page_title: CFSMC
section_title: Material Properties
hierarchical_section_title: CFSMC / Material Properties
caption_attribution_description: English: Laminate made of UD plies compared to CF SMC
context_page_description: CFSMC, or Carbon Fiber Sheet Molding Compound, is a ready to mold carbon fiber reinforced polymer composite material used in compression molding. While traditional SMC utilizes chopped glass fibers in a polymer resin, CFSMC utilizes chopped carbon fibers. The length and distribution of the carbon fibers is more regular, homogeneous, and constant than the standard glass SMC. CFSMC offers much higher stiffness and usually higher strength than standard SMC, but at a higher cost.
context_section_description: Due to their heterogeneous and anisotropic microstructure, mechanical properties of CF-SMC can vary significantly within broad ranges. Parameters having profound impact on these materials performances are mainly related to the fibres and matrix neat mechanical and geometrical properties (especially those of the fibres) and the orientation and content of the reinforcement. Modulus can vary from less than 20 GPa to 60 GPa, while strength values are within 60-500 MPa.
  CF-SMC can also be engineered, to some extent, to have better performances in a specific direction, in a similar fashion as continuous fibres composites. This can be achieved by carefully controlling the compression moulding stage to influence fibre orientation. When the fibres are mainly aligned with the loading direction, the material behaviour is mainly dominated by that of the fibres, thus resulting in stronger and stiffer, but also more brittle response. In the opposite case, if fibres tend to dispose perpendicular to the loading direction, the resin contributes more to the load bearing, and the overall composite will be less stiff, less strong and more ductile. Being based on hydrodynamic transport phenomena, however, the control over fibre orientation in CF-SMC is much more limited than in the continuous composites case, where orientation is often directly determined accurately by the manufacturer. In addition, while continuous fibres composites have a specific orientation, short fibre reinforced plastics can have a preferential orientation, meaning that, considering a generic system of axis, the majority of fibres can have a higher component along a direction and a lower component along the other two axis.
  The discontinuous tow-based microstructure of these materials makes is even more heterogeneous than standard composites: fibre ends themselves acts as stress concentration areas for both the resin and the neighbouring tows; moreover, especially for complex shaped parts, it is impossible to prevent some local spots with badly aligned tows (e.g. perpendicular to the direction of axial stress) or with low fibre volume content, like resin pockets. Although making the material weaker and the structural design more complex, this feature makes these materials quite notch-insensitive.
  When moulded, CFSMC has a very different appearance than traditional carbon fibre fabric composites, which traditionally appear with a woven checkerboard pattern. CFSMC has the appearance of black and grey marble or burl.
caption: Comparison of the accurate fibre orientation in a laminate of UD plies (a) and the preferential orientation achievable with CF-SMC (b).
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