Approach the powder contact force,voidage, tensile stress,wall frictional stress and state diagram of powder bed by simple pressure drop monitoring

The evaluation of the mechanical properties and the state of a powder bed are essential for industrial powder operations. We assume that the bed incipient yield is approximately the bed incipient fluidization, and the particle contact force, the bed voidage, the bed tensile stress and the bed-wall frictional stress can be determined by simple pressure drop monitoring when gradually increasing the superficial gas velocity from zero. A two-dimensional powder bed voidage-tensile stress state diagram at zero shear stress under anisotropic consolidation is initially prepared. For the sample powder bed, we show that the isotropic tensile stress estimated by the powder yield locus extrapolation, 340 Pa−770 Pa, from a shear tester is different from the anisotropic tensile stress evaluated, 120 Pa–180 Pa, by the pressure drop overshoot approximation.     

Analysis of constant-volume shear tests based on precise measurement of stresses in powder beds

This study demonstrates a new constant-volume shear test configuration to analyze the stresses in powder beds and evaluate powder flowability. A novel cylindrical shear cell geometry and load cell arrangement allowed precise measurement of the normal stress acting on the shear planes of the powder beds. The stress transmission ratio between the top and shear planes decreased with increasing ratio of the powder bed height in the upper section of the shear cell to the shear cell diameter. This was due to friction between the powder bed and the side wall of the upper section of the shear cell. Using the measured values of the normal stress on the shear planes, the effects of the powder bed height and shear cell diameter were eliminated from the data. In addition, to evaluate the shear properties of the powder beds, the powder yield locus, consolidation yield locus, critical state line, shear cohesion, and void fraction were obtained from a single shear test. The powder yield locus data were used to obtain flow functions.     

Characterization of polymeric structural foams under compressive impact loading by means of energy-absorption diagram

The mechanical properties at room temperature of three polymeric foams (namely EPP, PUR and PS/PA foams) have been experimentally evaluated in both static and impact loading conditions. The energy absorption characteristics have been examined both through the energy-absorption diagram method and through the efficiency diagram method. The meaning of the efficiency parameter, already used in the literature, has been explained in a proper, satisfactory way. It is shown that the maximum of the efficiency identifies the condition for optimal energy absorption of the foam, while the maximum stress reaches a value limited through other design considerations. The efficiency diagram method is then used to obtain synthetic diagrams useful to characterize the material and to help the design of energy absorbing components. These synthetic selection diagrams are obtained for the three tested materials. Finally, some consideration are drawn comparing the mechanical performance of the three considered types of foams and their dependency on density.     

The Prediction of the Emissivity and Thermal Conductivity of Powder Beds

A simple model for estimating the emissivity of the surface of a powder bed by knowing only the bed porosity and its solid emissivity is presented. Estimates by the model are compared with experimental measurements for powder beds of alumina, silicon carbide, and iron. Agreement within the uncertainty of the measurements of±10% is obtained. A view factor that adopts the predicted emissivity of the powder beds into its term is suggested for the calculation of the conductivity by radiation. For the prediction of the thermal conductivity of the powder beds, the authors compared the existing models in literature. They rederived the Zehner-Schlunder equation (1970) and made some modifications to it. Comparison of predictions by this equation with 424 measured values shows the predictions to be accurate to within a ±30% relative error.     

Development of a reduced-order model for large-scale Eulerian–Lagrangian simulations

Multiphase flows with solid particles are commonly encountered in various industries. The CFD–DEM method is extensively used to simulate their dynamical behavior. However, the application of the CFD–DEM method to simulate industrial-scale powder processes unavoidably leads to huge computational costs. With the aim of overcoming this issue, we propose a nonintrusive reduced-order model for Eulerian–Lagrangian simulations (ROM-EL) to efficiently reproduce gas–solid flow in fluidized beds. In the model, a Lanczos based proper orthogonal decomposition (LPOD) is newly employed to efficiently generate a set of POD bases. After the numerical snapshots are projected onto the reduced space spanned by the POD bases, a series of multidimensional functions of POD coefficients are constructed using a surrogate interpolation method. To demonstrate the effectiveness of this model, validation studies are performed based on the simulations of a fluidized bed. The macroscopic properties, such as the particle distribution, bed height, pressure drop, and distribution of bubble size, are shown to agree well in the CFD–DEM model and ROM-EL. Further, our proposed ROM-EL reduces the computational cost by several orders of magnitude compared with the CFD–DEM simulation. Accordingly, the ROM-EL could significantly contribute to the progress of modeling and simulation for industrial granular flows.     

