Diffusion with micro-sorption in bentonite: evaluation by molecular dynamics and homogenization analysis

We here give a numerical analysis method of a diffusion problem including sorption chemistry for bentonite clay. Bentonite predominantly consists of the microscopic smectitic clay minerals (mainly montmorillonite and beidellite). Physico-chemical properties of smectite clays such as diffusivity of chemical species and adsorptivity on surface of clay mineral are characterized by crystalline structure of hydrated smectite minerals. To obtain the microscopic properties of the hydrated smectite, the molecular behavior is analyzed by a molecular dynamic (MD) simulation. We understand at least two types of adsorption are formed on the smectite surface; outer sphere complex and inner sphere complex. The inner sphere complex occurs on the edge sites of clay minerals. The amount of mono-layer of cations on the edge surface is considered as the adsorptivity of smectite in the microscopic level. A multiscale homogenization analysis (HA) is applied to extend the microscopic characteristics of the hydrated smectite to the macroscopic behavior. The diffusion and adsorption of a radioactive specie, cesium (Cs), is introduced by this analysis. The calculated results appear to be acceptable.     

An application of a homogenization method to the estimation of effective thermal conductivity of a hydrogen storage alloy bed considering variation of contact conditions between alloy particles

A homogenization method is applied to the estimation of effective thermal conductivity of a hydrogen storage alloy bed. By including the contact conditions between the alloy particles, the effect of contact conditions on the thermal conductivity is investigated.     

印尼某海滨砂钒钛磁铁矿物质组成研究

摘要:印尼某海滨砂钒钛磁铁矿工艺矿物学研究表明,该矿中多数钛磁铁矿是磁铁矿—钛铁晶石—镁铝(铁)尖晶石组成的均一固溶体,钛磁铁矿含TFe≥59%,TiO2 11.5%～12%,Al2O34%,MgO3%,钛磁铁矿单体解离度较高,少部分和脉石形成富连生体。钛铁矿有粒状和片晶状两种,它们都是钛铁矿和赤铁矿的均一固溶体。在矿石性质的基础上,阐明了矿石可选性。随着共伴生高温石英长石的进一步发现,钛磁铁矿和钛铁矿的火山成因得到佐证。      

Upper bound limit analysis model for FRP–reinforced masonry curved structures. Part II: Structural analyses

A homogenized full 3D limit analysis model for the evaluation of collapse loads of FRP–reinforced masonry vaults is presented. Six-noded rigid infinitely resistant wedges are used to model masonry. Three-noded rigid infinitely resistant triangles are used to model FRP strips. Plastic dissipation is allowed only at the interfaces between adjoining elements. Unreinforced masonry homogenized failure surfaces obtained in Part I of the present paper are used to evaluate plastic dissipation at the interfaces between masonry/masonry elements. A possible dissipation at the interfaces between FRP triangles and masonry wedges is also considered in order to take into account, in an approximate but effective way, the possible delamination of the strips from the supports. Italian code CNR DT 200 [CNR-DT 200, 2006. Guide for the design and construction of externally bonded FRP systems for strengthening existing structures. C.N.R., National Research Council, Italy; 2006.] formulas are used to evaluate peak interface tangential strength. While the delamination from the support can be modelled only in an approximate way within limit analysis, the aim of the paper is to accurately reproduce the change in the failure mechanism observed in experimentations due to the introduction of strengthening elements.A 3D approach to model masonry is used in order to take into account the presence of FRP strips either at the extrados or at the intrados of the vaults.Several numerical examples are analyzed, consisting of two different typologies of masonry arches (a parabolic vault and an arch in a so-called “skew” disposition), a ribbed cross vault, a hemispherical dome and a cloister vault. For all the examples presented, both the unreinforced and FRP-reinforced case are discussed. Additional non-linear FE analyses are performed, modeling masonry through an equivalent macroscopic material with orthotropic behavior at failure and possible softening, in order to assess limit analysis results. Comparisons with experimental evidences, where available, are finally reported.Reliable predictions of collapse loads and failure mechanisms are obtained with the model proposed for all the cases analyzed, meaning that the approach proposed may be used by practitioners for a fast and reliable evaluation of the effectiveness of a strengthening intervention.     

