Simulation of the Manufacture of Closed Shape Composite Structures

A process model was developed for the fabrication of closed shape composite structures such as thick-wall cylinders, with the emphasis on fiber bundle deformation and its effect on the process physics. A continuum mechanics model for fiber bundle deformation in the composite manufacturing processes was proposed. Based on this model, the winding and consolidation processes for thick wall cylindrical composite structure were analyzed, and a process model was developed. Fiber bundle deformation was considered as the combination of elastic and viscous responses. In some of the manufacturing processes, such as winding, pultrusion, and molding, the elastic response can be dominant. A compliance matrix for the fiber bundle was proposed and three independent compliance terms were evaluated quantitatively by assuming a statistical distribution of imperfect conditions in the fiber bundle. These included small waviness, misalignment, and fiber crossover. These compliance terms were found to be functions of the fiber deformation state, which can be expressed by using the fiber volume fraction. This relationship was then used in the analysis of the winding and consolidation processes. It was found that two constants determined whether the process was an elastic dominated or a fiber deformation/resin flow process. If the winding time was much shorter than the flow time constant, the winding process can be thought as elastic dominant. On the other hand if the flow time constant was much less than the winding time, flow was substantial in the winding. When winding operation was finished, the consolidation of composite layers was also completed. Nonlinear analysis on fiber deformation can be applied in this case. Under general conditions, the process consisted of material deformation coupled with the mass flow. A series of experiments on fiber deformation compliance, fiber motion and distribution in molding, winding and consolidation process time evaluation, and simulation of the winding and consolidation were designed and carried out. Experimental results verified the computer simulation model predictions and helped understanding of various process mechanisms. Thesis Committee: Professor Timothy Gutowski (Chairman) Professor Stanley Backer Professor Rohen Abeyaratne