Abstract
It is not generally known or recognized that the flexural fatigue strength of a beam may be influenced to an appreciable extent by the shape of cross section of the member. In order to obtain further information on the magnitude of this shape effect, flexural fatigue tests were made employing four different shapes of cross section for each of two different steels. The results of these tests are compared and analyzed to clarify or explain some of the shape factors that may be of importance in affecting fatigue behavior. It is concluded that variations in residual stress or alterations of properties due to method of machining the different shapes play only a minor part in affecting the relative endurance limits. The susceptibility to localized inelastic action as governed by the shape of cross section and by the presence of “sore spots,” such as outward projecting corners, are tentatively believed to be the primary elements leading to the differences noted in flexural fatigue strengths.