A mathematical framework of high-order surface stresses in three-dimensional configurations

The mathematical behavior of a curved interface between two different solid phases with surface or interface stress effects is often described by the generalized Young–Laplace (YL) equations. The generalized YL equations can be derived by considering force equilibrium of a thin interphase with membrane stresses along the interface. In this work, we present a refined mathematical framework by incorporating high-order surface or interface stresses between two neighboring media in three dimensions. The high-order interface stresses are resulting from the nonuniform surface stress across the layer thickness, and thereby effectively inducing a bending effect. In the formulation, the deformation of the thin interphase is approximated by the Kirchhoff–Love assumption of thin shell. The stress equilibrium conditions are fulfilled by consideration of balance for forces as well as stress couples. By simple geometric expositions, we derive in explicit form the stress jump conditions for high-order surface stresses. In illustrations, the bending deformation of nanoplates with high-order stresses is investigated and is compared with the results by the conventional YL equation.     

Evaluation of mechanical properties of nanoparticles using a constant-volume shear tester

Nanoparticles have advantageous small-size and surface effects that impart them with unique mechanical properties. To evaluate these properties, a constant-volume shear tester that can precisely measure stresses on the shear plane was used. Six samples, namely, hydrophilic and hydrophobic silica, alumina, and titania nanoparticles, were prepared for the shear tests. For each sample, a single shear test provided the void fraction, stress relaxation ratio, stress transmission ratio, powder yield locus, consolidation yield locus, critical state line, shear cohesion, and flow function. All the tests were conducted under ambient conditions using powder beds, in which the void fractions were in the range of 0.89–0.96. A series of analyses demonstrated that the hydrophilic nanoparticles have lower flowability than the hydrophobic nanoparticles, indicating that moisture on the surface increases the cohesion and inhibits the flow.     

A theory of the molecular-mass dependence of glass transition temperatures for polydisperse homopolymers

Arbitrary distributions of finite molecular-mass homopolymers are treated as one-phase solutions of chain ends and high polymers in order to derive an entropie relation for the dependence of their glass transition temperatures on the number-average degree of polymerization. Absolute predictions of this equation from high molecular-mass and dimer properties are found to be in good agreement with dilatometric transition temperatures for polystyrene. The theoretical equation is generalized to allow for the characterization of chain ends by properties other than those of dimers. An initial approximation to the entropic expression is obtained by neglect of the difference between chain-end and high-polymer transition increments of heat capacity. Two subsequent approximations arise from a series expansion of logarithmic functions. In order of decreasing accuracy these three approximations are: a new form of the Ueberreiter-Kanig equation, a logarithmic expression, and a new form of the Fox-Flory relation.     

Mechanical properties of titanium-based Ti–6Al–4V alloys manufactured by powder bed additive manufacture

Additive manufacturing is currently a topic of considerable interest at both academic and industrial levels. While a significant amount of data exists on the mechanical properties and structure–property relationships of traditional wrought alloys, less information is available on alloys manufactured by additive manufacture. This review examines current state-of-the-art manufacture of titanium-based Ti–6Al–4V alloys by powder bed additive manufacture. Published mechanical properties to date are collected which include tensile strength, yield strength, hardness, wear, fracture toughness and fatigue. Differences in microstructure and properties compared to conventional wrought alloys of the same composition are described.     

Modelling of materials properties in duplex stainless steels

Abstract

Work is being undertaken to develop a new multiplatform software programme for predicting a wide range of materials properties for various alloy types. These properties include thermophysical and physical properties, mechanical properties, time–temperature transformation (TTT)/continuous cooling transformation diagrams etc. and the calculations are being applied to a variety of multicomponent alloy types, such as Ni based superalloys, steels, Ti alloys, Al alloys. The current paper concentrates on duplex stainless steels and describes the scientific background used for the calculation of TTT diagrams and mechanical properties for these materials. It is shown that there is very good agreement between the calculated TTT diagrams and the observed results from the literature for the formation of the σ, χ, and the chromium rich α' phase, while the calculated proof stress, tensile stress and hardness are in good agreement with the available experimental data. The effects of solution treatment temperature and the volume fraction of σ phase on mechanical properties are also discussed.     

