PRODUCT ENGINEERING OF PARTICULATE SOLIDS

An important development in Particle Technology is directed towards tailored product properties, i.e. product engineering. Product properties are strongly related to the disperse properties of the particles, i.e. their size, shape, morphology and surface. We discuss some general applicable principles in product engineering and give various examples. Strongly related to this approach are methods to characterize and to tailor product and particle properties. For systems which are controlled by the interfaces (e.g. particles in the micron size range and below) we apply a multi-scale approach from the particulate interfaces over particle interactions to the macroscopic properties. Thus, we tailor macroscopic product properties through microscopic control of the interfaces. This approach must be complemented by methods to characteri zeparticle and product properties. It is shown that by careful consideration of the underlying physical processes considerable progress can be achieved.     

Predicting the mode of flow in pneumatic conveying systems-- A review

An initial prediction of the particulate mode of flow in pneumatic conveying systems is beneficial as this knowledge can provide clearer direction to the pneumatic conveying design process. There are three general categories of modes of flow, two dense flows： fluidised dense phase and plug flow, and dilute phase oniy. Detailed in this paper is a review of the commonly used and available techniques for predicting mode of flow. Two types of predictive charts were defined： basic particle parameter based （e.g. particle size and density） and air-particle parameter based （e.g. permeability and de-aeration）. The basic particle techniques were found to have strong and weak areas of predictive ability, on the basis of a comparison with data from materials with known mode of flow capability. It was found that there was only slight improvement in predictive ability when the particle density was replaced by loose-poured bulk density in the basic parameter techniques. The air-particle-parameter-based techniques also showed well-defined regions for mode of flow prediction though the data set used was smaller than that for the basic techniques. Also, it was found to be difficult to utilise de-aeration values from different researchers and subsequently, an air-particle-based technique was developed which does not require any de-aeration parameter in its assessment.     

IDENTIFICATION OF ELASTIC-PLASTIC MECHANICAL PROPERTIES FOR BIMETALLIC SHEETS BY HYBRID-INVERSE APPROACH

Analysis, evaluation and interpretation of measured signals become important components in engineering research and practice, especially for material characteristic parameters which can not be obtained directly by experimental measurements. The present paper proposes a hybrid-inverse analysis method for the identification of the nonlinear material parameters of any individual component from the mechanical responses of a global composite. The method couples experimental approach, numerical simulation with inverse search method. The experimental approach is used to provide basic data. Then parameter identification and numerical simulation are utilized to identify elasto-plastic material properties by the experimental data obtained and inverse searching algorithm. A numerical example of a stainless steel clad copper sheet is consid- ered to verify and show the applicability of the proposed hybrid-inverse method. In this example, a set of material parameters in an elasto-plastic constitutive model have been identified by using the obtained experimental data.     

Scalable gas-phase processes to create nanostructured particles

The properties of nanoparticles are often different from those of larger grains of the same solid material because of their very large specific surface area. This enables many novel applications, but properties such as agglomeration can also hinder their potential use. By creating nanostructured particles one can take optimum benefit from the desired properties while minimizing the adverse effects. We aim at developing high-precision routes for scalable production of nanostructured particles. Two gas-phase synthesis routes are explored. The first one - covering nanoparticles with a continuous layer - is carried out using atomic layer deposition in a fluidized bed. Through fluidization, the full surface area of the nanoparticles becomes available. With this process, particles can be coated with an ultra-thin film of constant and well-tunable thickness. For the second route - attaching nanoparticles to larger particles - a novel approach using electrostatic forces is demonstrated. The micron-sized particles are charged with one polarity using tribocharging. Using electrospraying, a spray of charged nanoparticles with opposite polarity is generated. Their charge prevents agglomeration, while it enhances efficient deposition at the surface of the host particle. While the proposed processes offer good potential for scale-up, further work is needed to realize large-scale processes.     

