CAREER: An Experimentally-Informed Multi-Level Framework for Modeling Fracture of Hexagonal Metals

University Of New Hampshire, Durham NH

Investigators

Abstract

Metals and alloys with a hexagonal close-packed structure have potential applications as lightweight structural materials, particularly in future automobile applications. Improving fuel efficiency by introducing fracture-resistant lightweight structures in air and ground transportation will lower operating temperatures, lengthen component life, and reduce greenhouse gas emissions. These metals also address design challenges instrumental to lighter and thinner consumer electronics. One factor limiting wide adoption of these materials is their tendency to fracture during processing. Much remains to be learned about how and why this fracture takes place, and how to mitigate it to allow cost- and energy-efficient use of these materials for manufacturing. A better understanding of the fracture mechanisms, and the creation of a reliable computational toolset for predicting fracture, can enable effective design of damage-tolerant metals and the certification of materials as well as new processes using computational methods rather than trial-and-error experimental approaches. This Faculty Early Career Development (CAREER) Program award supports research to advance the understanding of fracture in hexagonal close-packed metals and to advance microstructure-based predictive modeling. New understanding about the behavior of industry-relevant lightweight titanium and magnesium alloys will result. Undergraduate and graduate students will be trained in materials characterization, testing, analytics, modeling, and simulation methods to advance the fields of materials science and mechanics. The skills will prepare the students to pursue careers that contribute to U.S. competitiveness. Unlike continuum fracture mechanics, which assumes that a void initially exists, the models created here will be sensitive to when and where fracture originates, particularly at grain boundaries. Pure hexagonal metals will be used to establish resistance of grain boundaries to nucleate voids during plastic deformation. Void nucleation sites will be linked to 3D structural features via in-situ loading within a focused ion beam scanning electron microscope in combination with electron backscattered diffraction imaging, in-situ testing and imaging using near-field high-energy X-ray diffraction microscopy, and micro X-ray computed tomography. The compiled comprehensive statistical database of structures and void nucleation events will inform meso-scale crystal plasticity models that can represent the crystallography and spatial physical state of microstructure and the cohesive strength of grain boundaries to predict plasticity and fracture. Finally, a novel multi-level toolset will be created to link the meso-scale physics of deformation and void evolution for predicting fracture at the macro-scale in a computationally tractable manner to facilitate simulations of material behavior during manufacturing and in service conditions. The toolset will provide the physical basis and pathway towards a longer-term vision of designing materials based on prescribed performances.