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Journal of Materials Science & Technology 2024年第6期173卷 247-260页

作者： Xiangnan Pan Leiming Du Guian Qian youshi hong State Key Laboratory of Nonlinear Mechanics Institute of MechanicsChinese Academy of SciencesBeijing 100190China

Fatigue failure can still occur beyond 107 cycles,***-high-cycle fatigue(VHCF),in many metallic materials,such as aluminium alloys and high-strength *** VHCF of high-strength steels,a fine granular area(FGA)surrounding an inclusion is commonly identified as the characteristic region of crack initiation on the fracture ***,no such FGA feature and related crack initiation behaviour were observed in VHCF of conventionally cast or wrought aluminium ***,we first reported the distinct mechanisms of crack initiation and early growth,namely the microstructure feature and the role of FGA in VHCF performance for an additively manufactured(AM)AlSi10Mg *** AM pores play a key role in fatigue crack initiation similar to that of the inclusions in high-strength steels,resulting in almost identical FGA behaviour for different materials under a range of mean stress with a stress ratio at R*** profile microstructure of FGA is identified as a nanograin layer with Si rearrangement and grain boundary *** process consumes a large amount of cyclic plastic energy making FGA undertake a vast majority of VHCF *** results will deepen the understanding of VHCF nature and shed light on crack initiation mechanism of other aluminium and AM alloys.

关键词： Aluminium alloy Additive manufacturing Nanograins Very-high-cycle fatigue(VHCF) Crack initiation Mean stress

A promising method for the analysis of notch effect on fatigue strength: Strain energy density approach

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Science China(Technological Sciences) 2016年第10期59卷 1617-1618页

作者： SUN ChengQi hong youshi Key Laboratory of Nonlinear Mechanics Institute of Mechanics Chinese Academy of Sciences University of Chinese Academy of Sciences

In recent years, the approach of strain energy density （SED） has received special attention in the analysis of notch effect on fatigue strength of notched components, e.g. ref. [1-3]. One of the fundamental contributions to SED-based approaches was by Sih [4,5] who proposed the SED factor S, which was defined as the product of the SED and a critical distance from the point of singularity. Thus, the failure is controlled by the critical value S~.

关键词：缺口效应疲劳强度密度法应变能强度影响 SED 参考文献临界距离

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

Feasibility study on buoyancy-weight ratios of a submerged floating tunnel prototype subjected to hydrodynamic loads

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Acta Mechanica Sinica 2015年第5期31卷 750-761页

作者： Xu Long Fei Ge youshi hong School of Mechanics Civil Engineering and ArchitectureNorthwestern Polytechnical University State Key Laboratory of Nonlinear Mechanics Institute of MechanicsChinese Academy of Sciences

The research progress of a novel traffic solution,a submerged floating tunnel（SFT）,is reviewed in terms of a study approach and loading *** existing publications,the buoyancy-weight ratio（BWR） is usually ***,BWR is a critical structural parameter that tremendously affects the dynamic behaviour of not only the tunnel tube itself but also the cable *** the context of a SFT prototype（SFTP） project in Qiandao Lake（Zhejiang Province,China）,the importance of BWR is illustrated by finite element analysis and subsequently,an optimized BWR is proposed within a reasonable range in the present *** the numerical model,structural damping is identified to be of *** damping and the corresponding Rayleigh coefficients are attained through a sensitivity study,which shows that the adopted damping ratios are fairly suitable for ***,the human sense of security is considered by quantifying the comfort index,which helps further optimize BWR in the SFTP structural parameter design.

关键词： Submerged floating tunnel Buoyancy-weight ratio Water wave and current loads Dynamic response Human security sense Comfort index

Dynamic shell buckling behavior of multi-walled carbon nanotubes embedded in an elastic medium

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Science China(Physics,Mechanics & Astronomy) 2013年第3期56卷 483-490页

作者： SUN ChengQi LIU KaiXin hong youshi State Key Laboratory of Nonlinear Mechanics Institute of MechanicsChinese Academy of Sciences LTCS and Department of Mechanics & Aerospace Engineering College of EngineeringPeking University

This paper studies the dynamic shell buckling behavior of multi-walled carbon nanotubes(MWNTs) embedded in an elastic medium under step axial load based on continuum mechanics *** is shown that,for occurrence of dynamic shell buckling of MWNTs or MWNTs embedded in an elastic medium,the buckling stress is higher than the critical buckling stress of the corresponding static shell buckling under otherwise identical *** results are demonstrated for dynamic shell buckling of individual double-walled carbon nanotubes(DWNTs) or DWNTs embedded in an elastic medium.A phenomenon is shown that DWNTs or embedded DWNTs in dynamic shell buckling are prone to axisymmetric buckling rather than non-axisymmetric *** results also indicate that the axial buckling form shifts from the lower buckling mode to the higher buckling mode with increasing buckling stress,but the buckling mode is invariable for a certain domain of buckling ***,an approximate analytic formula is presented for the buckling stress and the associated buckling wavelength for dynamic axisymmetric buckling of embedded *** effect of radii is also examined.

