Computational Tracking of Composite Manufacturing with Fiber Preforms

The use of braided fiber preforms is a cost-effective process for the manufacturing of composite aircraft structures. For a rational design, it is necessary to predict the fiber orientations in the composite structure after molding. Whenever the manufacturing process requires the manipulation of fiber weaves, large strains and, therefore, significant changes in the fiber orientations occur due to the application of small traction. This drastically changes the mechanical properties of the final structure. To quantify this effect, a new method to simulate the large deformation behavior of fiber preforms has been developed and is presented. The method uses a laminate analogy model with very low stiffness matrix to compute the finite element properties. The assumptions are made that fibers do not elongate, the laminate is made of symmetrically woven fibers, and that, during a finite element step, the properties can be assumed constant. Based on these assumptions, a simple way to compute the fiber changes is proposed, as it is remarked that a box 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 ratio computation that is proved accurate. The method is then demonstrated by an example, where a fiber weave preform is shaped over a mold. The resulting fiber orientations are analyzed to evaluate the effect of the manufacturing process on structure properties and durability. The advantage of the present method is further demonstrated by evaluating the damage tolerance of the composite structure via progressive fracture.