GOALI/Collaborative Research: Strain Gadient Plasticity Modeling to Link Microstructural Non-Local Effects of Dislocation/Interface Interactions with Ductility and Springback

Brigham Young University, Provo UT

Investigators

Abstract

A key component in the strategy to lightweight vehicles for reducing harmful emissions involves the introduction of advanced light alloys across a wide spectrum of vehicle components. However, advanced alloys are typically less ductile than their heavier predecessors and are liable to fracture during the shaping and forming operations. On the other hand, various empirical observations have demonstrated that careful selection of strain (deformation) path during the forming process can significantly delay component failure. Current simulation frameworks do not account for key phenomena at the microstructural level needed to analyze and design better forming processes and to guide alloy selection and development for optimal exploitation of current and forthcoming lightweight materials. By combining novel developments in microscopy and modeling, the critical issue to be explored in this Grant Opportunities for Academic Liaison with Industry (GOALI) research project involves interactions between mobile planes of atoms (dislocations) that facilitate shape change of the component, and microstructural interfaces, such as precipitates and grain boundaries. Barriers to dislocation glide cause atomic pileups, and related backstress effects, that are not considered in traditional models, but can potentially be manipulated to improve overall ductility via careful design of strain paths that occur during forming. The research will be integrated into industrial practice by the industrial partner, Aleris, to deliver potentially transformational capabilities in vehicle lightweighting efforts. As a result of this collaboration, the students involved will also gain an understanding of industrial challenges and drivers. Knowledge derived from the research will be integrated into course curricula for graduate and undergraduate students, while a cloud-based App hosting the developed model will be made available to the broader research community via Materials Resources, LLC. This interdisciplinary project, involving the complementary expertise of two universities and an industrial partner, is driven by the hypothesis that accurate calculation of strain gradients, and related backstress and localization fields, during forming can be used to design strain paths that optimize material ductility, effectively delaying localization/failure in high-strength aluminum (Al) alloy sheets. The team will conceive and implement a novel strain-gradient crystal plasticity finite element model to encapsulate the scientific insights. The model will be guided by a combination of two cutting-edge microstructural techniques that will provide unprecedented detail of the deformation behavior at the relevant length-scale. High-resolution electron backscatter diffraction (HREBSD) will be employed for mapping both geometrically necessary dislocations, accompanying strain gradients, and related backstress for each strain path, while high-resolution digital image correlation (HRDIC) will extract the plastic strain tensor for a complete picture of the deformation. The scientific advances will be applied to warm forming of two high strength alloys with different microstructures, namely AA6022-T4 and AA7050-T6. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.