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Effect of stress ratio on the Fatigue Crack Propagation Behavior of the Nickel-based GH4169 Alloy

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Acta Metallurgica Sinica(English Letters) 2017年第9期30卷 809-821页

作者： Shen Ye Jian-Guo Gong Xian-Cheng Zhang Shan-Tung Tu Cheng-Cheng Zhang Key Laboratory of Pressure Systems and Safety Ministry of EducationSchool of Mechanical and Power EngineeringEast China University of Science and TechnologyMeilongRoad 130Xuhui DistrictShanghai 200237People'sRepublic of China AECC Commercial Aircraft Engine Co.LTD ShanghaiEngineering Research Center for Commercial Aircraft EngineShanghai 201108People's Republic of China

The fatigue crack growth behavior of the newly developed GH4169 nickel-based alloy at a maximum stress of 700 MPa and different stress ratios was investigated in the present work employing the specimens with a single micro- notch at a frequency of 129 Hz at room temperature. The results demonstrate a typical three-stage process of fatigue crack propagation processing from the microstructurally small crack （MSC） stage to the physically small crack （PSC） stage, and finally to the long crack stage. The crack growth rate in the MSC stage is relatively high, while the crack growth rate in the PSC stage is relatively low. A linear function of crack-tip reversible plastic zone size was proposed to predict the crack growth rate, indicating an adequate prediction solution.

关键词： Fatigue crack Crack growth rate stress ratio Nickel-based alloy

Effects of stress ratio on the temperature-dependent high-cycle fatigue properties of alloy steels

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International Journal of Minerals,Metallurgy and Materials 2016年第12期23卷 1387-1396页

作者： Zhi-yang Lv Ao-shuang Wan Jun-jiang Xiong Kuang Li Jian-zhong Liu School of Transportation Science and Engineering Beihang UniversityBeijing 100191China Beijing Institute of Aeronautical Materials Beijing 100095China

This paper addresses the effects of stress ratio on the temperature-dependent high-cycle fatigue （HCF） properties of alloy steels 2CrMo and 9CrCo, which suffer from substantial vibrational loading at small stress amplitude, high stress ratio, and high frequency in the high-temperature environments in which they fimcfion as blade and rotor spindle materials in advanced gas or steam turbine engines. Fatigue tests were performed on alloy steels 2CrMo and 9CrCo subjected to constant-amplitude loading at four stress ratios and at four and three temperatures, respectively, to determine their temperature-dependent HCF properties. The interaction mechanisms between high temperature and stress ratio were deduced and compared with each other on the basis of the results of fractographic analysis. A phenomenological model was developed to evaluate the effects of stress ratio on the temperature-dependent HCF properties of alloy steels 2CrMo and 9CrCo. Good correlation was achieved between the predictions and actual experiments, demonstrating the practical and effective use of the proposed method.

关键词： alloy steel metal fatigue fatigue properties elevated temperature stress ratio

Effects of intermittent loading time and stress ratio on dwell fatigue behavior of titanium alloy Ti-6Al-4V ELI used in deep-sea submersibles

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Journal of Materials Science & Technology 2021年第18期77卷 223-236页

作者： Chengqi Sun Yanqing Li Kuilong Xu Baotong Xu State Key Laboratory of Nonlinear Mechanics Institute of MechanicsChinese Academy of SciencesBeijing100190China School of Engineering Sciences University of Chinese Academy of SciencesBeijing 100049China State Key Laboratory of Deep-sea Manned Vehicles(China Ship Scientific Research Center) Wuxi 214082China LuoyangShip Material Research Institute Luoyang471023China Aero Engine Corporation of China Beijing Institute of Aeronautical Materials Beijing 100095China