Viscosity and separation performance of a gas-solid separation fluidized beds

A theoretical model of viscosity in gas-solid separation fluidized beds is established according to the two-phase flow theory of fluidized beds. After comparing theoretical and measured values, the correlation coefficient between the two is as high as 0.99, showing that the model has good predictability for the viscosity of fluidized beds. Meanwhile, the viscosity and its influencing factors were studied using a Brookfield viscometer. The study shows that smaller medium particles (0.074–0.15?mm) can reduce the viscosity of fluidized beds, but they will aggravate the viscosity fluctuation at more than 5?wt% addition, which is unfavorable to the stability of fluidized beds. In addition, in the actual separation process, the external factors (such as moisture and coal powder content) also affect the viscosity of the fluidized beds. Increasing the moisture increases the viscosity of the fluidized bed, whereas coal dust has the opposite effect. In order to ensure the stability of the fluidized bed, the bed moisture content should be controlled below 1?wt%, while the content of coal powder should be limited below 5?wt%. Based on separation tests, reducing the viscosity will improve the separation performance of a fluidized bed at the proper fluidized gas velocity, with the lowest possible error E_p of 0.085.     

A new approach to the positive mean stress diagram in mechanical design

The Gerber, modified Goodman, Soderberg, Bagci, ASME‐elliptic and Clemson diagrams are proposed for estimating mechanical element fatigue strength under positive mean and alternating stresses. However, all of these diagrams are either conservative or have fields containing stress greater than yield strength of mechanical element materials. The aim of this study was to propose a new simple diagram with an exponential power k for various types of mechanical element materials. Exponential power k values of steel and Al‐alloy materials were about 0.80 and 0.45, respectively. The proposed diagram (Sekercioglu line) had a minimum average absolute deviation (X_m) of 8.56 %, lower than the Bagci, ASME‐elliptic and Clemson diagrams. The Sekercioglu line can be successfully used in fatigue design processes because of its simple structure and its less conservative nature.     

Solid Flow Transition in Liquid and Three-Phase Fluidized Beds

Flow transition of solids in liquid and three phase fluidized beds of Newtonian and non-Newtonian fluids have been studied in a 15.2 cm-ID pyrex glass column. The relation between the fluid flow rate and the bed porosity in three phase fluidized beds have been determined in terms of effective volumetric flux of fluid phases from the modification of the Richardson and Zaki's equation. The modified particle Reynolds Number exhibited its maximum value with the variation of bed porosity in liquid and three phase fluidized beds. The drag coefficient changed its slope apparently at the bed porosity where the maximum value of the modified particle Reynolds number could be attained. At the flow transition condition, the continuity wave velocity, energy dissipation rate, and the continuity shock wave velocity found to have their maximum values. Also, the immersed heater-to-bed and wall-to-bed heat transfer coefficients, wall-to-bed mass transfer coefficient, liquid radial mixing coefficient and solid particle diffusivity in the literature data were found to have maximum values at the transition condition of liquid and three phase fluidized beds.     

A new method for evaluating powder flowability using constant-volume shear tester,

This is an article translated from the original version published in the Journal of the Society of Powder Technology, Japan. A new method for evaluating powder flowability is developed using a constant-volume shear tester; this tester measures the upper and lower normal stresses and the shear stress acting on a powder bed. A single shear test provides a series of characteristics, such as the powder yield locus (PYL), consolidation yield locus (CYL), critical state line (CSL), shear cohesion, stress relaxation ratio, stress transmission ratio, and void fraction. The values of shear stress as a function of the normal stress and void fraction are visualized in three-dimensional diagrams. Furthermore, powder flowability is evaluated using a flow function obtained from the PYL.     

Numerical calculations of residual–stress relaxation in quenched plates

Abstract

Methods of thermal stress relief such as stretching and compression are compared for different thermal and mechanical properties during quenching. The heat equation for a simple geometric model, such as an infinite plate, is solved with an experimental surface conductance and a step–by–step method of determining the temperature field in the thickness of the plate. This field is introduced as data for the uncoupled thermal elastic–plastic model for quenching. In the calculation of the plastic–strain path, the thermal and mechanical properties are considered as temperature dependent for a homogeneous and isotropic material. Good agreement is found between the calculated residual stresses and experimental values for an aluminium alloy and a stainless steel. The predicted residual–stress distributions and strain history are then used as data for the numerical simulation of stress–relief methods with an incremental integration of the Prandtl–Reuss equation. This analysis allows the observation of the effects of small variations in mechanical properties during quenching on the residual–stress field after mechanical stress relief and the theoretical comparison of different processes.

