Anthony M. Waas
Fulton Professor of Aerospace and Mechanical Engineering
Director, School for Engineering of Matter, Transport and Energy
Fulton School of Engineering
Arizona State University
Presentation Title: The Effects of Favorable Geometric Perturbations in Controlling the Collapse Response of Thin-walled Shell Structures
Abstract: This work investigates how favorable geometric perturbations can be leveraged to control the collapse response of thin-walled shells—structural elements widely utilized in aerospace, civil, and naval engineering. The study considers thin-walled cylindrical shells under axial compression and spherical shells exposed to external pressure. It is well established that geometric imperfections—or unfavorable geometric perturbations—can dramatically reduce the collapse strength of these structures. Due to the inherent instability in their postbuckling response, structural designers traditionally resort to knock-down factors, limiting maximum allowable loads to ensure safety.
However, this conservative approach raises a pertinent design question: Can intentionally introduced favorable geometric perturbations yield shells with more predictable, controllable deformation paths and with less variability in their maximum collapse pressure? For spherical shells, our studies demonstrate that introducing outward-pointing (rather than inward) dimple perturbations can enhance collapse resistance under external pressure, designating these as favorable configurations. In the context of cylindrical shells, the postbuckling reserve capacity known from plate structural mechanics is exploited: polygonal prismatic shells (plate-shells) are proposed and analyzed, combining both plate-like and shell-like characteristics. The results show that these plate-shells exhibit relative insensitivity to geometric imperfections over a range of designs and sustain collapse loads that exceed those of conventional circular cylindrical shells.
These findings represent a significant shift from the commonly reported imperfection sensitivity dominating the collapse behavior of spherical shells under external pressure and axially compressed cylindrical shells. The research suggests a pathway towards designing shell structures with more robust, predictable collapse responses, which could influence future standards and safety margins in engineering practice.
Biography: Anthony M. Waas, Fulton Professor of Aerospace and Mechanical Engineering is the Director of the School of Engineering for Matter, Transport, and Energy (SEMTE) at Arizona State University. SEMTE encompasses the Aerospace, Mechanical, Materials, Bio, and Chemical Engineering programs. His current research robotically manufactured lightweight thin-walled structures—including in-space fabricated structures—computational modeling of composite aerostructures, damage tolerance of composites, affordable textile composites, hydrogen storage for mobility, and data science applications in materials and structural modeling.
Professor Waas served as the Felix Pawlowski Collegiate Chair and Department Chair, Professor of Aerospace Engineering, and Director of the Composite Structures Laboratory at the University of Michigan from 1988 to 2014. In January 2015, he joined the University of Washington as Chair of the Aeronautics Department and the William Boeing Endowed Professor. He is a Fellow of the American Institute of Aeronautics and Astronautics (AIAA), American Society of Mechanical Engineers (ASME), American Society for Composites (ASC), American Academy of Mechanics (AAM), and the Royal Aeronautical Society, UK.
He has received numerous awards including multiple best paper honors, the 2016 AIAA/ASME SDM National Award, the AAM Junior Research National Award, and the ASC Outstanding Researcher International Award. In 2017, he was honored with the AIAA-ASME-ASC James H. Starnes Jr. Award for seminal contributions to composite structures and materials, as well as for mentoring students and young professionals. Professor Waas was elected to the Washington State Academy of Sciences in 2017 and to the European Academy of Sciences and Arts in 2018.
Further distinctions include the AIAA ICME Prize (2020), ASME Warner T. Koiter Medal (2020), the AIAA Dryden Lecture in Research, and membership on the US National Academy of Engineering’s Aeronautics and Space Engineering Board since 2021. Most recently, he received the CT Sun Medal from the American Society of Composites in September 2023 and the 2025 ASCE Raymond D. Mindlin Medal recognizing his lifelong contributions to aerospace composite structures.