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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

In-situ observation and finite element analysis of fretting fatigue crack propagation behavior in 1045 steel

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Chinese Journal of Aeronautics 2021年第11期34卷 131-139页

作者： Qinan HAN Xusheng LEI Yue SU Shaoshi RUI Xianfeng MA Haitao CUI Huiji SHI Aero-engine Thermal Environment and Structure Key Laboratory of Ministry of Industry and Information Technology College of Energy and Power EngineeringNanjing University of Aeronautics and AstronauticsNanjing 210016China AML Department of Engineering MechanicsTsinghua UniversityBeijing 100084China AMPTL Department of Mechanical EngineeringTsinghua UniversityBeijing 100084China Sino-French Institute of Nuclear Engineering and Technology Sun Yat-Sen UniversityZhuhai 519082China

In this paper fretting fatigue crack behavior in 1045 steel is studied by in-situ observation and finite element analysis.in-situ fretting fatigue experiments are conducted to capture real-time fretting fatigue crack formation and propagation process.The fretting fatigue tests under different load conditions are carried out,then the lifetime and fracture surface are obtained.The crack propagation rates under different loading conditions are measured by in-situ observations.With in-situ observation,crack initiation location and direction are analyzed.Finite element model is used to calculate J-integral which then is applied to fitting with experimental crack growth rate,and establishing crack growth rate model.From fitted S-N curve,it turns out that smaller load ratio leads to higher lifetime.crack initiates slightly below the point equivalent to line contact of the contact surface in different test conditions,and crack direction shows no obvious relationship with load parameters.The established crack growth rate model well agrees with the test results.

关键词： crack growth rate Fretting fatigue In-situ observation J-integral 1045 steel

Investigation on Fracture Properties of Single-Flawed Tunnel Model Under Medium-to-Low-Speed Impacts

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Acta Mechanica Solida Sinica 2020年第2期33卷 205-225页

作者： Lei Zhou Zheming Zhu Ruifeng Liu Yong Fan Yuqing Dong Peng Ying State Key Laboratory of Hydraulics and Mountain River Engineering College of Architecture and EnvironmentSichuan UniversityChengdu 610065China Key Laboratory of Deep Underground Science and Engineering(Ministry of Education) College of Architecture and EnvironmentSichuan UniversityChengdu 610065China

Dynamic fractures occur frequently in geophysical processes and engineering applications.It is thus essential to study crack and failure behaviors,such as crack time-to-initiation,crack growth rate and arrest period under dynamic loading.In this study,impact experiments were implemented by utilizing the single-flawed tunnel specimens under drop-hammer impacts.Four brittle materials,i.e.,green sandstone,red sandstone,black sandstone and polymethyl methacrylate,were selected to make single-flawed tunnel specimens.Strain gauges and crack extension gauges were employed to measure the crack extension parameters.The properties of crack growth rate,crack time-to-initiation and arrest period of these four brittle materials were discussed and analyzed.The corresponding numerical simulation was performed by using the commercial software AUTODYN.The numerical results of crack growth rate and crack time-to-initiation agreed with the impact test results.The commercial software ABAQUS was applied to compute the dynamic stress intensity factors.The results show that both the dynamic initiation fracture toughness and the crack growth rate increase with the elastic moduli of these four types of brittle materials under the same loading conditions,whereas the crack time-to-initiation decreases with the increase in elastic moduli of the brittle materials under the same loading conditions.

关键词： Single-flawed tunnel Impact loading crack growth rate crack time-to-initiation Initiation fracture toughness

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

Integral inference method for da/dN-ΔK and P-da/dN-ΔK curves

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航空动力学报 2011年第6期26卷 1251-1256页

作者： FU Hui-min WU Qiong Research Center of Small Sample Technology Beijing University o~ Aeronautics and Astronautics Beijing 100191 China

The integral inference method for fatigue crack growth(FCG) curve was established based on the two-variance regression theory.The estimates of da/dN-ΔK curve and P-da/dN-ΔK curve with high confidence level and high survival probability were also given.FCG data scatter with stress intensity factor ranges in reality,which limits the group test method's application.The presented method analyzes FCG curve as an integration,thus it can exploit the lengthwise information among the FCG rates corresponding to different stress intensity factor ranges.Therefore,compared with group test method,the presented method can not only save specimens,but also have higher precision in the evaluations of da/dN-ΔK and P-da/dN-ΔK curves.