Different components of deep-sea submersibles,such as the pressure hull,are usually subjected to intermittent loading,dwell loading,and unloading during service.Therefore,for the design and reliability assessment of structural parts under dwell fatigue loading,understanding the effects of intermittent loading time on dwell fatigue behavior of the alloys is essential.In this study,the effects of the intermittent loading time and stress ratio on dwell fatigue behavior of the titanium alloy Ti-6 Al-4 V ELI were investigated.Results suggest that the dwell fatigue failure modes of Ti-6 Al-4 V ELI can be classified into three types,i.e.,fatigue failure mode,ductile failure mode,and mixed failure mode.The intermittent loading time does not affect the dwell fatigue behavior,whereas the stress ratio significantly affects the dwell fatigue life and dwell fatigue mechanism.The dwell fatigue life increases with an increase in the stress ratio for the same maximum stress,and specimens with a negative stress ratio tend to undergo ductile failure.The mechanism of dwell fatigue of titanium alloys is attribute to an increase in the plastic strain caused by the part of the dwell loading,thereby resulting in an increase in the actual stress of the specimens during the subsequent loading cycles and aiding the growth of the formed crack or damage,along with the local plastic strain or damage induced by the part of the fatigue load promoting the cumulative plastic strain during the dwell fatigue process.The interaction between dwell loading and fatigue loading accelerates specimen failure,in contrast to the case for individual creep or fatigue loading alone.The dwell fatigue life and cumulative maximum strain during the first loading cycle could be correlated by a linear relationship on the log–log scale.This relationship can be used to evaluate the dwell fatigue life of Ti alloys with the maximum stress dwell.

关键词： Ti-6Al-4V ELI Dwell fatigue Intermittent loading time stress ratio Creep fatigue interaction

Influence of stress ratio and Loading Condition on Near-threshold Fatigue Crack Growth Behaviour

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Journal of Materials Science & Technology 1993年第1期9卷 47-52页

作者： B.Weiss R.Stickler University of Vienna Wahringer Street 42A-1090 ViennaAustria

Near-threshold fatigue crack propagation behaviour of a cold-worked copper tested with distinct fa- tigue testing systems under different stress ratios has been investigated.The emphasis was placed on the evaluation of crack closure effect as well as the effective fatigue threshold,It was found that the fatigue threshold for R=0 is higher than those for R=-1 and R=0.4,for which almost the same threshold value was derived.Compared with the conventional closure evaluation method,the pro- posed new closure evaluation method can generally interpret the dependence of the fatigue thresh- old on stress ratio and loading condition,and leads to a higher and relatively constant effective fa- tigue threshold of about 3 MPa·m^(1/2) for the cold-worked copper at different stress ratios and loading conditions.

关键词： near-threshold fatigue crack stress ratio

EFFECTS OF stress ratio AND FREQUENCY ON CORROSION FATIGUE CRACK GROWTH MECHANISM IN LOW ALLOY STEELS

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Acta Metallurgica Sinica(English Letters) 1993年第6期6卷 373-378页

作者： HAN Enhou HAN KYumei ZHENG Yuli KE Wei Corrosion Science Laboratory,Institute of Corrosion and Protection of Metals,Academia Sinica,Shenyang,China postdoctoral,Institute of Corrosion and Protection of Metals,Academia Sinica,Shenyang 110015,China Inst of Corrosion and Protection of Metals Shenyang China

Based on theoretical analysis about local strain,strain rate and dissolving rate at crack tip, the corrosion fatigue crack growth rate of steels ZG20SiMn and SM50B-Zc in fresh water and 3.5% NaCl solution were measured experimentally,and the PH and electrode potential within crack were also measured continuously along with crack propagating.It showed that the increase of crack growth rate,caused by both decreasing frequency and raising stress ratio,was mainly accelerated by hydrogen embrittlement.

关键词： corrosion fatigue stress ratio crack growth electrode potential steel ZG20SiMn steel SM50B-Zc

Correlation of crack growth rate and stress ratio for fatigue damage containing very high cycle fatigue regime

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Theoretical & Applied Mechanics Letters 2012年第3期2卷 11-14页

作者： Chengqi Sun Youshi Hong State Key Laboratory of Nonlinear Mechanics Institute of MechanicsChinese Academy of SciencesBeijing 100190China

A model is proposed to correlate the crack growth rate and stress ratio containing very high cycle fatigue regime. The model is verified by the experimental data in literature. Then a formula is derived for the effect of mean stress on fatigue strength, and it is used to estimate the fatigue strength of a bearing steel in very high cycle fatigue regime at different stress ratios. The estimated results are also compared with those by Goodman formula.

