Stresses in a 33-inch (.840 m) railroad car wheel in response to static rail loadings are presented on the basis of experimental work and theoretical predictions. In regions away from the contact area, the theoretical predictions are verified by experiment. The rail load stresses are compared to theoretically damaging thermal loads, and a possible method of analysis of fatigue damage from the combined loading is discussed.

Field tests were conducted to verify and gather additional information concerning interior wheel temperatures, hot spot temperatures on wheel treads, braking forces, and coefficients of friction during actual service type braking with different types of brake shoes. The tests were conducted with either constant brake shoe loads or constant braking horsepowers. The purpose of these test was to obtain a better understanding of the variations which occur in service to enable better simulation of wheel stress analysis computer programs, improve laboratory dynamometer simulation of service conditions, and determine possible causes of thermal cracking of wheels in service. The results of these field tests are compared to tests previously conducted in service and in the laboratory.

It is generally understood that uneven heating of the tread of a wheel during braking is possible. A method has been devised to measure the intensity and frequency of hot spots on the wheel tread surface. After a description of the measurement apparatus and technique, results of a study of hot spots during constant speed brake applications with single composition shoes are presented. Possible lowering of the hot spot level by increasing the conformability of the brake shoe is studied by cutting one slot across each pad of a brake shoe. This method of hot spot study may be useful for future analysis and improvement of brake shoes.

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The mechanism of the formation of small cracks (thermal checks) that are formed as a result of two heat cycles is discussed. These thermal checks were noted in the treads of car wheels and careful examination of the conditions which caused them to form led to the development of a method of producing these thermal checks in a small specimen under better-controlled conditions. The reasons for the checks forming more readily in higher plain-carbon steel are discussed. Basically, the contraction of marten-site upon tempering seems to be the cause of the formation of thermal checks.