DROPLETS AND PARTICLES IN SPRAYS： TAILORING PARTICLE PROPERTIES WITHIN SPRAY PROCESSES

Particle generation via atomization and spray processes is a widely applied method for powder production.By means of atomization processes, the relevant particle properties may be tailored to the powder user‘s need in a wide range. Understanding and control of the main subprocesses of atomization is a key feature for choosing a suitable type of spray process and operation conditions. Tailoring particle properties and extending the applications of particle production beyond the current limits is also possible in this way. This contribution highlights some features of spray processes for powder production, namely the gas- and fluid-dynamic processes involved, the materials-related subprocesses, and the formation of the multiphase flow in the spray. As an example, the production of fibre- or sphere-shaped particles from melt atomization is discussed.     

PREDICTION OF THE VISCOELASTIC PROPERTIES OF THE EQUIVALENT PARTICLE FOR THE INTERCALATED MULTI-LAYER STACK OF NANOPLASTICS

The aim of this paper is to apply the asymptotic homogenization method to deter- mining analytically and numerically the transversely isotropic viscoelastic relaxation moduli of the equivalent particle for the intercalated multi-layer stack of intercalated type nanoplastics.A two-phase multilayered material containing n layers is considered.The matrix is assumed to be an isotropic viscoelastic standard linear body and the reinforcement is assumed to be an isotropic elastic body.Final explicit analytical formulae for the effective elastic moduli of the multilay- ered material are derived first;and then the correspondence principle is employed to obtain the homogenized relaxation moduli of the equivalent intercalated particle.A numerical example is given.Final explicit analytical formulae in the time domain derived here make it convenient to estimate the influence of all the particle parameters of micro-structural details on the effective properties of the equivalent intercalated particle.The results of this paper can also be applied to multi-layer composites.     

Product design based on discrete particle modeling of a fluidized bed granulator

Fluidized bed agglomeration is a process commonly used to construct powdered food or pharmaceuti cal products to improve their instant properties. This works analyzes the influence of a wide range of operating parameters （i.e., fluidization air flow rate, temperature, and liquid injection rate） on growth rate, process stability, and product particle structure. Different granulator configurations （i.e., top spray, Wurster coater, spouted bed） are compared using identical process parameters. The impacts of both pro cess variables and granulator geometry on the fluidization regime, the particle and collision dynamics, and the resulting product structure and corresponding properties are studied in detailed simulations using a discrete particle model （DPM） and labscale agglomeration experiments with amorphous dextrose syrup （DE21）. The combination of numerical and experimental results allows to correlate the kinetics of micro scale particle interactions and the final product properties （i.e., agglomerate structure and strength）. In conclusion, detailed DPM simulations are proven as a valuable tool for knowledgebased product design.     

ELECTROSTATICALLY SUPPORTED MIXING OF FINE GRAINED PARTICLES

The processing of fine-grained particles with diameters between 1 and 10 microns is difficult due to strong van-der-Waals attraction forces. In order to improve the handling properties, the fine-grained particles, i.e. host-particles,are coated with various nanoparticles, i.e. guest-particles. The mixing of fine-grained powders is influenced by particle-particle interactions. If these forces are distinctively used, both interactive and ordered mixtu.res can be produced.These particle mixtures consist of composite-particles that have new physical properties. These modified properties depend strongly on the coating process, the diameter- and mass-relationship of the guest- and the host-particles. The properties of the composite-particles can systematically be adjusted to the requirements of industrial applications. For example, a laboratory bubbling fluidized bed can be used to describe the conveying behavior of the functionalized host-particles. Applications for the functionalized particles are in the pharmaceutical and the powder coating industries,e.g. enhanced dry powder inhalers and thin lacquer films. The present research compares three different mixing/coating processes. The composite-particles are characterized by TEM, SEM and with their fluidization characteristics. The coating process itself is monitored by the electrostatic charge of the particles.     

