Modeling of large deformations in drying viscoelastic materials.

摘要

Adverse influences of changing moisture conditions affect many products, and have significant economic ramifications for industry. For example, variations in humidity lead to the development of residual stresses in composite materials whose constituents have different hygroscopic expansion coefficients. This may cause unwanted effects such as delamination or fracture of fibers, which may render the product unusable instantly, or may significantly shorten the intended life. In particular, this is of concern in the area of electronic devices, which by their very nature are composite. To predict and prevent problems of this kind various quantifying techniques have been developed.This research is dedicated to a group of technologically important problems, involving negative moisture effects on viscoelastic materials, which do not seem to be adequately covered by the available models and techniques. Specifically, large instantaneous elastic deformations, large viscoelastic deformations, large hygroscopic shrinkage, changing material properties and coupling mass transfer with stress analysis characterize these problems. A very important example (because of its scale and cost) of such a problem has to do with drying viscoelastic coatings. There is ample evidence that strains developed in the process of drying can be large and that inelastic deformations are present. Yet, to analyze problems of this sort, very drastic simplifying assumptions of small strain elasticity and elastoplacticity have been used.It is proposed here to formulate and analyze all these effects which have not been considered in the past. Materials used in coatings are typically polymeric they are clearly viscoelastic and they often exhibit large strains. It is expected that the results of the proposed research will complement and aid experimental investigations and will consistute a significant step towards a better understanding and identification of important aspects and parameters of several practical problems.