Engineer unwinding causes, solutions to bolt loosening

In 2011, one of America’s most advanced unmanned aerial vehicles crashed. In 2013, a train accident in Paris killed seven. And in 2016, a Union Pacific train derailed in Mosier, Oregon, spilling 42,000 gallons of crude oil.

Keegan Moore, assistant professor of mechanical and materials engineering, will use high speed cameras to capture the interface contact conditions — the surfaces the bolts hold together. Image credit:Craig Chandler | University Communication and Marketing

Those are just three dramatic examples of how one of the most vexing and little-understood phenomena of basic mechanics — the loosening of bolts over time — can create havoc. The University of Nebraska–Lincoln’s Keegan Moore is studying how that happens and how it might be prevented with a five-year, $727,410 grant from the National Science Foundation’s Faculty Early Career Development Program.

“Loose bolts aren’t just to blame for high-profile catastrophes; they’re a threat in everyday life, from playground equipment and cars to biomedical implants and the James Webb Space Telescope,” said Moore, assistant professor of mechanical and materials engineering.

Moore said that despite the ubiquity of bolts and screws in the infrastructure of all types, little is understood about how a structure’s dynamics can influence their loosening during normal operation.

“Bolt and joint loosening has been studied since the Industrial Revolution because it’s been a problem since then,” Moore said.

He’s hoping his research will answer some of those questions. He will focus on rotational loosening, which is caused by vibrations in structures.

Lock washers are the most common approach used to prevent bolts from loosening, but in many cases they’re ineffective or even increase the rate of loosening. Other approaches, including torque nuts and the use of two nuts on a bolt, seem to at best delay, not prevent, loosening.

Moore’s project will measure the interface contact conditions — the surfaces the bolt holds together — using high-speed digital cameras that film at thousands of frames per second. He believes the strains measured around the bolt head or nut can be mapped to the contact conditions inside the interface around the bolt hole. He also will produce modeling frameworks to reproduce the dynamics of loosening and determine how a structure’s dynamics influence loosening bolts.

“This will hopefully give us a new window to what’s going on in the interface that we’ve never had before and we’ll be able to measure how that changes dynamics as the bolt loosens and as the structure shakes,” Moore said.

One key challenge is understanding how one loosening bolt might have an impact elsewhere in a structure.

“Changes in one bolt can cause dramatic changes elsewhere … not just failure but changes in operation,” he said.

Loosening bolts is one aspect of America’s aging infrastructure. He hopes his research could lead to predictive maintenance that would focus on specific likely problem areas, which is more efficient than trying to monitor all bolts.

As with all CAREER grants, Moore’s includes an education component. He plans to “gamify” existing dynamics courses in mechanical engineering by developing collaborative, not competitive, game-based learning and create a virtual reality dynamics laboratory “to generate excitement and curiosity in the classroom and transform the sharing of ideas.” He also plans to create a new graduate course on game-based learning.

NSF CAREER awards support pre-tenure faculty who exemplify teacher-scholars’ role through outstanding research, excellent education and the integration of education and research.

Source: University of Nebraska-Lincoln

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