By Rachel Riley
A shelf in Douglas Holmes’ Boston University office is filled with brightly colored toys resembling what you might find in a bag of party favors passed out at a seven-year-old’s birthday celebration—not the tools in a mechanical engineer’s workplace.
But many of the knickknacks—the coiled metal Slinky, the miniature egg-shaped canister of Silly Putty, the rolled up cloth snap bracelet—have an important characteristic in common that often guides the research at Holmes’ Mechanics of Slender Structures (MOSS) Lab at BU.
They all change shape dramatically with relatively little effort.
“Our work focuses on understanding and controlling how objects change shape,” said Holmes (ME, MSE), who began teaching at BU’s College of Engineering in 2014. “We spend a lot of time trying to think of ways we can get large shape changes for small amounts of energy input.”
Holmes’ research at the MOSS Lab focuses primarily on how materials change shape when certain forces are applied and how the structure or geometry of an object can be used to reproduce the same outcomes in different materials.
For example, silicone can be used to produce a small rounded cap that pops inside out when a tiny amount of force is applied, Holmes said. The math used to create the rubber cap can be used to manufacture a steel cap in the same shape that functions similarly.
“What we’re trying to do is come up with a general framework,” he said. “When you study the way objects change shape, you want to identify a process that works with multiple materials. The idea is to bring the materials and the geometry together.”
Holmes and his students are exploring another interesting area of structural mechanics at the MOSS Lab: growth-activated manufacturing, or designing structures so that they are able to transform their shape in an instant, making the production process quicker and easier.
“We’re trying to grow basic shapes into complex structures,” he said. “We’re laying the groundwork for adaptable structures that can morph on demand. This may have applications ranging from 3D printing to soft robotics.”
Structure and geometry of materials were not always Holmes’ specialty, he said.
He earned his undergraduate in chemistry from the University of New Hampshire, where he worked in a lab with polymer scientists experimenting with formulas for latex paint and how different additives can cause the paint particles to take different shapes. This was his first experience with soft materials such as rubbers, plastics, and fabrics—all of which would become integral to his research today.
“I’ve meandered pretty far from where I started,” He said. “It took me a long time to get to the core of what I’m interested in.”
After receiving his master’s degree and Ph.D. at UMass Amherst in Polymer Science and Engineering, Holmes completed a postdoctoral research fellowship at Princeton University and later worked as an Assistant Professor at Virginia Tech.
“Teaching is how I learn,” he said. “To me it’s a really fulfilling part of the job. It keeps me grounded and forces me to seek better explanations, better visual tools, and better communication techniques. That helps in the classroom, but it also helps with my research.”
Holmes said the biggest challenge in his research is choosing the questions that deserve the most attention from him and his students.
“I’m always pushing my students to look for interesting things, things that are really curiosity-driven, inquiry-driven,” he said. “We want to be thinking very broadly. That challenge to think broadly and deeply at the same time, it’s always difficult for me.”