Date of Award


Document Type


Degree Name

Master of Science (MS)


Mechanical Engineering

Committee Chair/Advisor

Dr. Zhaoxu Meng

Committee Member

Dr. Zhen Li

Committee Member

Dr. Xin Zhao


Natural protective materials offer unparalleled solutions for impact-resistant material designs that are simultaneously lightweight, strong, and tough. Particularly, the dactyl club of mantis shrimp features chitin nanofibrils organized in a Bouligand structure, which has been shown to effectively dissipate high-impact energy during powerful strikes. The mollusk shells also achieve excellent mechanical strength, toughness, and impact resistance with a staggered, layer-by-layer structure. Previous studies have shown that hybrid designs, by combining different bioinspired microstructures, can lead to enhanced mechanical strength and energy dissipation capabilities. Nevertheless, it remains unknown whether combining Bouligand and staggered structures in nanofibrillar cellulose (NFC) films, forming a discontinuous fibrous Bouligand (DFB) architecture, can achieve enhanced impact resistance under localized ballistic impact. Additionally, the failure mechanisms under such dynamic loading conditions have been minimally understood. In this thesis, I present a comprehensive study to investigate the dynamic failure mechanisms and quantify the impact resistance of NFC thin films with DFB architecture by leveraging previously developed coarse-grained models and explicit projectile impact molecular dynamics simulations. The results show that when nanofibrils achieve a critical length with the DFB architecture, the impact resistance of NFC films outperforms the counterpart films with continuous fibrils by comparing their specific ballistic limit velocities and penetration energies. I also look into the underlying mechanisms contributing to this improvement in impact resistance, which include iii enhanced fibril sliding initiated at the discontinuous sites, intralayer and interlayer crack bridging, and crack twisting mechanism in the thickness direction enabled by the DFB architecture. Overall, the results in this thesis show that by combining Bouligand and staggered structures in NFC films, their potential for protective applications can be further improved. The findings presented in this thesis can provide practical guidelines for the design of protective films made of nanofibrils.



To view the content in your browser, please download Adobe Reader or, alternately,
you may Download the file to your hard drive.

NOTE: The latest versions of Adobe Reader do not support viewing PDF files within Firefox on Mac OS and if you are using a modern (Intel) Mac, there is no official plugin for viewing PDF files within the browser window.