A mechanical model for dimensional instability in moisture-sensitive fiber networks

A nonlinear finite element model is developed to simulate the mechanical behavior of fiber networks exposed to moisture. The full-scale three-dimensional Reissner beam model is geometrically nonlinear and handle large deformations and rotations and can be applied to simulate any moisture-sensitive fiber-based network material. Moisture in the surrounding air is transported into the fibers, which leads to chiral curl of individual fibers, which in turn introduce stresses in the network since the fibers are connected to other fibers in a complex manner. Deformations of networks subjected to various degrees of moisture are analyzed. The effects of fiber orientation and network geometry are examined. Numerical results obtained with the model show qualitative agreement to experimental results reported in literature on cellulose materials.