The attempt to replace chlorine in polyphosphonitrilic chloride with alkoxyl groups is successful except that oxygen rather than alkoxyl substitution occurs to some extent. The amount of oxygen substitution and the extent of degradation are minimized if the polyphosphonitrilic chloride is swollen prior to alcoholysis. The substituted product is insoluble until treated with boiling tetrachloroethane. The final products, the esters, are very tacky when pure but can be incorporated with other polymers to give desirable products.
Although bonding has been known for a long time, the mechanical behavior of adhesive bonded joints comes more and more into the focus of scientific attention. During usage, adhesives are exposed to environmental influences like temperature, moisture and radiation. Due to the fact that adhesives usually consist of polymers, these influences change their mechanical behavior. In the presented work, a viscoelastic cross-linked polyurethane that behaves incompressible is investigated. A three-dimensional mechanical model is presented, which takes into consideration influences of changes in temperature as well as in the moisture concentration inside the adhesive layer and its thickness on the mechanical behavior.
ModelingIt is assumed that the adhesive behaves in a viscoelastic manner close to the glass transition temperature. For a description of this behavior, an approach of the Neo-Hooke type [9] is chosen for both the equilibrium as well as for the non-equilibrium parts:In this context, T is the cauchy stress tensor, B the left cauchy green deformation tensor, B j e the elastic left cauchy green deformation tensor of the j th Maxwell element and I the identity of second rank. The Lagrange parameter p assures the incompressibility of the material. The material parameters µ(Θ, χ, d) respectively µ j e (Θ, χ, d) of the equilibrium and the non-equilibrium stiffnesses (see Fig. 1) are formulated as functions depending on the temperature Θ, the moisture χ, and the thickness of the adhesive layer d. For all further considerations, the assumption is made that all influencing properties are constant during the testing of the specimen. Furthermore, because of the heigh value of the heat conductivity of the bonded metal sheets, a temperature gradient inside the specimen can be neglected. Because of the very slow diffusion process of water in the polymer, the moisture distribution can be inhomogeneous. As a result, the distribution of every material parameter can be inhomogeneous as well (see Fig. 2). To investigate this effect, the diffusion behavior has to be determined first.
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