Engineering professor made Auburn the place to study fracture mechanics

January 10, 2020 @ 9:05 a.m.

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Hareesh Tippur likes to ask why and how.

Why do materials bend? Why do they break? How do structures fail?

Failure of materials and structures is inevitable as they all contain invisible defects. That’s what keeps Tippur fascinated with fracture mechanics—the science of studying objects containing cracks—at Auburn University.

Tippur, the McWane Professor of Mechanical Engineering and associate chair for graduate studies in the Samuel Ginn College of Engineering, is one of this year’s two recipients of the university’s Faculty Award for Creative Research and Scholarship. The honor acknowledges the research achievements and contributions of faculty who have distinguished themselves through research, scholarly works and creative contributions to their fields.

It may seem odd to hear that anyone studies failure, but everyone should be glad someone does.

Take for instance, an airplane. The impact from a pebble or tool drop takes micro seconds to cause a miniscule crack in a fuselage, but it may not produce significant visible damage until the airplane is racing down the runway at 170 mph or flying at 30,000 feet. Tippur wants to understand the safety of that fuselage.

Fracture mechanics is all about understanding why engineering materials, such as carbon fiber reinforced composite or aluminum, fail, how they fail and how to prevent such failures.

Tippur said fracture prevention is the ultimate goal, but one must first understand the material’s behavior—how, when and why something bends, breaks or fails.

Rather than manufacturing airplanes with aluminum, carbon fiber reinforced composites are increasingly used because they are half the weight and twice as strong as aluminum.

“Therefore, it’s not just aluminum anymore. The new airplane structures contain over 50 percent composite materials. What is a composite material? Microscopically it is mats of carbon fibers and glued with epoxy that you use to fix things around your house,” said Tippur. “That’s basically it.”

Composite materials are inherently complex in terms of microstructure and catastrophic failures are possible, if the design is poor.

“In order for you to design it very well, you need to understand the fracture mechanics of such materials very well,” he said.

Engineering from the start

Growing up in India, Tippur was likely destined for a career in engineering. The son of a civil engineer, he was initially fascinated with civil structures and then airplanes. His plan was to get an advanced degree and do research at an aerospace or defense industry in his native country.

It is during his thesis research at the prestigious Indian Institute of Science, Tippur developed his fascination with structural failure. With an advanced degree, Tippur spent about a year working at one of India’s defense research and development labs. The experience wasn’t what he had expected, so his advisor suggested he go to the United States for a doctoral degree.

The advisor had done so, eventually returning to India to teach future engineers and perhaps Tippur could do the same.

At the State University of New York-Stony Brook, Tippur continued to focus on why and how structural materials fail. He learned to use lasers and light to make sophisticated measurement and study fractures in materials. He couldn’t solve the problem then, let alone today.

No one can.

A ‘one-size-fits-all’ solution to the problem has evaded researchers because structural materials continue to advance. As long as new materials are produced and totted for particular qualities, there can only be specific answers to why it would inevitably fail.

Take automobiles, for instance. Steel was primarily used for decades because it was structurally strong, but then lighter materials like aluminum, composites and plastic came along, making automobiles lighter and more fuel efficient. This trend is bound to continue.

Tippur said today’s challenge is to create materials that meet multiple requirements, such as lightweight, strong, tough yet sustainable and reusable. A material that “checks all these boxes” is a long, long, long-term goal of materials engineers, he said.

Studying Behavior

After SUNY, Tippur was did post-doc work at Caltech, where he devised optical tools to measure high speed fracture events.

“Materials behave very differently in slow and fast loading events, like squeezing a wad of silly putty or bouncing it off the floor,” he said. “How fractures occur at high speeds therefore aren’t like the slow speed ones.

“The human eye can see a slow loading event, but a fast one, like cracking of a glass window, happens too quickly for humans to perceive.”

Tippur uses light and high-speed photography to capture what we can’t see.

“The latest camera we have here records events at 5 million frames per second. It’s hard to convince people we can do that,” he admitted. “But it is necessary because fracture events during projectile impact, shock and blast happen extremely fast, like mile-a-second speed crack growth occurs in glass when impacted. For me to understand the full spectrum of material behavior, I need to understand what happens at very high speeds and at small scales.”

Tippur came to Auburn in 1990. He liked the proximity to NASA Marshall Space Flight Center in Huntsville and the fact that no one was studying fracture mechanics on the Plains.

“I thought I could contribute something new at Auburn,” he said.

And he has.

“Now any time fracture mechanics, particularly high-speed fractures, come to anybody’s mind, they think of Auburn, and hopefully me,” Tippur said.

Certainly Tippur has had opportunities to teach and conduct research elsewhere over the past 29 years, but there are some significant factors that have kept him here.

“I am fortunate to have attracted many good students over the years. I have also been successful in gathering resources to build cutting-edge facilities here,” he admitted. “If not, I would have looked elsewhere.”

Tippur said he maintains high standards for his undergraduate and graduate students and strives to be a good mentor to them.

“Any student who walks into my lab knows they are signing up for something interesting, unique, but at the same time, very challenging,” he said.

To Tippur, earning the Faculty Award is a testament to his students and the work they produce together. Many of his students go on to work at national labs, Fortune 500 companies or academia because of Tippur and an Auburn Engineering education.

“It makes this job quite satisfying to hear their success stories,” he said. “I’m still full of ideas, so as long as there are resources and the school keeps encouraging me to do what I am good at, I’ll keep plugging away.”

BY AMY WEAVER

Hareesh Tippur, the McWane Professor of Mechanical Engineering and associate chair for graduate studies in the Samuel Ginn College of Engineering

 

 

Categories: Engineering


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