Large Deformation Nonlinear Response of Soft Composite Structures via Laminate Analogy

The large deformation behavior of fiber preform and angle ply composites with very soft matrix is the subject of this paper. For these materials, large strains and therefore significant changes in the fiber orientations occur due to the application of small traction, thus drastically changing their mechanical properties. The present method uses a laminate analogy model with very low stiffness matrix to compute the finite element properties. The assumptions are that fibers do not elongate, the laminate is made of symmetrically woven fibers and that during a finite element step the properties can be considered constant. Based on these assumptions, a simple way to compute the fiber angle changes is proposed. It is noted that a rectangular box on the soft matrix composite with fibers as its diagonal will deform into a box of different aspect ratio. The large displacement approach is valid since the properties depend on the global Poisson's ratio computation that is proved accurate. A traction test is simulated to demonstrate the method.