Comparison of continuous fiber and Stretch Broken Carbon Fiber (SBCF) materials in forming processes

Newly developed Stretch Broken Carbon Fiber (SBCF) materials offer the potential to expand the range of feasible part shapes in automated diaphragm forming. Extensibility along the axis of reinforcement may decrease the levels of inter-ply and intra-ply shears required to allow thermoset prepreg systems to conform to complex shapes. In order to assess the formability of woven and unidirectional prepreg systems based on SBCF materials, a series of forming trials was conducted at Rensselaer Polytechnic Institute using a reconfigurable tool comprised of an array of independently controllable pins. A range of part shapes, including, boxes, L - Stiffeners, ellipsoids, C- channels and V-channels, was formed from both SBCF prepregs and equivalent continuous fiber materials. Preprinted orthogonal grid patterns were used to capture surface shear patterns, and these provided the principal bases for comparison of the respective deformation modes. Results consistently showed that lower levels of shear were required in the SBCF materials, though post-forming shape fidelity was superior. This suggests that, while dramatic differences in part quality were not noted, the SBCF materials provided a deformation mode that reduced the level of shear required. It is proposed that this deformation mode is stretching along the fiber axis.