On the energy conservation and critical velocities for the propagation of a ＂steady-shock＂ wave in a bar made of cellular material

The propagation of shock waves in a cellular bar is systematically studied in the framework of continuum solids by adopting two idealized material models, viz. the dynamic rigid, perfectly plastic, locking （D-R-PP-L） model and the dynamic rigid, linear hardening plastic, locking （D-R-LHP-L） model, both considering the effects of strain-rate on the material properties. The shock wave speed relevant to these two models is derived. Consider the case of a bar made of one of such material with initial length L 0 and initial velocity v i impinging onto a rigid target. The variations of the stress, strain, particle velocity, specific internal energy across the shock wave and the cease distance of shock wave are all determined analytically. In particular the ＂energy conservation condition＂ and the ＂kinematic existence condition＂ as proposed by Tan et al. （2005） is re-examined, showing that the ＂energy conservation condition＂ and the consequent ＂critical velocity＂, i.e. the shock can only be generated and sustained in R-PP-L bars when the impact velocity is above this critical velocity, is incorrect. Instead, with elastic deformation, strain-hardening and strain-rate sensitivity of the cellular materials being considered, it is appropriate to redefine a first and a second critical impact velocity for the existence and propagation of shock waves in cellular solids. Starting from the basic relations for shock wave propagating in D-R-LHP-L cellular materials, a new method for inversely determining the dynamic stress-strain curve for cellular materials is proposed. By using e.g. a combination of Taylor bar and Hopkinson pressure bar impact experimental technique, the dynamic stress-strain curve of aluminum foam could bedetermined. Finally, it is demonstrated that this new formulation of shock theory in this one-dimensional stress state can be generalized to shocks in a one-dimensional strain state, i.e. for the case of plate impact on cellular materials, by simply making proper replacements of the elastic and plastic constants.     

MICROMECHANICS OF ROUGH SURFACE ADHESION： A HOMOGENIZED PROJECTION METHOD

A quasistatic homogenized projection is made to characterize the effective cohesive zone behavior for rough-surface adhesion. In the context of the homogenized projection, the traction versus separation relation for the homogenized cohesive zone （HCZ） of a rough interface can be highly oscillatory due to instabilities during microscopic adhesion and decohesion processes. The instabilities are found to occur not only individually but also collectively among the adhesive micro-asperity contacts, leading to extensive energy dissipation. Based on the behaviors of the HCZ relations, a framework for describing instability-induced energy dissipation in rough-surface adhesion is proposed to elucidate the effect of roughness on apparent interface adhesion. Two non- dimensional parameters, α related to roughness morphology and n related to flaw distribution, are identified to be most crucial for controlling the energy dissipation. For an interface with a shallow roughness and a strong intrinsic adhesive strength, the interface adhesion can be stronger if we make it rougher （reducing α） or lower its flaw density （increasing n）. The HCZ projection method can be potentially extended and employed to bridge the apparent adhesion from intrinsic adhesion properties for engineering surfaces with multi-scale shallow roughness.     

PRODUCT ENGINEERING OF PARTICULATE SOLIDS

An important development in Particle Technology is directed towards tailored product properties, i.e. product engineering. Product properties are strongly related to the disperse properties of the particles, i.e. their size, shape, morphology and surface. We discuss some general applicable principles in product engineering and give various examples. Strongly related to this approach are methods to characterize and to tailor product and particle properties. For systems which are controlled by the interfaces (e.g. particles in the micron size range and below) we apply a multi-scale approach from the particulate interfaces over particle interactions to the macroscopic properties. Thus, we tailor macroscopic product properties through microscopic control of the interfaces. This approach must be complemented by methods to characterize particle and product properties. It is shown that by careful consideration of the underlying physical processes considerable progress can be achieved.     

