Single Crystal Plasticity (PRISM-PSAAP DOE) Understanding the behavior of materials at the nano/micron scale furnishes the basis required to develop theoretical models and reliable numerical tools for the prediction of the structural behavior of devices of interest in macroscopic applications. Continuum theories rest on the assumption that the relevant fields that describe the state of the material vary slowly at atomic scale.  Therefore, continuum theories break down in microscopic scale and fail to describe the relevant phenomena at this scale.   This is particularly important in today’s technological applications of materials and devices with micro and nanoscale features when the scale of the volume analysis approaches the microstructure and the continuum assumption diminishes.

Ultrafine grained materials (DOE-BES) Technological applications of materials and devices with nanoscale and microscale features commonly involve metals and alloys in their polycrystalline form. Plastic deformation in crystalline materials is carried by the nucleation and propagation of dislocations and the intricate structures they form. Grain boundaries interact strongly with dislocations and affect the mechanical properties; this is particularly important in samples with micro or sub-micron characteristic grain size when phenomena like grain sliding, grain boundary diffusion and migration as well as the interaction of dislocations with grain boundaries play a prominent role. Usually the response of polycrystalline materials is represented by means of an average over the grains, these representations are unable to capture the effects of the microstructure which is responsible for the unique mechanical properties of ultra fine grained materials such as the high yield and fracture strength and their dependency on the mean grain size. The purpose of this project is to develop a new plasticity theory to provide answers to the most basic questions about the role of grain boundaries in the deformation of ultra fine grained materials.

Nanowire heterostructures Nanowire heterostructures have their composition controlled. They are formed by creating junctions of different materials with interfaces perpendicular to the longitudinal axis. Due to their small radial dimension these junctions can be defect free even for systems with large lattice mismatch. We are using a continuum theory of defects and energy minimization  to estimate critical features  such as radius and critical mismatch.

Thin films (PRISM-PSAAP DOE) The continuing shrinking of dimensions and increased complexity in micron size devices, such as microelectronic interconnects and micro-electro-mechanical systems (MEMS) and several microdevices of broad interest in  communications, biology and medicine. The  necessity to meet new performance demands results in the emergence of new mechanical problems during manufacturing and operation. Understanding the behavior of materials at the nano/micron scale furnishes the basis required to develop theoretical and numerical models to predict the structural behavior of those micro-devices.

Molecular crystals (NSF) In pharmaceutical and food industries, materials are subjected to mechanical milling during manufacturing to reduce particle size. During this process mechanical stresses produce structural changes in the crystal lattice that often affect key properties of drug products, such as stability and dissolution rates. The theory and experiments conducted by Prof. Carvajal proposed in this project will provide information about the interaction of crystalline defects with surfaces due to the high surface to volume ratio in microscopic particles and will be a step toward the integration of microscopic mechanisms in the numerical modeling of crystalline materials in general.

Multiscale modeling of polymer composites (NSF - Boeing)

In order to predict the mechanical behavior of polymer nanocomposites it is essential to understand the mechanisms at the matrix CNT interface. It is of fundamental importance to accurately describe the effects of load transfer as well as damage produced by delamination in the interfacial region.


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