| dc.description.abstract | This dissertation studies mechanical behavior, damage, and fracture of a silicone elastomer, elastomer composites, and a natural composite (bioenergy sweet sorghum). First, we identify and investigate a peculiar form of fracture that occurs in a highly stretchable silicone elastomer. We find that under certain conditions, cracks propagate in a direction perpendicular to the initial precut and in the direction of the applied load. Due to the crack tip deflection, the material ahead of the crack front continues to sustain load, thereby enabling enormous stretchabilities.
This dissertation then investigates fracture behavior in a new type of elastomer composite. Unlike in standard reinforced composite systems, we dispersed voids into a silicone elastomer matrix. One design implements interconnected rectangular prisms of voids and another incorporates randomly distributed spherical voids. This work demonstrates that the void-embedded silicone elastomer provides increased rupture resistance, flaw tolerance, and stretchability, while simultaneously decreasing the overall weight.
We also conduct finite element analysis (FEA) of flexible and stretchable electronics that have complex composite structures. First, we perform FEA simulations of stretchable ultrasound sensor arrays. This simulation provides stress distributions of these devices under biaxial tension and provides insights into limitations in terms of stretchability. Next we perform simulations of flexible photovoltaic devices to design optimal thicknesses of the composite, as to maximize its flexibility. Finally, we study a topic in optoelectronics aimed at controlling the activity of subsets of neurons and nerve fibers in vivo. These three simulations provide visualized stress distribution of complex composite structures and their limitations in terms of stretchabilities and flexibilities.
Finally, this dissertation investigates the mechanical response of a natural composite: a bioenergy crop (Sorghum bicolor (L.) Moench). The goal is to determine whether time-dependent effects are prevalent in this material, and if so, to provide insight into potential ramifications in terms of structural stability during growth. To do so, we implemented experimental measurements of time/rate dependency of piths and stems of sorghum under compression. These measurements demonstrate that sorghum is not a simple reversible elastic material and provide fundamental information to understand structural failure and mechanical stability of grass stems.
Mechanical and fracture behaviors of elastomers, elastomer composites, and natural composites are complex and often even unintuitive due to their unique properties stemming from their complicated micro- and macro-scale geometries. This dissertation provides experimental data and FEA simulations that offer fundamental insight into mechanical and fracture behavior of elastomers, elastomer composites, and natural composites. | en |
