THE FUTURE OF ADDITIVE TECHNOLOGIES
IS IN ANISOPRINTED COMPOSITES
Composite materials have a heterogeneous internal structure, as a result, they are extensively used in the aerospace, automotive and civil engineering sectors. The main characteristic of such materials is the presence of two different phases: matrix, or binder, and reinforcement. The reinforcement resists the main loads, while the matrix makes the individual reinforcement elements work together. In structural composites, high-strength fibers such as carbon, glass or organic are used as the reinforcement element, providing significantly higher specific strength and stiffness compared with any metal.
Matrices are predominantly polymers, although composites based on metallic, ceramic and other types of binders are widely known. The main feature of such fibrous composites is their anisotropic properties. That is, the material response to external loads depends significantly on the direction of these loads. For example, the cCFRP ((continuous) carbon fiber reinforced polymer) strength differs by two orders of magnitude depending on whether the load is applied along the direction of the fibers, or transversely. Traditionally, this feature of composite materials is considered to be one of their main disadvantages, limiting their mass use in most industries. The anisotropy is hardly repulsed, mainly by making so-called quasi-isotropic laminates – or sheet materials – in which the layers of a unidirectional composite are stacked at different angles. This results in material behaviour comparable with metal sheet in a plane stress state. Furthermore, with the exception of the moulding step, they are often used in exactly the same way: cut, drilled, connected with rivets and bolts, which destroys the integrity of the reinforcing fibers, which in turn leads to additional stress concentrations due to the free edge effect and other features inherent in composite materials that reduce the overall strength of the structure.