关键词： aero-engine fatigue crack growth(FCG) crack growth rate integral estimate reliability

A two-parameter model to predict fatigue life of high-strength steels in a very high cycle fatigue regime

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Acta Mechanica Sinica 2015年第3期31卷 383-391页

作者： Chengqi Sun Xiaolong Liu Youshi Hong The State Key Laboratory of Nonlinear Mechanics Institute of Mechanics Chinese Academy of Sciences

In this paper, ultrasonic （20 kHz） fatigue tests were performed on specimens of a high-strength steel in very high cycle fatigue （VHCF） regime. Experimental results showed that for most tested specimens failed in a VHCF regime, a fatigue crack originated from the interior of specimen with a fish-eye pattern, which contained a fine granular area （FGA） centered by an inclusion as the crack origin. Then, a two-parameter model is proposed to predict the fatigue life of high-strength steels with fish-eye mode failure in a VHCF regime, which takes into account the inclusion size and the FGA size. The model was verified by the data of present experiments and those in the literature. Furthermore, an analytic formula was obtained for estimating the equivalent crack growth rate within the FGA. The results also indicated that the stress intensity factor range at the front of the FGA varies within a small range, which is irrespective of stress amplitude and fatigue life.

关键词： Very high-cycle fatigue - High-strength steels Fatigue life Inclusion size crack growth rate

一种改进的裂纹扩展率单一曲线模型及模型指数确定

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Journal of Marine Science and Application 2022年第4期21卷 104-115页

作者：孙力黄瀛偲黄小平 State Key Lab of Ocean Engineering Shanghai JiaoTong UniversityShanghai200240China ShanghaiWaigaoqiao Shipbuilding Co. LTD.Shanghai 200137China

It is essential to precisely predict the crack growth,especially the near-threshold regime crack growth under different stress ratios,for most engineering structures consume their fatigue lives in this regime under random loading.In this paper,an improved unique curve model is proposed based on the unique curve model,and the determination of the shape exponents of this model is provided.The crack growth rate curves of some materials taken from the literature are evaluated using the improved model,and the results indicate that the improved model can accurately predict the crack growth rate in the nearthreshold and Paris regimes.The improved unique curve model can solve the problems about the shape exponents determination and weak ability around the near-threshold regime meet in the unique curve model.In addition,the shape exponents in the improved model at negative stress ratios are discussed,which can directly adopt that in the unique curve model.

关键词： Near-threshold regime crack growth rate Stress ratio Improved unique curve model Shape exponents

Effect of three dimensional stress state on unstable fracture condition and crack opening level in a new crack growth model

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Acta Metallurgica Sinica(English Letters) 2010年第1期23卷 41-49页

作者： Fang WANG Weicheng CUI China Ship Scientific Research Center Wuxi 214082 China

A new model for the analysis of fatigue crack growth in the metal structures was proposed. This model shows a promising capability of explaining various fatigue phenomena. The new crack growth model is further completed by a continuous empirical formula for estimating the value of variable fracture toughness during crack propagation and a modified continuous equation for the crack tip stress/strain constraint factor used to calculate the stress intensity factor at the opening level. The prediction results are proved to agree well with the observed phenomena in test.

关键词： Marine structures crack growth rate Three dimensional stress state Fracture toughness crack tip stress/strain constraint factor

A GENERAL CONSTITUTIVE RELATION FOR FATIGUE crack growth ANALYSIS OF METAL STRUCTURES

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Acta Metallurgica Sinica(English Letters) 2003年第5期16卷 342-354页

作者： W.C. Cui and X.P. HuangSchool of Naval Architecture & Ocean Engineering, Shanghai Jiaotong University, Shanghai 200030, China Sch. of Naval Arch. and Ocean Eng. Shanghai Jiaotong Univ. Shanghai 200030 China

crack growth rate curves are the fundamental material property for metal structures under fatigue loading. Although there are many crack growth rate curves available in the literature, few of them showed the capability to explain various special phenomena observed in tests. A modified constitutive relation recently proposed by McEvily and his co-workers showed very promising capability. This modified constitutive relation is further generalized by (1) introducing an unstable fracture condition; (2) defining a virtual strength to replace the yield stress; and (3) defining an overload and underload parameter. The performances of this general constitutive relation for fatigue crack growth is extensively studied and it is found that this general constitutive relation is able to explain various phenomena observed with particular strong capability on load sequence effect.

关键词： metal fatigue S-N curve crack growth rate general constitutive relation mean stress effect load sequence effect