聚烯烃粒料重力掺混系统均化原理、掺混试验与工业设计

重力掺混均化技术是在理论指导下,基于实验及试验的工业技术。其原理是：通过控制料仓内各掺混管的工作状态,实现自动均匀取料并相互掺混,达到出料组分均化的目的。解释了聚烯烃装置重力掺混系统常用的两种设计思路的异同,提出了系统设计的原则。     

Variability response functions for apparent material properties

The computation of apparent material properties for a random heterogeneous material requires the assumption of a solution field on a finite domain over which the apparent properties are to be computed. In this paper the assumed solution field is taken to be that defined by the shape functions that underpin the finite element method and it is shown that the variance of the apparent properties calculated using the shape functions to define the solution field can be expressed in terms of a variability response function (VRF) that is independent of the marginal distribution and spectral density function of the underlying random heterogeneous material property field. The variance of apparent material properties can be an important consideration in problems where the domain over which the apparent properties are computed is smaller than the representative volume element and the approach introduced here provides an efficient means of calculating that variance and performing sensitivity studies with respect to the characteristics of the material property field. The approach is illustrated using examples involving heat transfer problems and finite elements with linear and nonlinear shape functions and in one and two dimensions. Features of the VRF are described, including dependency on shape and scale of the finite element and the order of the shape functions.     

Numerical homogenization of hardened cement paste

Based upon a three-dimensional computer-tomography of hardened cement paste, a finite-element mesh at micrometer length scale is introduced. Effective material properties are obtained through numerical homogenization techniques using representative volume elements. Statistical tests, two- and three-dimensional computations and a comparison with experimental data are shown. For the hydration products of hardened cement paste a visco-plastic constitutive equation of Perzyna type including isotropic damage is introduced. The inelastic material parameters are identified solving an optimization problem through a combination of a stochastic genetic algorithm and the deterministic Levenberg-Marquardt method. The time-consuming evaluations of the corresponding objective function are distributed within a network environment automatically.     

Thermally induced structural and mechanical variations in ternary Al–Si based alloys

The effect of heat treatment on the variations in the structural and mechanical characteristics of Al–Si based ternary alloys was studied for samples prepared from elements of purity 99.99% and aged at 673 K for 2 h through tensile tests in the temperature range (413–493 K). Softening behaviour was observed with increasing the working temperature. The mechanical results were discussed in relation to the structure analysis of TEM micrographs obtained at room temperature for samples aged at 673 K. Sn addition improved the mechanical properties of the samples but this was not achieved with Ag addition which improved softening and ductility under the same testing conditions.     

Effective behaviour of elastic heterogeneous thin structures at finite deformations

In this contribution the effective material behaviour of thin structures like membranes and plates consisting of heterogeneities is investigated. The diameter of typical inclusions can be in the order of magnitude of the thickness of the membrane or plate. Thus, the prerequisite for a standard homogenization procedure using representative volume elements is not fulfilled anymore, since the required size of an RVE would be larger than the thickness of the structure itself. Additionally the assumption of uniformity of the boundary conditions on the RVE would be violated especially for plates since in general the predominant deformation of such structures is bending. However, it can be shown that the effective behaviour of such heterogeneous thin structures subjected to finite deformations is still in good agreement to the results obtained for homogenized materials.     

Continuous preparation of O/W nano-emulsion by the treatment of a coarse emulsion under subcritical water conditions

A coarse oil-in-water (O/W) emulsion, the oil phase of which was octanoic acid, was prepared at a very low surfactant concentration using a rotor/stator homogenizer. The emulsion was passed in a stainless steel tube immersed in an oil bath at 220 °C at a residence time of 60 s, and then mixed with the surfactant solution to produce a finely dispersed emulsion. The diameter of oil droplets in the fine emulsion was ca. 40 nm at the weight ratio of surfactant to oil of ca. 0.35 or higher.     

Influence of Flow Conditions in High‐Pressure Orifices on Droplet Disruption of Oil‐in‐Water Emulsions

Flow conditions in and behind high‐pressure orifices are described by a characteristic correlation between discharge coefficient and Reynolds number. The use of a pressure vessel and variations in viscosity allowed for non‐pulsating flow conditions from laminar to turbulent flow. Emulsions were homogenized under each condition. A considerable difference was observed in the final droplet size distribution depending on laminar, transitional, and turbulent flow. When the flow was pulsating as found when applying a plungers pump, transition of the flow from laminar to turbulence was more difficult to detect. Emulsions homogenized under these conditions indicated broader droplet size distributions. The Sauter mean diameter, however, was not affected by the pulsating flow.     

Analysis of the effects of rough surfaces in compressible thin film flow by homogenization

A classical problem in lubrication theory is to predict the pressure distribution in a thin fluid film between two surfaces which are in relative motion. If one of the surfaces is rough, then the distance between the surfaces is rapidly oscillating. This leads to that the governing Reynolds partial differential equation involves rapidly oscillating coefficients. The branch in mathematics which considers such types of equations is known as homogenization. In this paper we study the effects of surface roughness for a special type of compressible fluid. In particular, we derive homogenization results connected to the friction force and the load carrying capacity.     

Methodology for nanoindentation-assisted prediction of macroscale elastic properties of high performance cementitious composites

This paper describes a methodology applied for determination of macroscale elastic properties of high performance cementitious composites (HPCC) based on nanoindentation measurements. For that, the elastic properties of HPCC mixtures with quartz filler and fly ash were evaluated at different length scales by nanoindentation (microscale) and the static and dynamic elastic moduli and compressive strength tests (macroscale). The nanoindentation results, obtained from a representative microlevel area by grid indentation with subsequent phase deconvolution, were complemented by an independent porosimetry test and inserted into a two-step analytical homogenization scheme to predict the overall macroscale properties. The final results indicate that the presented methodology allows a reliable advanced prediction of HPCC elastic properties, which is promising for the concrete industry since it would allow for reducing the number of large scale experiments and producing of a more predictable composite in an easier and experimentally less expensive way.