Mechanical & Materials Engineering, Department of


First Advisor

Florin Bobaru

Date of this Version



A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Mechanical and Materials Engineering, Under the supervision of Professor Florin Bobaru. Lincoln, Nebraska : May 2018.

Copyright (c) 2018 Sneha Akula


Bio-inspired damage resistant models have distinct patterns like brick-mortar, Voronoi, helicoidal etc., which show exceptional damage mitigation against high-velocity impacts. These unique patterns increase damage resistance (in some cases up to 3000 times more than the constituent materials) by effectively dispersing the stress waves produced by the impact. Ability to mimic these structures on a larger scale can be ground-breaking and could be used in numerous applications. Advancements in 3D printing have now made possible fabrication of these patterns with ease and at a low cost. Research on dynamic fracture in bio-inspired structures is very limited but it is crucial for the development of such materials with enhanced impact resistance.

In this thesis, we investigate damage in some bio-inspired structures through peridynamic modeling. We first print a 3D brick-mortar structure, 82% VeroClear plastic (a PMMA substitute in 3D printing; the stiff phase) and 18% TangoBlack rubber (a natural rubber substitute in 3D printing; the soft phase). We investigate damage in this 3D printed sample by low-velocity drop test with fixed and free boundary conditions. Under free boundary conditions, at this impact speed no damage was observed, while cracks form when the sample rests on a fixed metal table.

A 3D peridynamic model for dynamic brittle fracture is used to first validate it against the Kalthoff-Winkler experiment, in which a pre-notched steel plate is impacted at 32m/s by a cylindrical impactor and brittle cracks grow at a 70-degree angle with the impact direction. A new peridynamic model for a brick-mortar microstructure is created using the properties of PMMA and rubber. Because simulating the supporting table used in the experiments would be too costly, we choose to work with free boundary conditions and a higher impact speed (500m/s), to observe damage in the peridynamic model of the brick-mortar structure. Under these conditions, the damage is limited to the contacting brick only. The soft phase is able to limit its spread. Other boundary conditions are likely to cause wave reflections and reinforcements, which can damage other bricks, far from the impact point, as observed in our experiments.

Advisor: Florin Bobaru