The main aim of this project was to examine the effects of introducing hierarchy into honeycombs and determining the variables that preside over the global response of the structure. Specifically to understand how the in and out-of-plane elastic and non-linear plastic properties of honeycombs were affected by hierarchy. Analytical analysis of hierarchical honeycombs has been used to explain and predict the response of finite element simulations validated by experimental investigations. The early stage of the investigation focused on finding if the elastic modulus could be maintained or improved on an equal density basis due to the introduction of hierarchy. It is clear that honeycombs are sensitive to hierarchical sub-structures, particularly the fraction of mass shared between the super-and sub-structures. Introduction of an additional level of hierarchy without reducing performance is difficult, but was possible by functional grading. Another original result was that it was determined when the sub-structure could be assumed to be a continuum of the super-structure. Meaning the material properties from a single unit sub-cell could be used as the constituent material properties of the super-structure, as in previous work by (Lakes 1993) and (Carpinteri et al 2009) for example. Work investigating the in-plane, non-linear plastic response of hierarchical honeycombs showed that the introduction of hierarchy into honeycombs can have the effect of delaying the onset of elastic buckling, which is a common failure mechanism for low relative density structures. As such it was possible to achieve a marked increase in the recoverable energy absorbed by hierarchical honeycombs prior to elastic buckling or plastic yield. The potential benefits are less apparent in higher relative density structures due to the onset of plasticity becoming the first mode of failure. The out-of-plane properties also investigated showed no increase in the elastic properties due to the introduction of hierarchy, but showed a marked increase in the out-of-plane elastic buckling stress of 60% when compared to a conventional hexagonal honeycomb of the same relative density.

Nanoparticles can be used as building blocks of materials. Properties of such materials depend on the organization of the constituent particles. Thus, control over particle organization enables control over material properties. However, robust and scalable methods for arranging nanoparticles are still lacking. This dissertation explores the use of an externally applied magnetic field to organize magnetic nanoparticles into microstructures of desired shape. It extends to proofs of concept towards applications in material design and tissue engineering. First, external control over dipolar self-assembly of magnetic nanoparticles (MNPs) in a liquid dispersion is investigated experimentally. Scaling laws are derived to explain experimental observations, correlating process control variables to microstructure morphology. Implications of morphology on magnetic properties of such structures are then explored computationally. Specifically, a method is proposed wherein superparamangetic nanoparticles, having no residual magnetization, can be organized into anisotropic structures with remanence. Another application explores the use of magnetic forces in organizing human cells into three-dimensional (3D) structures of desired shape and size. When magnetized cells are held in place for several days, they are seen to form inter-cellular contacts and organize themselves into tight clusters. This provides a method for 3D tissue culture without the use of artificial scaffolding materials. Finally, a method to pattern heterogeneities in the stiffness of an elastomer is developed. This makes use of selective inhibition of the catalyst of crosslinking reactions by magnetite nanoparticles. The last chapter discusses future possibilities. / Ph. D.

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Composite materials offer a high strength-to-weight ratio and directional load bearing capabilities. Compression molding of composite materials yields a superior surface finish and good dimensional stability between component lots with faster processing compared to traditional manufacturing methods. This experimental compression molding capability was developed for the ME composites lab using unidirectional carbon fiber prepreg composites. A direct comparison was drawn between autoclave and compression molding methods to validate compression molding as an alternative manufacturing method in that lab. A method of manufacturing chopped fiber from existing unidirectional prepreg materials was developed and evaluated using destructive testing methods. The results from testing both the continuous and chopped fiber were incorporated into the design of a functionally graded hybrid continuous and chopped carbon fiber component, the manufacture of which resulted in zero waste prepreg material.