Computational tracking of composite manufacturing with fiber preforms

The use of braided fiber preforms is a cost-effective process for the manuf acturing of composite aircraft structures. For a rational design, it is nec essary to predict the fiber orientations in the composite structure after m olding. Whenever the manufacturing process requires the manipulation of fiber weave s, large strains and, therefore, significant changes in the fiber orientati ons occur due to the application of small traction. This drastically change s 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 t hat, during a finite element step, the properties can be assumed constant. Based on these assumptions, a simple way to compute the fiber changes is pr oposed, as it is remarked that a box with fibers as its diagonal will defor m into a box of different aspect ratio. The large displacement approach is valid since the properties depend on the global Poisson ratio computation t hat 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 eva luate the effect of the manufacturing process on structure properties and d urability. The advantage of the present method is further demonstrated by e valuating the damage tolerance of the composite structure via progressive f racture.