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The low-cycle fatigue (LCF) deformation mechanism and fatigue life of an Al-12Si alloy were investigated at different temperatures and strain rates. With increasing temperature, the fatigue life increases at first and then reduces, which is derived from the deformation mechanism. At the lower temperatures, the primary Si cracking induced by piling-up of dislocations dominates fatigue damage behaviors. Both of increasing temperature and reducing the strain-rate can restrain the phase cracking, thus increase fatigue life. However, with further increasing temperature, the micro-scale void caused by dislocation annihilation dominates the phase debonding behavior, leading to the decrease of fatigue life.

The low cycle fatigue (LCF) damage mechanism and fatigue life of compacted graphite iron (CGI) at two strain rates were compared and analyzed at different temperatures. The results show that the strain rate has only little effect on the fatigue life of CGI at 25 °C, but the fatigue life reduces significantly with the decrease of strain rate at high temperatures (400 °C, 500 °C). The variation trend of fatigue life at 400 °C may be attributed to the initial cyclic hardening caused by the dynamic strain aging (DSA) effect combined with the serious damage localization of CGI. At 500 °C, the cyclic hardening is inhibited by serious oxidation. The fatigue life decreases with the decrease of strain rate can be ascribed to more oxidative damage and much serious grain boundary cracking. A prediction model for the fatigue life based on quadratic function relation was established through hysteresis energy and the variety of parameters (W0, β ) was explained by the corresponding damage mechanism. The quadratic relationships between the parameters and temperature can effectively predict the variation tendency of fatigue life versus temperature (0–650 °C).

High-cycle fatigue (HCF) and low-cycle fatigue (LCF) properties of a rolled AZ31-O alloy along different directions were evaluated at room temperature. Two types of samples denoted as RD (rolling direction) and TD (transverse direction) were compared because the samples along the two typical directions show an obvious anisotropy. By evaluating the fatigue parameters following the Manson–Coffin and Basquin’s equations, it is found that the fatigue lives of TD samples are longer than those of RD samples under both stress-controlled and strain-controlled cyclic loadings. Finally, the microscopic and macroscopic fracture features under tensile and fatigue loadings are observed and compared with the available literatures.

Methods to predict the S–N curves of high-strength steels in the very high cycle fatigue (VHCF) regime are reviewed. At the same time, a new prediction in form of Basquin’s equation is proposed based on the prediction of fatigue strengths in both high cycle fatigue regime and very high cycle fatigue regime. The new prediction is compared to the prior predictions and experiments results obtained by our recent experiment and others’ published papers.

The sizes of the "granular bright facet' (GBF) areas on fracture surfaces of specimens subjected to very high cycle fatigue for two high strength spring steels were measured in a field emission scanning electron microscope (FESEM) and compared with the estimated values, and a good agreement was found between the two sets of data. A criterion was proposed to estimate the sizes of GBF areas. It was assumed that when the increment of crack length in one applied stress cycle (numerically equal to crack growth rate, da/dN) is just equal to the plastic zone size in front of crack tip, r(p), the GBF stops developing. It means that hydrogen accumulating in the plastic zone under applied stress influences mostly on the fatigue behaviors which results in the morphology of GBF area quite different from the conventional fatigue fracture surface. The estimated sizes of GBF areas were also in accordance with the sizes measured from fracture surfaces of other high strength steels provided that the hydrogen concentration in those steels was not much higher than that in present spring steels. (c) 2007 Elsevier Ltd. All rights reserved.

The fatigue properties of four high strength steels with same strength class but containing different inclusion sizes were investigated using an ultrasonic fatigue testing machine in the gigacycle fatigue regime. The fracture surfaces were observed using field emission scanning electron microscopy (FESEM) and element distributions at the crack origins were measured by an electron probe rnicroanalyzer (EPMA). The fatigue behavior can be divided into three categories: (a) The S-N curve displays a Continuous decline and the internal cracks initiated from the large oxide inclusions for commercial 50CrV4 steel in which the average inclusion size is about 29 mu m. (b) Step-wise S-N curves were observed for clean 54SiCrV6 and clean 50CrV4 steels in which the average inclusion sizes are about 3.0 and 2.4 mu m respectively. Most fatigue failures originated from the VC inclusion clusters at the lower stress amplitudes. (c) For clean 54SjCr6 steel in which the inclusion size is smaller than 1 mu m the fatigue cracks did not initiated from inclusions or inclusion clusters but from the region enriched with carbon. S-N curve shows that the fatigue failure hardly Occurs from 10(6) to 10(9) cycles, in other words, the fatigue reliability can be substantially improved in the super long fatigue life regime. (c) 2006 Elsevier Ltd. All rights reserved.