[SY-J2] Simulation-based Design of Bioinspired Impact-resistant Nanocellulose Films with Bouligand Microstructure
Invited
The Bouligand structure, which features a helicoidal layup of in-plane uniaxial arranged fibers, has been widely observed in biomaterials with superior impact-resistant properties. However, the underlying mechanisms for the damage tolerance remain poorly understood, posing great challenges for the design and development of bio-inspired materials with optimized microstructures. Interestingly, many bio-sourced nanomaterials such as cellulose nanocrystals (CNCs) achieve helicoidal ordering through self-assembly. As a step towards mimicking impact tolerant biomaterials, here we present systematically coarse-grained molecular dynamics simulations of nanoscale projectiles impacting CNC films with Bouligand structure as a model system. We report the specific ballistic limit velocity and energy absorption as metrics to quantify impact performance of CNC films. We discover that Bouligand structures with low pitch angles (10-30 degrees) show optimal ballistic resistant performance, and significantly outperform quasi-isotropic baseline structures. Intriguingly, decreasing interfacial interactions helps enhance the performance under impact through allowing dissipative inter-fibril and interlayer sliding events to occur more readily without severe fibril fragments. We show that improved interfacial sliding, enhanced wave propagation, larger in-plane crack opening and through-thickness crack twisting contribute to the improved energy dissipation during projectile penetration for CNC Bouligand films with optimal pitch angles. This study reveals structural and chemical factors that govern the optimal design of Bouligand structures made from 1D nanomaterials for protective applications. Concluding remarks will include comparative analyses on other thin film materials, including layered graphitic and metallic nanostructures through scaling and theoretical arguments, as well as potential strategies for mechanical property improvement through better nanocellulose interface design.