Rethinking aerospace structures: SEMTE Director Tony Waas opens SSDM 2026

The ASME Aerospace Structures, Structural Dynamics, and Materials Conference, known as SSDM, brings together researchers from academia, industry and government to share advances in structural engineering, materials and aerospace research.

This year’s conference, held in Long Beach, California, featured four plenary speakers highlighting important areas of research within the aerospace community. Among the invited speakers was Anthony Waas, professor and director of the School for Engineering of Matter, Transport and Energy, who delivered the opening plenary lecture, “The Effects of Favorable Geometric Perturbations in Controlling the Collapse Response of Thin-walled Structures.”

Waas’ presentation explored a new approach to improving both the stability and predictability of thin-walled shell structures by rethinking their geometry.

The problem with cylindrical structures

Thin-walled shell structures are found everywhere, from rocket bodies and storage tanks to soda cans. Their lightweight design allows them to carry substantial loads while minimizing weight, making them an ideal choice for aerospace applications. However, despite their widespread use, these structures have challenged engineers for decades because of one flaw: they can buckle unexpectedly under compression.

Because engineers cannot accurately predict when a cylindrical shell will collapse, designers apply knockdown factors to reduce the total design load. This factor determines what percentage of the ideal load can safely be applied to the structure. While this approach has proven effective, it also results in heavier structures, which reduces payload capacity, fuel efficiency and overall performance.

A more predictable geometry

Rather than trying to better predict the behavior of traditional shells, Waas proposed changing the geometry of the shell itself.

Through collaboration with students and researchers, Waas developed a polygonal shell, constructed from a series of flat panels joined together instead of a smooth cylindrical shape. As the number of panels increases, the structure increasingly resembles a cylinder while responding much more consistently under compressive loading. This greater predictability is central to the concept.

“When you have an increased predictability capacity, your structural design tends to be much better,” Waas says.

The research team validated the concept through computational modeling and laboratory experimentation, including compression tests on 3D-printed polygonal shells. By measuring deformation and load-carrying capacity, the researchers demonstrated that polygonal shells behaved more consistently than cylindrical shells.

“If I take a circular shell and a polygonal shell of the same diameter, the amazing thing is that I can accurately predict the behavior of the polygonal shell, but not the circular shell,” Waas says. “That’s exactly what you want in structural engineering.”

This improved predictability has important implications for aerospace design. By reducing uncertainties in structural behavior, engineers can rely less on conservative knockdown factors and design lighter structures without sacrificing safety. In aerospace applications, reducing structural weight can allow for heavier payloads and improve fuel efficiency.

Taking polygonal shells further

Waas also sees opportunities to take this concept even further. By reinforcing the edges where adjacent panels meet inside these polygonal shells, engineers can create stiffened shells that provide additional axial stiffness while preserving the predictability of polygonal geometry.

To date, Waas and his team have focused primarily on creating these polygonal shells from monolithic materials, like aluminum and 3D-printed polymers. The next step is to extend the concept to fiber-reinforced composite materials, which are used in modern aircraft and spacecraft for their exceptional strength-to-weight ratio. Composite structures add more design variables due to their complexity, which creates a larger design space to explore and optimize.

Those additional variables also create an opportunity to use computational tools to accelerate the design process.

As structural optimization becomes a more widespread research field, Waas believes machine learning and artificial intelligence could play an increasingly important role.

“When the design space becomes very broad, the number of variables increases,” Waas says, “That’s when AI and machine learning become very useful at parsing data. When you’re considering so many thousands of different combinations, they are useful tools to have.”

Ultimately, Waas hopes polygonal shells will move beyond the research stage.

“My goal is that polygonal shells will be used in the design of rockets, spacecraft and aeronautical applications,” Waas says.