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Pulsating tension fatigue tests were conducted at 25°C, 150°C, and 250°C to investigate the effect of temperature on high cycle and very high cycle fatigue behavior of titanium alloy. The fatigue strength decreases with the increase of temperature, and the surface failure is more sensitive to temperature than interior failure. Afterwards, the fatigue fracture morphology, microstructure, and texture of titanium alloy were characterized. The results show that the fracture of larger αp phase with the maximum shear stress and higher strain concentration is responsible for the facet formation. The formation of facets leads to the interior failure at different temperatures. Finally, combining with the definition of interior crack growth rate, an assessment approach was proposed to predict the crack growth rate within the inhomogeneous microstructure area (IMA), which takes crack growth acceleration caused by the increase of temperature into consideration. [ABSTRACT FROM AUTHOR]

The axial fatigue tests at elevated (650°C) temperature with stress ratios of 0.1 and −1 were conducted under the loading cycle range of 104–108 cycles to investigate interior cracking mechanism at elevated temperature of one selective laser melted GH4169 superalloy. Results showed that the interior fatigue crack nucleation was the main failure mode with both stress ratios at 650°C in the long‐life regime. The interior crack nucleation region consisting of many facets was formed under shear stress and strain according to the 3D morphology restructure of the fracture surface. Combined with the evaluation of the threshold stress intensity factor, the transition lengths from a small crack to a long crack for interior failure at both stress ratios were evaluated. Based on the above analysis, the microstructure‐related interior failure mechanism was summarized. Finally, crack nucleation and propagation lives were predicted to obtain the total fatigue life, which showed that the prediction and experimental data scattered between the factor‐of‐three boundaries. [ABSTRACT FROM AUTHOR]

High cycle fatigue and very high cycle fatigue tests with pulsating tension for three surface‐carburized steels were performed to investigate interior failure behavior and life prediction method. As a result, all cracks with fine granular area and fisheye characteristics are induced from inclusions in matrix or in carburized layer. However, the later cracking morphology is smoother, which is due to the difference of plastic deformation and microstructure of the two regions. Based on estimation of threshold values for small and long crack growth, fatigue design curves are established. The maximum inclusion sizes of three carburizing steels were estimated by four statistical analysis methods. Combined with material microstructure characteristics and the critical plane theory, a failure‐based life prediction model is proposed by using fatigue indicator parameter, whose validity is verified based on good agreement between predicted and experimental ones. [ABSTRACT FROM AUTHOR]