MST/6     

Influence of Two-Step Heat Treatments on Microstructure and Mechanical Properties of a β-Solidifying Titanium Aluminide Alloy Fabricated via Electron Beam Powder Bed Fusion

Additive manufacturing technologies, particularly electron beam powder bed fusion (PBF-EB/M), are becoming increasingly important for the processing of intermetallic titanium aluminides. This study presents the effects of hot isostatic pressing (HIP) and subsequent two-step heat treatments on the microstructure and mechanical properties of the TNM-B1 alloy (Ti–43.5Al–4Nb–1Mo–0.1B) fabricated via PBF-EB/M. Adequate solution heat treatment temperatures allow the adjustment of fully lamellar (FL) and nearly lamellar (NL-β) microstructures. The specimens are characterized by optical microscopy and scanning electron microscopy (SEM), X-ray computed tomography (CT), X-ray diffraction (XRD), and electron backscatter diffraction (EBSD). The mechanical properties at ambient temperatures are evaluated via tensile testing and subsequent fractography. While lack-of-fusion defects are the main causes of failure in the as-built condition, the mechanical properties in the heat-treated conditions are predominantly controlled by the microstructure. The highest ultimate tensile strength is achieved after HIP due to the elimination of lack-of-fusion defects. The results reveal challenges originating from the PBF-EB/M process, for example, local variations in chemical composition due to aluminum evaporation, which in turn affect the microstructures after heat treatment. For designing suitable heat treatment strategies, particular attention should therefore be paid to the microstructural characteristics associated with additive manufacturing.     

车辆通过连续减速带时的非线性振动特性分析

在7自由度线性系统的基础上考虑悬架弹簧、阻尼和轮胎的非线性,以高速路段的连续减速带作为整车激励,通过对力学模型进行分析并运用拉格朗日法建立系统微分方程。通过MATLAB仿真软件对整车7自由度非线性振动模型的微分方程进行仿真,得到阻尼非线性系数和激励频率的分岔图,发现在一定区域内系统出现复杂的非线性振动,并通过时间历程图、相位图、Poincare截面图和PSP峰值图深入研究系统的周期、拟周期和混沌运动,揭示出阻尼非线性系数和激励频率对系统振动的影响,最后通过拟合即时速度从变速的角度揭示减速车辆通过连续减速带时的振动情况。     

Solid Flow Transition in Liquid and Three-Phase Fluidized Beds

ABSTRACT

Flow transition of solids in liquid and three phase fluidized beds of Newtonian and non-Newtonian fluids have been studied in a 15.2 cm-ID pyrex glass column. The relation between the fluid flow rate and the bed porosity in three phase fluidized beds have been determined in terms of effective volumetric flux of fluid phases from the modification of the Richardson and Zaki's equation. The modified particle Reynolds Number exhibited its maximum value with the variation of bed porosity in liquid and three phase fluidized beds. The drag coefficient changed its slope apparently at the bed porosity where the maximum value of the modified particle Reynolds number could be attained. At the flow transition condition, the continuity wave velocity, energy dissipation rate, and the continuity shock wave velocity found to have their maximum values. Also, the immersed heater-to-bed and wall-to-bed heat transfer coefficients, wall-to-bed mass transfer coefficient, liquid radial mixing coefficient and solid particle diffusivity in the literature data were found to have maximum values at the transition condition of liquid and three phase fluidized beds.     

Porous polytetrafluoroethylene film

The properties of porous films obtained by sintering a layer of polytetrafluoroethylene (PTFE) powder deposited onto a substrate were studied. The PTFE film porosity was controlled within 50–60% and the maximum pore size was 1–3 μm. The breaking stress of the films reached ～6 MPa at a 100% relative elongation. The influence of the particle size distribution function of the initial PTFE powder on the mechanical properties of sintered films is analyzed.     

Investigation of the possibility of reconstructing strain diagrams using the neural network approach

The results of neural network computational-experimental estimations of the strength properties of steels based on the diagrams of surface local elastoplastic deformation are given. The presented neural network approach to conversion of the indentation diagram into the diagram of uniaxial tension makes it possible to unify the specimen-free technique of determining the main mechanical properties of the materials of equipment. Neural network models for constructing point and interval estimates for different levels of elastoplastic deformation are described.