Cotransport of Graphene Oxide Nanoparticles and Kaolinite Colloids in Porous Media

Optimising production from heterogeneous and anisotropic reservoirs challenges the modern hydrocarbon industry because such reservoirs exhibit extreme inter-well variability making them very hard to model. Reasonable reservoir models can be obtained using modern geostatistical techniques, but all of them rely on significant variability in the reservoir only occurring at a scale at or larger than the inter-well spacing. In this paper we take a different, generic approach. We have developed a method for constructing realistic synthetic heterogeneous and anisotropic reservoirs which can be made to represent the reservoir under test. The main physical properties of these synthetic reservoirs are distributed fractally. The models are fully controlled and reproducible and can be extended to model multiple facies reservoir types. This paper shows how the models can be constructed and how they have been tested. Reservoir simulation results of a number of generated 3-D heterogeneous and anisotropic models show that heterogeneity, in terms of only the geometric distribution of reservoir properties, has a little effect on oil production from high and moderate quality reservoirs. However, if the effect of heterogeneity on capillary pressure is taken into account, the effect becomes striking, where varying the heterogeneity of reservoirs properties can lead to a 70 % change in the predicted oil production rate and a significant early shift of water breakthrough time. Hence, it is the heterogeneity consequences that are really substantial if not taken into account. These are very significant uncertainties for a hydrocarbon company if the heterogeneity of their reservoir is not well defined.     

爆炸与冲击动力学若干问题研究进展

介绍了爆炸与冲击动力学数值模拟领域近几年的研究重点及主要进展.包括材料本构关系、损伤破坏、冲击相变、射流和微喷等,其中材料本构关系的发展比较系统,有几个典型的模型可以参考,不仅应用广泛,而且有实验数据进行检验和对比.损伤模型只有唯象模型,虽然有不同的物理机制,但缺少直接的实验依据.射流的工程应用比较广泛,理论研究比较缺乏.微喷研究基本停留在定性阶段.随着实验技术及测量手段的发展,相关领域取得了一些令人欣慰的进展.     

Parameters for Modeling Stranded Cables as Structural Beams

This paper presents a method for determining the effective homogenous beam parameters for stranded cables made up of non-homogenous wires, as well as characterization of the attachment method commonly used for cable harnesses on space structures. There is not yet a predictive model for quantifying the structural impact of cable harnesses on space flight structures, and towards this goal, the authors aim to predict cable resonance behavior from basic cable measurements. Cables can be modeled as shear beams, but the shear beam model assumes a homogenous, isotropic material, which a stranded cable is not. Thus, the cable-beam model requires both knowledge of the cable constraints and calculation of effectively homogenous properties, including density, area, bending stiffness, and modulus of rigidity to predict the natural frequencies of the cable. Through a combination of measurement and correction factors, upper and lower bounds for effective cable properties and attachment stiffness are calculated and shown to be effective in a cable-beam model for natural frequency prediction. Although the cables investigated are spaceflight cables, the method can be applied to any stranded cable for which the constituent material properties can be determined.     

Towards Sensitizing the Nonlinear v 2 − f Model to Turbulence Structures

In this paper a one-way coupling between the nonlinear v ² − f model by Pettersson Reif (Flow Turbul Combust 76:241–256, 2006) and an algebraic structure-based model have been investigated. Comparisons with available experimental and numerical data indicate that the compatibility between the two models is good and that their joint performance is satisfactory in the cases considered here. A full coupling between the models seems therefore a potentially viable route towards a significant advancement of engineering turbulence models and their predictive capabilities.     

Aluminum-reinforced epoxy models

This paper discusses test applications, fabrication methods, and stress-analysis techniques which have been developed on aluminum-filled epoxy models. The use of aluminum-reinforced epoxy models as a preliminary design tool has found extensive application in the development and modification of aircraft structures and related components. The range of uses has varied from the effects of adding or removing material in order to optimize a design, to a full experimental stress analysis of a complete part under multiple-loading conditions. This technique when used in conjunction with photoelastic coatings and/or strain gages, provides complete kinematic and design information before production, tooling, manufacturing and engineering expenses are incurred. The paper discusses machined and molded models, material properties including time-modulus criteria and viscoelastic-creep phenomena, model rework, photoelastic-coating reinforcement and strain-gage effects.     

