Researchers simulate wear of materials as they rub together

An illustration of two different types of adhesive wear - asperity smoothing and fracture, dependent on the length of the microscopic nubs, or asperities - caused when two surfaces rub against one another. Forty years ago, MIT emeritus professor of mechanical engineering Ernest Rabinowicz calculated that 6 percent of the annual U.S. gross domestic product was lost through mechanical wear. His assertion gained enough traction that it became known as the "Rabinowicz Law." "Even so, the mechanism by which mechanical wear happens is one of the least understood areas of mechanics," said Derek Warner , associate professor in the School of Civil and Environmental Engineering. Given that dollar figure - 6 percent of today's GDP equals about $1 trillion - the ability to predict the behavior of tribological systems (tribology is the science of interacting surfaces in relative motion) as they degrade would benefit numerous industries and disciplines. And Warner, along with researchers from the École Polytechnique Fédérale de Lausanne, Switzerland, (EPFL) have proposed a way of doing just that. They have put forth a unified framework for simulating adhesive wear between materials with comparable hardness. The key factor is the size of the junctions between colliding asperities - microscopic nubs on what appear to be smooth surfaces - and their behavior when they exceed a certain critical size.