Cycle Fatigue Behavior Of Steels Research Articles

Effects of Natural Aging and Discontinuous Cyclic Loading on High Cycle Fatigue Behavior of Steels

Metallic components may not be used immediately and are stored for several months or years after fabrication in some cases, which experience long-term natural aging. Moreover, the fatigue-beared components commonly suffer discontinuous cyclic loadings in service. In this paper, the effects of natural aging and discontinuous loading on high cycle fatigue life and failure mechanism were investigated through rotating bending fatigue tests. The long-term natural aging (e.g., more than 20,000 h) reduced the fatigue life of both 25CrMo4 and 30CrMnSiA steels, and this effect was irrespective of the roughness of the specimen surface. The effect of natural aging on the failure mechanism was related to the microstructure of materials. The natural aging promoted the probability of multi-site crack initiation for 25CrMo4 steel, but had no influence on the crack initiation mode of 30CrMnSiA steel. The discontinuous cyclic loading had no harmful influence on the fatigue life of 25CrMo4 steel, and it had no influence on the failure mechanism. The specimens under continuous and discontinuous cyclic loadings both failed from single-site crack initiation or multi-site crack initiation at the specimen surface.

Effects of inclusions on the very high cycle fatigue behaviour of steels

AbstractThe very high cycle fatigue of high‐strength steels and many other alloys is controlled by the initiation and the propagation of cracks initiated at nonmetallic inclusions. Tiny cracks are early initiated from these inclusions. They propagate very slowly in a specific zone located close to the inclusion and called the fine‐grained area (FGA) or optical dark area. This area has a size of the order of that of the inclusion. The FGA is followed by the formation of conventional crack propagation area with the presence of striations in many cases. The details of initiation of these very high cycle fatigue cracks depend on the relative elastic and thermal properties of inclusions and matrix. The specificities of the FGA zone are dependent on the hydrogen segregated at the interface of the inclusions. An elasto‐plastic finite element calculation is performed to determine the residual stresses in the vicinity of the inclusions and to evaluate the effect of residual stresses.

Essential Characteristics and Frequency Effect for Very High Cycle Fatigue Behavior of Steels

With the increase of design fatigue life of many critical mechanical components and engineering structures, research on very high cycle fatigue (VHCF) has become a new topic for engineering components failure. This paper summarizes works of VHCF of high strength steel, such as the observations on fish-eye, which is one of the typical characteristics in VHCF regime; Characteristics of crack initiation and crack propagation are analyzed based on fracture surface; The present work also analyzes the fatigue mechanism and related models. Loading frequency effect on the VHCF behavior is also discussed. Some prospective aspects of future researches are proposed.

Prediction of Low Cycle Fatigue Lives of Low Alloy Steels.

An assessment of low cycle fatigue data was conducted in this paper with two new life prediction methods. A phenomenological method was developed that accounts for the flow characteristics as a result of loading in terms of dynamic viscosity. The other method is a statistical method known as Diercks equation that has been used as a first approximation of low cycle fatigue behavior of steels in the literature. The Diercks equation has been modified in this paper and life prediction analyses were conducted and compared against the other method. The phenomenological method predicted low cycle fatigue lives conservatively under different temperatures and strain rates whereas, modified Diercks equation had several limitations that were identified in this paper. Both the methods were found to correlate the low cycle fatigue data within the acceptable band of ±×2.