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Our investigations of the cation exchange resins based on styrene-divinylbenzene (DVB) have shown that because of its unfavorable reactivity towards styrene, the DVB causes great inhomogeneities in the copolymers formed with styrene. This affects, in a negative way, the mechanical stability of the strongly acid cation exchange resin produced. On the other hand, strongly acid cation exchange resins based on polystyrene may be produced by reacting polystyrene in two steps with chlorosulfonic acid in the presence of formaldehyde. Furthermore, it has been successfully tied to chloromethylate polystyrene in the presence of paraformaldehyde or methylal so that a cross-linked chloromethylated product was formed. It has been the aim of our investigations to make sure if, on the one hand, on the basis of polystyrene, it was possible by chloromethylation to get a cross-linked product that could be subsequently worked into a strongly acid cation exchange resin or, on the other hand, to verify if one could, based on polystyrene in the presence of a formaldehyde-releasing substance, sulfonate in one step so that the product is cross-linked at the same time. The quality criterion of all experiments is to guarantee that the characteristics of the final product, i.e., a strongly acid cation exchange resin, are comparable to those of the well-known resin types based on styrene-DVB.

In the present contribution we extend a previously proposed so-called solid–shell concept which incorporates only displacement degrees of freedom to the simulation of large elastic and large elastoplastic deformations of shells. Therefore, the modi cations necessary for hyper-elastic or elastoplastic material laws are discussed. These modi cations concern the right Cauchy–Green tensor for large elastic deformations, respectively, the deformation gradient for elastoplasticity which then are consistent to the modi ed Green–Lagrange strains that are necessary for transverse shear and membrane locking free solid–shell element formulations. However, in addition to the locking mentioned above especially in the range of plasticity incompressibility locking becomes important. Thus, the second major aspect of this contribution is the discussion of several ways to avoid incompressibility locking also including the investigation of eigenmodes. Finally, a selective reduced integration scheme with reduced integration for the volumetric term is employed and described in detail, although it is limited to material laws which allow the decomposition into a volumetric and a deviatoric part. Some numerical examples show the range of application for the proposed elements. Copyright ? 2000 John Wiley & Sons, Ltd.

In the present contribution we propose a so-called solid-shell concept which incorporates only displacement degrees of freedom. Thus, some major disadvantages of the usually used degenerated shell concept are overcome. These disadvantages are related to boundary conditions—the handling of soft and hard support, the need for special co-ordinate systems at boundaries, the connection with continuum elements—and, in geometrically non-linear analyses, to a complicated update of the rotation vector. First, the kinematics of the so-called solid-shell concept in analogy to the degenerated shell concept are introduced. Then several modifications of the solid-shell concept are proposed to obtain locking-free solid-shell elements, leading also to formulations which allow the use of general three-dimensional material laws and which are also able to represent the normal stresses and strains in thickness direction. Numerical analyses of geometrically linear and non-linear problems are finally performed using solely assumed natural shear strain elements with a linear approximation in in-plane direction. Although some considerations are needed to get comparable boundary conditions in the examples analysed, the solid-shell elements prove to work as good as the degenerated shell elements. The numerical examples show that neither thickness nor shear locking are present even for distorted element shapes. © 1998 John Wiley & Sons, Ltd.

Vielen effizienten Schalenelementen fur FE-Anwendungen liegt das Degenerationskonzept zugrunde, dessen wesentliche Merkmale eine Kinematik mit Rotationsfreiheitsgraden und die Beschrankung auf einen ebenen Spannungszustand sind. Somit erfordern bereits geometrisch nichtlineare Berechnungen aufgrund der Verdrehungsfreiheitsgrade relativ aufwendige Formulierungen, die bei materiell nichtlinearen Berechnungen durch die Forderung nach einem ebenen Spannungszustand wesentlich komplexer werden. Ziel der Studie ist, eine Schalenformulierung vorzustellen, die diese nicht Nachteile aufweist.

The following possible techniques of nitrate removal from drinking water are compared with respect to their efficiency: reserved osmosis, electrodialysis and ion exchange. It can be shown by test products that it is possible, in principle, to synthesize nitrate-selective anion exchange resins. Today it is assumed that from this a preferential position of the technology of ion exchange can be expected for the elimination of nitrate from drinking water.