Polymer-Ceramic Composites
It can be learned from nature that the best material properties in terms of strength and resistance to fracture are achieved when very hard (but possibly brittle) materials are joined by very thin layers of a soft but tough material. For example, in the case of tooth enamel and nacre, this is achieved by ceramic materials (hard and brittle) containing 90% or more combined by organic materials in the nanometer range.
Such materials can be artificially reproduced by ceramic-polymer compounds, either by fibrous or spherical ceramic particles.
Spherical particles can be packed very tightly in an orderly fashion (like in an orange box). If one imagines the interior of the orange as a ceramic and the orange peel as a soft organic material (polymer), one can use heat treatment and/or pressure to cause the peels to bond and become a tough yet strong composite material.
Using the finite element method, one can map the geometry and properties of the microstructure and directly simulate both the strength and propagation of cracks by modeling. By varying, for example, the size of the ceramic particles or the polymer layer thickness, it is possible to optimize material properties and provide guidance on how to manufacture specific components. Since the properties of the polymer material in particular can change through the manufacturing process, constant collaboration with experimental characterization and/or atomic scale simulation techniques is essential.
As a current example for the microstructure simulation of composites we are investigating particle-based high-performance composites with a very high volume fraction of the particles. This high particle content is achieved by self-assembly of the particles into a supercrystalline microstructure. Magnetite particles with a diameter of less than 20 nm, surface-coated with oleic acid molecules, are joined to superalloys [Dreyer et al, 2015]. Subsequently, this composite obtains an extraordinary rigidity by heat treatment and associated crosslinking of the organic molecules. The numerical simulation of such a microstructure by unit cell modeling provides the mesoscopic response of the composite material, for which a material model at the next higher hierarchical level is then designed to predict the material response in experiments such as e.g. nanoindentation [Ma et al. 2019, Li et al. 2020].
