Microstructure characterization in direct sheet molding compound

The microstructure of fiber glass bundles used in the direct sheet molding compound (D‐SMC) was investigated in a flat plaque mold. Analyses of the bundle deformation, including bending and deformation of the tow shape, were done for the charge and specific sites within a square plaque part for 30% and 62% of initial charge mold area coverages. Microscopy and micro‐computed tomography (micro‐CT) of the samples clarify the microstructure of the bundles after flow. Samples were taken at different flow locations within the plaque corresponding to increasing flow length from the center. The bundles at the part edge and corner deform more than the bundles close to center of the mold in both initial charge cases. The bundles flattened at all positions and bundle bending was mainly observed at the corner. The tow width changes and tow deflections were higher in the samples of 30% mold area coverage. The micro‐CT images showed that the bundles keep their cohesion and stay straight within the middle of the flow path position, but bend at the edge of the mold. Mold filling simulation using Moldflow™ (Autodesk) predicted fiber tow orientation through the thickness using the reduced‐strain closure (RSC) models for fiber distribution for 30% and 62% initial mold area coverage. The measured value of orientation from micro‐CT images confirms the random orientation through the thickness, consistent with the RSC model. POLYM. COMPOS., 40:E69–E77, 2019. © 2017 Society of Plastics Engineers