Fatigue Strength of Carbon-Steel Castings

Abstract

This paper summarizes the results of fatigue tests of round specimens of carbon-steel castings 10, 35, 50 and 100 mm in diameter. The specimens were tested under rotating bending, pulsating tension, and completely reversed tension and compression in order to investigate the effects of various defects on the fatigue strength. The various defects were all deliberately made and included artificially drilled holes, blowholes, and shrinkage cracks. The fatigue strength, the fatigue ratio, and the fatigue strength reduction factor were obtained from the fatigue test results of specimens having these various defects, and the fatigue strength of steel castings was compared with that of steel forgings. The following results were obtained. (1) The fatigue strength, the fatigue strength reduction factor, and the size effect on the fatigue strength are smaller in the case of steel castings than in the case of steel forgings. (2) The fatigue strength of specimens having artificially drilled holes is approximately equal to that of specimens having blowholes of the same size. (3) In the case of small blowholes (d/D<0.2) the size effect is extremely small. (4) There is a correlation between the defect ratio, obtained from radiographic inspection or fatigue fracture of the specimens, and the fatigue strength. (5) From these fatigue test results, we obtained the endurance limit diagram of carbonsteel castings under direct stress.