Shattered Rim Wheel Defects and the Effect of Lateral Loads and Brake Heating on Their Growth

Abstract

This report details studies conducted by Transportation Technology Center, Inc. (TTCI), a subsidiary of the Association of American Railroads (AAR), to determine the causes and behavior of shattered rim defects in wheels. Shattered rim defects are the result of large fatigue cracks that propagate roughly parallel to the wheel tread surface. They form and grow 1/2 to 3/4 inch (12–20 mm) below the tread surface. Once a shattered rim crack is formed it will grow under normal rolling loads. Therefore, the prevention of shattered rims is best accomplished by preventing crack initiation. Shattered rims tend to occur in either relatively new wheels or those that are near their condemning limit. Recent changes have been made to ultrasonic test requirements in AAR Specification M-107/208, “Wheels, Carbon Steel,” to reduce the acceptable size of discontinuities. This will help reduce the occurrence of some shattered rims, but will not prevent the formation of all of them. Ultrasonic testing of returned wheels would be effective in reducing the incidence of shattered rims in wheels with thinner rims.