Composite fatigue curve equation for assessing the fatigue resistance characteristics of press-fastened joints

Abstract

Press-fitted joints are quite technologically advanced and therefore have found wide application in many industries. In particular, they are widely used in shipbuilding, automotive manufacturing, railcar manufacturing, etc. While these connections have obvious advantages, they also have disadvantages, the main one being their low fatigue resistance, which is due to the effects of fretting corrosion. Existing calculation methods for assessing fatigue resistance characteristics cannot account for all the factors associated with the fretting corrosion process. For this reason, these characteristics are determined by fatigue testing of specimens or models. A distinctive feature of such tests is that, unlike conventional standard specimens, the life of pressed connections is determined over a cycle count exceeding 10 cycles. The use of common two-parameter fatigue curve equations, such as power and exponential, when applied to pressed connections leads to large errors, necessitating the search for other models. In particular, composite fatigue curves consisting of two sections governed by two different equations may be promising. This paper analyzes and discusses approaches to constructing a composite fatigue curve based on different assumptions. Methods for constructing a composite fatigue curve, the upper portion of which is governed by a power-law equation and the lower portion by the Weibull equation, are proposed, and specific examples of implementing these methods are provided. Newton's method and the wxMaxima software package were used to solve the resulting transcendental equations.