Effects of tablet waviness on the mechanical response of architected multilayered materials: Modeling and experiment

The excellent mechanical properties that biological materials possess are greatly influenced by the geometrical properties of their small scale constituents. Nacre, also known as Mother of Pearl, is an organic-inorganic composite material that makes up the inner layer of seashells. Nacre is observed for its impressive combination of stiffness, strength, and toughness which can be attributed to its waviness and the layering pattern of the brick and mortar structure of ceramic and protein that allows nacre to exhibit great mechanical energy and dissipate it over a large volume. In this study, the effect of this waviness on a model architected multilayered material system is analyzed numerically and experimentally in order to understand its effects on the stiffness, strength, and toughness of nacre. 3-D printed composites with auxetic and nacreous structure were created and tested in tensile boundary conditions. Finite element analysis was used to study the stress distribution and mechanical response of these composites. Results from the finite element models and the mechanical tests results show that increasing the tablet's waviness increases the stiffness, however, there is an optimum value of tablet waviness for the highest strength and tensile toughness. Increasing waviness level can improve the elastic modulus by about 23%, strength by about 65% and toughness by about 42%. Using the proposed modeling approach, more detailed studies can be done on the toughening mechanisms of composite multilayered materials. These results can be used as a guide to design super-tough composites with multilayered structures.