Full-field effect of flow-induced fiber orientation during compression molding of carbon fiber sheet molding compounds

An image-based fiber orientation analysis technique has been employed to study the effect of initial charge coverage and preferential fiber alignment on the flow-induced fiber orientations in carbon fiber sheet molding compounds (SMCs). The initial charge coverage area exhibited minimal fiber reorientation while significant fiber alignment in the flow direction was observed in the regions of greatest flow. Novel subsurface analysis using the same full-field orientation analysis technique also showed the presence of a skin-core structure with greater flow-induced fiber alignment at the mold surfaces, while the core retained more of the initial fiber orientation distribution. Edge effects were also revealed by this analysis at the mold walls. Tensile testing from two orthogonal directions showed that panels molded from lower charge coverage resulted in better mechanical performance and lower anisotropy. Moreover, by encouraging charge flow in the preform's preferential alignment direction, high tensile stiffness and strength in the preferred direction were achieved (56.7 GPa and 238.9 MPa, respectively) at 30% fiber volume fraction. This provides a practical demonstration of the value in controlling fiber orientation, with respect to charge positioning and mold flow, to maximize and tailor the composite performance of SMCs typically used for automotive applications. Highlights: Low-cost scanning technique is extended to assess internal fiber orientations Full-field orientations are measured before and after molding Investigation of how charge size and shape can affect orientations Combining effects of flow and initial orientation to tailor SMC performance Circular statistics provides a thorough analysis of orientation distributions.