Reinforced rubber is one of the most important materials in modern life. It helps car and airplane tires withstand enormous stress, keeps industrial machinery running, and appears in everything from medical devices to garden hoses. Despite being used for nearly a century and supporting a global tire industry worth about $260 billion, scientists have never fully understood why it becomes so strong when mixed with carbon black particles. Now, researchers at the University of South Florida say they have finally solved the mystery. Led by engineering Professor David Simmons, the team uncovered how tiny carbon black particles transform soft rubber into a material capable of supporting massive loads, including fully loaded aircraft. Their findings were published in the journal Proceedings of the National Academy of Sciences . "How is it that we've been using this for 80, 90, 100 years and haven't really known how it works?" Simmons said. "It's been through enormous trial and error.…