Effective conductive properties of open-cell foams

The work is devoted to the problem of simulation of the effective electro and thermoconductive properties of open-cell foam materials with slim highly conductive ligaments. The solution of this problem depends on two small parameters: the ratio of the typical length and the cross-section size of the ligaments, and the ratio of the conductivities of the host medium and the ligaments. The principal terms of the asymptotic solutions (with respect to these parameters) for the fields inside the ligaments are obtained and used in the framework of a finite element method for the numerical simulation of the fields inside the representative volume element (RVE) of the foam material. The Laguerre tessellation procedure is applied for simulation of foam microstructures with various distributions of cell-sizes inside the RVE. Effective conductivity constants of the foams are obtained by averaging the detailed fields over the RVE. The number of cells inside the RVE for reliable calculations of the effective conductivities is indicated. Dependences of the effective conductive properties of the foams on the shapes of the ligaments and the distribution law of the cell-sizes are obtained and analyzed.     

Finite element simulation of deformation behavior of semi-crystalline polymers with multi-spherulitic mesostructure

Elasto-viscoplastic deformation behavior of semi-crystalline polymer with multi-spherulitic mesostructure was investigated using large deformation finite element homogenization method. Multi-spherulitic mesostructure was modeled in representation volume element (RVE) by Voronoi polygons, and the deformation behavior during tension in different directions was numerically investigated. Mesoscopic stress strain relations were almost similar for different mesoscopic structures except for a quarter spherulite mesoscopic models, and its anisotropy decreased with increase in the number of spherulites in RVE. Although anisotropy in mesoscopic stress strain relation disappeared for enough number of spherulites, highly heterogeneous distribution of local strain and stress was observed in each spherulite. Distribution of lamellar orientation in the spherulite caused the heterogeneity and played an important role in the local deformation field.     

基于均匀化理论粘弹性复合材料松弛规律的研究

基于均匀化理论研究了粘弹性复合材料的松驰规律,推导出了均匀化方法计算等效松驰模量的一般形式。在Laplace域中计算等效松弛模量,并用最小二乘法拟合Prony级数表示的松弛函数,然后在时间域中进行数值的Laplace逆转换,得到时间域内等效复合模量。给出了算例来验证这个计算方法的可行性并讨论了松弛模量随夹杂体积分数变化的规律。     

均匀化理论在多孔板结构优化中的应用研究

多尺度均匀化理论自从上世纪 70年代产生以来 ,就被认为是确定复合材料当量性能的一种不可替代的方法。本文将多尺度均匀化方法应用于基于有限元分析的多孔板结构优化设计中 ,简述了求解当量板有效弹性常数的均匀化理论 ,在此基础上 ,建立了基于有限元分析的多孔板结构优化流程 ,编写了FORTRAN程序 ,并将其与AN SYS软件相连接 ,完成了一个多孔板结构的优化设计 ,所得结果表明 ,它能够满足工程应用的需要 ,并为多孔板结构设计提供了一种新思路     

Homogenized properties of elastic–viscoplastic composites with periodic internal structures

A homogenization theory for elastic–viscoplastic composites with periodic internal structures is developed in rate and incremental forms by considering unit cells subjected to macroscopically uniform stress and strain. The theory enables us to incrementally compute the macroscopic as well as the microscopic stress and strain states in nonlinear time-dependent periodic composites. The theory is effective for problems in which the history of either macro-strain or macro-stress, or a combination of them, is prescribed as a function of time. As applications of the theory, transverse and off-axial deformation problems of metal matrix composites reinforced unidirectionally with continuous fibers are analyzed to discuss the effects of fiber arrangement and orientation on the macroscopic deformation behavior.