the production of fuel with greater concentrations of uranium oxide possible, and thus decreasing the volume of radioactive waste remaining after the fuel is spent. As the concentration of uranium oxide increases, however, there is an increase in failures during extrusion. To address this problem, an experimental procedure was developed to examine the response of powder aluminum, a material with a structure similar to that of the cermet fuel, to biaxial loadings such as those experienced during extrusion. Biaxial loadings can be varied from pure shear to simple tension or compression, or to combinations of these loadings in a numerically controlled ‘tension-torsion’ testing machine. Data obtained using this system were used to develop a model for the post-yield behavior in extruded powder aluminum which includes information derived both from the macroscopic stress-strain behavior of 1100 aluminum and extruded powder aluminum and from the observed microscopic structure of the extruded powder aluminum. This paper describes the development of the experimental system and shows the different biaxial mechanical behavior of the two materials. Test fixtures were developed and software was written to control constant strain-rate tension, compression, torsion, combined tension-torsion, and combined compression-torsion tests performed using a computer-controlled MTS biaxial testing machine. Extruded powder aluminum and 1100 aluminum specimens were tested at 427°C, the powder-aluminum extrusion temperature, under those loading conditions. Each specimen was subjected to only one loading cycle. Data were recorded during loading only. Tested specimens were also sectioned and examined microscopically.     

一种预测颗粒增强复合材料界面力学性能的新方法

界面在颗粒增强复合材料中起到传递载荷的关键作用,界面性能对复合材料整体力学行为产生重要影响.然而由于复合材料内部结构较为复杂,颗粒与基体间的界面强度和界面断裂韧性难以确定,尤其是法向与切向界面强度的分别预测缺乏有效方法.本文以氧化锆颗粒增强聚二甲基硅氧烷(PDMS)复合材料为研究对象,提出一种预测颗粒增强复合材料界面力...