Of particular interest in this project are the mechanical properties of metals in systems that consist of structural components whose dimensions, or the dimensions of their substructure, lie in the range of tens of nanometers to tens of micrometers. The investigators will develop experiments, models and computational platforms to pursue reliable mechanical properties and prepare maps for use in the design and analysis of such systems. Innovations include advancements in bulge testing techniques for studying submicron structures, advancements in multiscale modeling based on molecular dynamics and dislocation dynamics analyses, and development of a crystal plasticity hardening law for submicron elements.
The potential performance levels of miniaturized systems made of submicron components, such as microelectormechanical systems and lightweight metal panels for automotive and aerospace application, can lead to new performance level and energy efficiency not achievable with current materials. The outcome of this project would have major impact on these emerging technologies by providing scientific bases for designing of such systems. Additionally, this project will involve graduate and undergraduate students in mentoring primary and secondary school students through a unique outreach program. The goal is to increase students' interest in science and engineering, broaden the background of doctoral students in outreach activities, and address issues of disparity that may be underlying concerns in attracting women and minorities to doctoral research.
Within the field of materials engineering, a long-running goal is to be able to design new metals and alloys. Computer simulations of small groups of atoms can predict the performance of a material, but scaling up the predictions to real volumes of materials is an ongoing problem. Rather than using ever-larger and more expensive super computers to try and simulate a slightly larger volume, the multi-scale approach relies on passing information from a small simulation to a larger simulation, and then passing that information up to yet another simulation of a larger volume. Similarly, experiments of bulk materials can measure properties, and smaller and smaller tests can be carried out. This project set out to demonstrate measurements and computational simulations of materials that match on a length scale that matches. The length scales of interest on this work are the atomistic, the dislocation sale (a dislocation is a defect responsible for permanent deformation in metals), and on the grain scale (real metals are made up of small grains, much like a snowball is made of snowflakes). The simulations used were molecular dynamics (for atomistic), information from this is passed to describe the motion of dislocations in dislocation dynamics, and then the performance of a crystal with dislocations is passed to plasticity models of the grains. At the same time, experiments using nanoindentation and thin film testing were carried out on a wide range of metals. One critical feature that arose was how to address the variation in real materials. The smaller the simulation or test, the more likely we get a "perfect" result; however real systems often fail not by the perfect areas but by deformation around local weak spots and defects. The key feature of the results published in this series of papers generated by this work focused on describing deformation in metals in statistically relevant ways. It was shown that one can directly compare experiments and models that don’t just match "average", or "maximum" results, but that you can develop methods that describe the entire distribution of measurements. And by predicting and verifying distributions of properties, the ability to quantify uncertainty in future designs is improved. Students involved in this research project were mentored in developing methods to explain science and engineering results to broad groups of younger students. The students developed a week-long series of activities, following best practices developed in other NSF funded projects such as the University of Wisconsin’s MRSEC program, for a grades 7-12 "science camp" at Washington State University. After this development, the students continued to refine the topics to reach students in shorter "Science Day" activities to get students that couldn’t spend a week exposed to concepts of strength in materials. Finally, in the latter years of the projects, the graduate students worked on making elementary atomistic model kits for elementary grade students so they could make "crystals" to take home from the one day events. In total, the graduate students presented and worked with over 90 students, and gained a significant amount of experience in learning how to present complex topics to young students in an engaging manner.