Recent progress on finite element model updating: From linearity to nonlinearity

有限元分析在实际工程中得到了广泛应用.然而有限元模型由于受到网格划分、边界条件和材料物理参数不确定性等的影响,与真实结构有差异. 因此须通过试验数据加以修正,使其尽可能接近实际结构,以保证之后的结构动力模拟分析和监测等具有实际意义. 经过多年发展,有限元模型修正技术已经能够成功应用于一些实际工程,但现代工程技术的进步对有限元模型修正提出了更高要求,修正后的有限元模型不仅要有较高的精确度,还需要为后续应用给出具有指导意义的置信度.而现有的有限元模型修正、确认方法多基于结构线性的假设,而未能考虑实际结构中广泛存在的非线性.因此本文以土木工程结构模型修正的一些研究成果为例,通过对传统有限元模型修正的发展历程进行全面回顾;总结评述传统有限元修正技术的主要方法,以及包括有限元模型确认在内的最新研究进展;重点探讨有限元模型修正技术向非线性发展的技术路线和目前主要研究成果,展望其未来发展方向, 并提出值得研究的问题.     

Equivalent models of corrugated panels

The design of corrugated panels has wide application in engineering. For example corrugated panels are often used in roof structures in civil engineering. More recently corrugated laminates have been suggested as a good solution for morphing aircraft skins due to their extremely anisotropic behaviour. The optimal design of these structures requires simple models of the panels or skins that may be incorporated into multi-disciplinary system models. Thus equivalent material models are required that retain the dependence on the geometric parameters of the corrugated skins or panels. An homogenisation-based analytical model, which could be used for any corrugation shape, is suggested in this paper. This method is based on a simplified geometry for a unit-cell and the stiffness properties of original sheet. This paper outlines such a modelling strategy, gives explicit expressions to calculate the equivalent material properties, and demonstrates the performance of the approach using two popular corrugation shapes.     

有限元模型修正研究进展:从线性到非线性

有限元分析在实际工程中得到了广泛应用.然而有限元模型由于受到网格划分、边界条件和材料物理参数不确定性等的影响,与真实结构有差异. 因此须通过试验数据加以修正,使其尽可能接近实际结构,以保证之后的结构动力模拟分析和监测等具有实际意义. 经过多年发展,有限元模型修正技术已经能够成功应用于一些实际工程,但现代工程技术的进步对有限元模型修正提出了更高要求,修正后的有限元模型不仅要有较高的精确度,还需要为后续应用给出具有指导意义的置信度.而现有的有限元模型修正、确认方法多基于结构线性的假设,而未能考虑实际结构中广泛存在的非线性.因此本文以土木工程结构模型修正的一些研究成果为例,通过对传统有限元模型修正的发展历程进行全面回顾;总结评述传统有限元修正技术的主要方法,以及包括有限元模型确认在内的最新研究进展;重点探讨有限元模型修正技术向非线性发展的技术路线和目前主要研究成果,展望其未来发展方向, 并提出值得研究的问题.      

Microstructure constitutive equation for discotic nematic liquid crystalline materials –

The rheological material functions predicted by a previously selected constitutive equation (CE) for discotic mesophases are presented. The predicted relations among rheological properties, shear-induced microstructure, processing conditions and material parameters of discotic mesophases are characterized and discussed. The first and second normal stress differences corresponding to planar (i.e., 2-D orientation) microstructure mode of discotic nematics are found to be qualitatively similar to those for rod-like nematics despite the existing differences in flow-orientation characteristics. The first (second) normal stress difference for discotic mesophases corresponding to non-planar (i.e., 3-D orientation) microstructure mode is always positive (positive or negative depending on viscous effects) and is found to be due to flow-induced biaxiality. The effect of change in nematic potential (or temperature) on rheological properties of discotic mesophases is also presented. The apparent shear viscosities for various microstructure modes and material properties are also presented and shown to agree qualitatively with the available experimental data. Though only restricted validation of the predicted results with the actual experimental data of discotics is possible, the present study provides essential theoretical feedback to the on-going experimental work being pursued in understanding the processing behavior of mesophase pitches. Received: 24 February 1998 Accepted: 15 May 1998