Sequentially-Coupled Finite Element Transient Analysis with Hygroscopic Swelling

The characterization of the hygroscopic property for the packaging materials presents unique challenges, which are not adequately addressed in current methods. One of those challenges is the impact of non-uniform moisture distribution across the specimen. Our recent studies have shown that the current averaged approach might overestimate the coefficient of hygroscopic swelling as much as 250%. In our previous analysis, however, the hygroscopic stress induced deformation has not been taken into consideration. As a matter of fact, due to non-uniform moisture distribution during the test, the total measured deformation includes the hygroscopic swelling itself, and the hygroscopic stress induced deformation. In this paper, a comprehensive study is performed on the impacts of non-uniform moisture distribution and the effect of hygroscopic stress by using sequentially coupled moisture diffusion and hygroscopic stress modeling approach. The results show that the hygroscopic stress induced displacement is relatively small, although the elastic strain caused by the hygroscopic stress accounts for about one third of the total strain. The results in our previous study are proved to be acceptably accurate, even through the hygroscopic stress induced elastic deformation has been neglected