Diaphragm forming of carbon fiber reinforced thermoplastic composite materials

The objective of this work was to develop a science based understanding of the diaphragm forming of carbon fiber reinforced thermoplastic laminates. This was achieved through the use of experimental and analytic research techniques.;The experimental work consisted of fabricating composite components and identifying the effects of the forming parameters on the resulting thickness profiles and fiber orientation. The transverse fiber flow produced thickness variations and fiber orientation fields peculiar to the tool surface geometry, diaphragm deformation behavior, and laminate configuration. The transverse flow in the surface ply layers was dominated by the stretching diaphragms. In the interior ply layers the flow appeared to be driven by the pressure gradients produced at the contact points. This created varying reinforcement geometry through the thickness of the formed component.;The analytical work consisted of the development of a diaphragm forming process model which employed engineering mechanics and fiber kinematics to predict post-formed thickness variations and fiber orientation fields of axisymmetric composite components. The computation procedure was broken into three steps that were performed in a quasisteady-state manner. A diaphragm deformation analysis was utilized to determine the pressure boundary condition for the flow analysis. The flow analysis determined the thickness variation and flow velocities in the transverse fiber direction. The flow velocities were employed to determine the relative fiber realignment. The realignment of the fibers was then utilized in a geometric mapping procedure to determine the fiber orientation field.;The thickness profile predictions appeared to capture the geometric effects and the basic trends in the experimentally observed thickness profiles. The maximum thickness values, however, were underpredicted due to the types of boundary conditions employed. The fiber orientation predictions captured the basic realignment behavior of the fibers, but had difficulty mapping fibers onto surfaces when large degrees of fiber movement occurred. Overall, the predictions on interior ply and surface ply layer orientations matched reasonably well with the experimental observations.