关键词： very high cycle fatigue crack growth rate stress ratio fatigue strength

Effect of fiber-reinforcement on the mechanical behavior of sand approaching the critical state

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Journal of Rock Mechanics and Geotechnical Engineering 2022年第4期14卷 1241-1252页

作者： Jakhongirbek Ganiev Shotaro Yamada Masaki Nakano Takayuki Sakai Department of Civil Engineering Nagoya UniversityNagoya464-8603Japan Department of Civil Engineering Tohoku UniversitySendai980-8579Japan

Several types of ground improvement methods that employ fiber-reinforcement have been developed in recent years.A series of consolidated drained triaxial compression tests has been conducted here to examine the effect of short fibers on the mechanical properties of Toyoura sand.Sand with 0%,0.2%,0.4%,and 1%fiber contents,prepared to yield random distribution,was sheared under several confining pressures and controlled via their initial relative densities.The test results showed that the maximum and residual deviatoric stresses increased,whereas the volumetric expansion decreased with an increase in fiber content.Although the stress ratio h(=q/p′)and specific volume changed depending on the fiber content and confining pressure with shear progression,they each reached the same values for a definite fiber content at the end of shearing,independent of initial relative density.In other words,the unique critical state line can be found for a definite fiber content.Moreover,the greater the fiber content,the larger the slope of the critical state line at the end of shearing.Additionally,as the length of fibers shortened with the same percentage of fiber inclusions in sand,the deviatoric stress and the stress ratio decreased,approaching the shear-strain-volumetric response of unreinforced sand.

关键词： Fiber-reinforced sand Triaxial compression stress ratio Critical state Relative density

Behavior of High Water-cement ratio Concrete under Biaxial Compression after Freeze-thaw Cycles

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Journal of Wuhan University of Technology(Materials Science) 2008年第4期23卷 589-594页

作者： SHRUG Huaishuai SONG Yupu OU Jinpin State Key Laboratory of Structural Analysis for Industrial Equipment Dalian University of Technology Dalian 116024 China Shandong Provincial Academy of Building Research Jinan 250031 China State Key Laboratory of Coastal and Offshore Engineering Dalian University of Technology Dalian 116024 China

The high water-cement ratio concrete specimens under biaxial compression that completed in a triaxial testing machine were experimentally studied. Strength and deformations of plain concrete specimens in two loading direction under biaxial compression with stress ratio of a=0, 0.25, 0.5, 0.75, 1.0 were obtained after 0, 25, 50 cycles of freeze-thaw. Influences of freeze-thaw cycles and stress ratio on the peak stress and deformation of this point were analyzed according to the experimental results, Based on the test data, the failure criterion expressed in terms of principal stress after different cycles of freeze-thaw, and the failure criterion with consideration of the influence of freeze-thaw cycle and stress ratio were proposed respectively.

关键词： concrete freeze-thaw cycles stress ratio strength criteria

High-cycle fatigue behavior of Co-based superalloy 9CrCo at elevated temperatures

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Chinese Journal of Aeronautics 2016年第5期29卷 1405-1413页

作者： Wan Aoshuang Xiong Junjiang Lyu Zhiyang Li Kuang Du Yisen Chen Kejiao Man Ziyu School of Transportation Science and Engineering Beihang University

A modified model is developed to characterize and evaluate high-cycle fatigue behavior of Co-based superalloy 9CrCo at elevated temperatures by considering the stress ratio effect. The model is informed by the relationship surface between maximum nominal stress, stress ratio and fatigue life. New formulae are derived to deal with the test data for estimating the parameters of the proposed model. Fatigue tests are performed on Co-based superalloy 9CrCo subjected to con- stant amplitude loading at four stress ratios of -1, -0.3, 0.5 and 0.9 in three environments of room temperature （i.e., about 25 ℃） and elevated temperatures of 530 ℃ and 620 ℃, and the interaction mechanisms between the elevated temperature and stress ratio are deduced and compared with each other from fractographic studies. Finally, the model is applied to experimental data, demonstrating the practical and effective use of the proposed model. It is shown that new model has good correlation with experimental results.

关键词： Elevated temperature Fatigue Metals and alloys SEM stress ratio