The damping behaviour of engineering materials is an important structural property that affects the in-service performance and the components service life. Engineering materials such as steel and continuous fibre reinforced polymers are stiff but usually lack in vibration damping performance. A figure of merit of damping, also referred to as loss modulus, is typically used to characterise the damping performance of materials. The loss modulus is the product of the material’s storage modulus and the loss factor. The figure of merit allows one to categorise materials according to their stiffness and energy loss behaviour. As opposed to steel and carbon fibre composites, biological composites such as wood, bone and nacre exhibit remarkably high figure of merit. The combination of high stiffness and excellent damping behaviour is attributed to the smart hierarchical structuring of relatively weak building blocks.
This study aims to investigate the design principles underlying the enhanced damping properties of natural materials in order to replicate these principles using engineering materials. Our goal is to combine high stiffness and high vibration damping behaviour simultaneously. To this end, we assemble inorganic particles in a nacre-like brick-and-mortar structure that is representative of biological composites. Alumina (Al2O3) platelets in different volume fractions are introduced into an epoxy matrix, aligned magnetically and eventually consolidated through resin curing. The Al2O3 platelets are aligned in various three-dimensional orientations to generate reinforcing architectures with structural anisotropy. Control over the orientation of the discontinuous reinforcing phase allows us to tune the composite’s stiffness and vibration damping behaviour. Our results show that the in-plane orientation of platelets increases the storage and loss moduli by 4-times simultaneously. This implies that the nacre-like architecture enhances the composite’s energy dissipating capability without compromising the stiffness of the material. To transfer the excellent damping behaviour of the platelet-reinforced matrices into conventional fibre reinforced composites, we infiltrate continuous fibres with the platelet-containing resin using an additive manufacturing method. With the introduction of fibres the stiffness of the composites is further increased to 35 GPa whilst preserving the good vibration damping behaviour.