CAREER: In-situ Advancements for Study of Multi-axial Micromechanics of Solid Materials

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This Faculty Early Career Development (CAREER) Program grant supports research on the mechanics of the microscale level deformation of metals through advanced experimental mechanics and analysis. The research contributes to national Materials Genome and Advanced Manufacturing Initiatives. Microstructure-property relationships are central to the understanding of the mechanical response of materials. For solid materials, such models require knowledge of how microstructural building blocks - their grains - respond to thermo-mechanical load changes. New insights into these processes will be gained through novel in-situ X-ray diffraction experiments. X-rays will penetrate materials while thermo-mechanical loads are changed. Measuring changes in X-rays diffracted from samples will provide quantifiable information about changes of the grain structures. A novel class of in-situ experiments is considered where two-dimensional thermo-mechanical loads are applied in-situ. The sharing of the unique experimental data will enable other researchers to test their multi-axial, thermo-mechanical, process-microstructure-property relationships. The present research methodologies will be incorporated into a new Nonlinear Solid Mechanics graduate course. An annual international design competition using advanced solid materials will be initiated through a professional engineering society. Graduate students will be trained to perform outreach at area high schools, community colleges, and libraries by presenting advanced material and in-situ experiment capabilities in a format that stimulates imagination and demonstrates accessibility. A non-destructive, combined planar-biaxial and induction heating in-situ X-ray diffraction experiment will be developed. It will be employed along with new data analysis methodology for studying concurrent phase transformation, elasticity, and plasticity of individual grains within a thermo-mechanically loaded polycrystalline specimen. The new experiment will be used to explore uncharted territory in the micromechanics phase transformation in shape memory alloys and stainless steels. Since the roles of individual deformation mechanisms within crystals and individual crystals within polycrystals will be quantified, bridges between different scales of mechanics will be elucidated. The following research questions are considered: (1)How do inter-granular boundary conditions give rise to stress distributions amongst microstructures? (2) What are the interaction energies required to activate different transformation, twinning, and slip systems at the crystal scale, and how do microstructural constraints affect them? (3) What is the proper microstructural building block for micromechanical modeling of martensite? (4) How do we measure elastic anisotropy of low symmetry martensite structures? (5) Why is hysteresis different in thermal vs. stress-induced transformation of shape memory alloys, why does it vary with loading mode, and does processing anisotropy change the nature of transformation hysteresis with respect to different material axes?