Alan D. Roberts sent shockwaves through the rubber industry in general and in the field of contact mechanics in particular when he and two colleagues devised what is now known as the JKR Equation.
In short, Roberts—the “R” in the acronym that names the equation—helped to formulate the theory of adhesive contact between two elastic bodies, utilizing a balance between stored elastic energy and loss in surface energy.
The method to studying adhesion and friction, first published in 1971, has become one of the most widely used devices for research on surfaces and interfaces.
But Roberts, the 2014 Charles Goodyear Medalist, may have made his greatest contribution to his field with his work on a product that helped to withstand shockwaves on a much grander scale.
During his four-decade-long career at England's Malaysian Rubber Research Association—now called the Tun Abdul Razak Research Center—Roberts and his fellow scientists helped to develop building mounts that would isolate vibrations, particularly those caused from earthquakes.
The technology was perfected in the early 1970s, and a decade later one of the laboratory's first earthquake bearings was installed on a government building in San Bernardino, Calif.
“That was a real ... I was going to say a real hit, but it prevented the hit from tremors,” Roberts said, “and we were able to show it did a wonderful isolation job compared to other buildings in San Bernardino.”
The building withstood an earthquake, Roberts said, better than a local hospital “that suffered rather badly. One doesn't wish to have comparators like that.”
Latest award winner
Helping to further inventions such as the building mounts is precisely why the 73-year-old Roberts received the Charles Goodyear Medal, the ACS Rubber Division's most prestigious award, during the Rubber Division's 185th Technical Meeting and Educational Symposium in Louisville, Ky., in March.
The award honors someone for outstanding innovation, invention or development that resulted in significant change or contribution to the nature of the rubber industry.
The building mount illustrates how research in one area often leads to a breakthrough in another.
Roberts said the building mount evolved from previous work done by the laboratory on bridge bearings. It was work done at the MRRA lab that led to the installation of the first bearing on a bridge in England in 1957.
“I think, justifiably, we can be proud of that,” said Roberts, who co-authored the book, “From Pelham to Penang—Natural Rubber Bearings for Civil Engineering,” to mark the completion of the 24-kilometer Penang bridge in Malaysia that was built using the lab's rubber bearing technology.
The bridge mount technology led to research on mounts. The lab was looking to find technology that would deaden vibrations emanating from London's sophisticated underground system.
Roberts said they combined rubber, metal and steel to create isolators “to deaden the noise (on) buildings from vibrations. And so that was really quite significant.”
He said the first building mounts, as scientists called them, were installed in a building in central London in 1964. Researchers then extended the idea to developing building mounts that would isolate earthquake tremors.
“One of the problems is, when the ground moves, the vibration displaces, so the bearing, to cope with it, has got to be able to shift and hold onto plane considerably,” Roberts said. “You don't want it to overshear; otherwise the thing would topple. The approach we used to prevent overshear was to stiffen the rubber, to give the rubber certain viscoelastic properties.”
Days at Cambridge
Roberts' research in rubber physics dates back to his days in the early 1960s as a student working on his doctorate at the University of Cambridge. “You get drawn forward,” he said. “Questions arise, and you just need to find answers, which means reading books and asking people.”
He and a group of other students studied different aspects of friction, lubrication and wear, analyzing all kinds of materials, including rubber, metal, glass, ceramics and other polymers.
His mentor, Cambridge professor David Tabor, a scientist renowned for work in friction and lubrication in his own right, received funding from a wiper blade company that wanted to improve its products.
“One had to learn quite a bit about rubber in order to make some progress,” he said. “You get drawn forward. Questions arise, and you just need to find answers, which means reading books and asking people.”
Roberts' research focused on what occurs when the rubber meets the windshield. The edge of the wiper blade is extremely fine—a fraction of a millimeter, he said—and when bits of grit come in contact with the blade, cuts develop in the rubber, causing streaks on the glass.
“If we could understand what goes on where the rubber meets the glass, wet or dry,” he said, “then it would help them to perhaps come up with a better design.”
Roberts, however, was perplexed, when he attempted to analyze the point of contact between the rubber and glass when water was applied to the glass.
“You look through (the glass), you could see beautiful dry contact patches, no problem,” Roberts said. “Put water on it, everything vanished. It really took me months to understand.”
He continued his research for a few months at Bell Laboratory in Murray Hill, N.J., working with scientist Jeff Courtney-Pratt, whom he called an “optical expert.”
“When you shine a light beam through a sheet of glass, you get a reflection from the top side. I was interested in what was going on the bottom side where I pressed the bit of rubber.”
When he returned to England a few months later in 1966, Roberts found his answer. The solution dealt with the optical contrast. “It suddenly hit me,” he said. “That's when I had the "Eureka moment.' “
Once he received his doctorate from Cambridge, Roberts agreed to continue research at the university. Soon thereafter, he and K.L. Johnson began work on metal friction at another Cambridge lab.
Four decades of research
In 1974, an opportunity arose for Roberts to continue his work at the MRRA, where he would focus exclusively on rubber friction with scientist Adolf Schallamach, the 1982 Charles Goodyear Medalist known for his research on the mechanisms of tire traction, abrasion and wear.
“He asked, "Would you like to come here? We could offer you a position as senior scientist. That was quite nice. But if you could take a little less money, I would be prepared, provided I can get it through the board, to offer you a position of principal scientist,' “ Roberts recalled. “That was a knockout blow. You couldn't turn that down.”
The British Rubber Producers' Research Association, as it was initially named, opened near Hertford, England, in 1938 as a sister laboratory to one established in Malaysia in 1925, whose mission was to research the cultivation of rubber trees and extract the highest quality latex.
During his career, Roberts investigated the sliding friction of rubber on ice and wet surfaces, showing the effects of pH and salt concentration. He continues that work today.
In 1998, Roberts received the Lavoisier Medal of the French Society of the chemical industry. He has written 105 published papers. According to the Rubber Division, his work has impacted such areas as tires on wet and dry roads; windshield wipers; and rubber seals and other rubber products.
Roberts retired in 2005, but he continues to use the renamed facility for his research. “Like all these things, one thinks one will move on,” he said.
“But the continuing moments with colleagues, collaborators around the world, I thought the reason I stayed for a career that I did was that the atmosphere was so pleasant.”
Roberts said he was destined for a career in rubber.
“I wasn't fit for any other profession but the rubber industry, in spite of interesting work on metal friction,” he said. “I quite liked the blend of a bit of physics and a bit of chemistry and a bit of guesswork.”