Experimental investigation on HCF strength affected by predamage from LCF of a near alpha titanium alloy
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Luo Yinyin Shanghai Electric Power Equipment Co., Ltd., Shanghai Steam Turbine Factory, Shanghai 200240, China
Shi Duoqia) and Yang Xiaoguang School of Energy and Power Engineering, Beihang University, Beijing 100191, China
Yu Huichen and Zhao Pengtao Beijing Institute of Aeronautical Materials, Beijing 100095, China (Received 11 July 2014; accepted 2 October 2014)
The feasibility of an accelerated test method on revealing the high cycle fatigue (HCF) limit stresses of a near alpha titanium alloy was successfully verified firstly during the rotary bending tests. The stress-controlled low cycle fatigue (LCF) tests at room temperature were then carried out over a range of maximum stresses and stress ratios to reveal the basic LCF strength. Finally, the core emphasis was focused on the influences of the predamage from LCF loadings on the subsequent HCF limit stresses corresponding to the life of 106 cycles. A total of eight levels of predamage from LCF with different stress levels, stress ratios, and proportions of LCF life were introduced, which resulted in obvious deterioration of the HCF stress limits (even under only 2% of expected LCF life). The fracture analysis exhibited that there were typical LCF failure characteristics in crack initiation regions of specimens under prior LCF loadings.
I. INTRODUCTION
With high frequency and low stress amplitude, high cycle fatigue (HCF) behavior requires a relatively large fraction of life to produce cracks of detectable sizes and leaves a very small fraction of life for propagation to failure. This trend results in unacceptable incidence of HCF-related failures in the aircraft engine industry over the past several years.1 Especially, in aeroengines, HCF behavior is generally caused by the high-frequency aerodynamic bending vibration loads2 and often combined with the in-service damage due to fretting, foreign object damage (FOD), or others. 1,3 The detailed information on the HCF capability of materials affected by such in-service damage was necessary.4 However, most existing studies on fatigue have been investigated under constant stress or strain amplitude conditions5–7 and during the typical operations of turbine engine, the gas turbine blades often suffer from the HCF load conditions combined with low cycle fatigue (LCF) damage caused by changes in operating speed of the engine disk.1 Hence, studies must be conducted to obtain a fundamental understanding of the interaction between these two types of loadings, and
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2014.309 2748
J. Mater. Res., Vol. 29, No. 22, Nov 28, 2014
http://journals.cambridge.org
Downloaded: 21 Mar 2015
the current study was focused on the influence of the predamage from LCF loadings on the HCF capability. Up to now, there have been limited studies of predamage from LCF cycling on the subsequent HCF limit stress. Ren and Nicholas1 studied the effects and mechanisms of various fractions of LCF predamage on subsequent HCF limit in Ni-based superalloy Udimet
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