关键词： dynamic buckling carbon nanotube van der Waals forces buckling stress buckling mode

Effects of tension on vortex-induced vibration(ⅥⅤ) responses of a long tensioned cylinder in uniform flows

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Acta Mechanica Sinica 2017年第1期33卷 1-9页

作者： Ling Kang Fei Ge Xiaodong Wu youshi hong Institute of Mechanics Chinese Academy of SciencesNo. 15 Beisihuan Xi Road Beijing 100190 China

The effects of tension on vortex-induced vibration (VIV) responses for a tension-dominated long cylinder with an aspect ratio of 550 in uniform flows are experimentally investigated in this paper. The results show that elevated tension suppresses fluctuations of maximum displacement with respect to flow velocity and makes chaotic VIV more likely to appear. With respect to periodic VIV, if elevated tension is applied, the dominant vibration frequency in the in-line (IL) direction will switch from a fundamental vibration frequency to twice the value of the fundamental vibration frequency, which results in a ratio of the dominant vibration frequency in the IL direction to that in the cross-flow direction of 2.0. The suppression of the elevated tension in the fluctuation of the maximum displacement causes the axial tension to become an active control parameter for the VIV maximum displacement of a tension-dominated long riser or tether of an engineering structure in deep oceans. However, the axial tension must be optimized before being used since the high dominant vibration frequency due to the elevated tension may unfavorably affect the fatigue life of the riser or tether.

关键词： Tension effect Maximum displacement Dominant vibration frequency Chaos

An experimental investigation of dual-resonant and non-resonant responses for vortex-induced vibration of a long slender cylinder

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Science China(Physics,Mechanics & Astronomy) 2014年第2期57卷 321-329页

作者： WU XiaoDong GE Fei hong youshi College of Mechanics Taiyuan University of Technology State Key Laboratory of Nonlinear Mechanics Institute of MechanicsChinese Academy of Sciences

Experimental results of the dual-resonant and non-resonant responses are presented for vortex-induced vibrations(VIV)of a long slender *** cylinder has a diameter of 10mm and a length of 3.31 m,giving an aspect ratio of *** cylinder was towed by a carriage with the velocity up to 1.5 m/s,with the Reynolds number varying from 2500 to *** different weights were used to provide the initial *** resonance means that resonance occurs simultaneously in both the cross-flow(CF)and in-line(IL)*** experiments were conducted in two *** the first stage,dual-resonant dynamic features of the cylinder subjected to vortex-induced excitation were *** features of CF and IL vibration amplitude,motion orbits,phase angle differences,dominant frequencies and mode order numbers are *** the second stage of the experiments,particular emphasis was placed on non-resonant dynamic *** variation of multi-mode modal displacement amplitudes was investigated in detail.

关键词： vortex-induced vibrations long slender cylinder dual-resonant responses non-resonant responses

DYNAMIC BUCKLING BEHAVIOR OF MULTI-WALLED CARBON NANOTUBES SUBJECTED TO STEP AXIAL LOADING

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Acta Mechanica Solida Sinica 2012年第2期25卷 117-125页

作者： Chengqi Sun Kaixin Liu youshi hong State Key Laboratory of Nonlinear Mechanics Institute of MechanicsChinese Academy of SciencesBeijing 100190China LTCS and Department of Mechanics&Aerospace Engineering College of EngineeringPeking UniversityBeijing 100871China

This paper studies the dynamic buckling behavior of multi-walled carbon nanotubes （MWNTs） subjected to step axial loading. A buckling condition is derived, and numerical results are presented for MWNTs under fixed boundary conditions. It is shown that the critical buckling load of MWNTs is of multi-branches and decreases as the time elongates. The associated buckling modes for different layers of MWNTs can be either in-phase or out of phase, which is related to the branch that the critical buckling load belongs to. For MWNTs with the same innermost tube radius, the critical buckling load is decreased when increasing the layers.

关键词： multi-walled carbon nanotubes dynamic buckling van der Waals forces continuummechanics model

Effects of loading condition on very-high-cycle fatigue behaviour and dominant variable analysis

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Science China(Physics,Mechanics & Astronomy) 2014年第1期57卷 74-82页

作者： LEI ZhengQiang XIE JiJia SUN ChengQi hong youshi State Key Laboratory of Nonlinear Mechanics Institute of Mechanics Chinese Academy of Sciences PetroChina Pipeline R&D Center

The specimens of a high carbon chromium steel were quenched and tempered at 150℃, 180℃ and 300℃. Such specimens were tested via rotating bending and a push-pull type of axial loading to investigate the influences of loading condition on the behaviour of very-high-cycle fatigue （VHCF）. Experimental results show the different influences of inclusion size on the fa- tigue life for the two loading conditions. Predominant factors and mechanism for the fine-granular-area （FGA） of crack origin were discussed. In addition, a reliability analysis based on a modified Tanaka-Mura model was carried out to evaluate the sen- sitivity of inclusion size, stress, and AKFGA to the life of VHCF crack initiation.

关键词： very-high-cycle fatigue FGA loading condition life scatter inclusion

Flow-induced vibrations of long circular cylinders modeled by coupled nonlinear oscillators

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Science China(Physics,Mechanics & Astronomy) 2009年第7期52卷 1086-1093页

作者： GE Fei LONG Xu WANG Lei hong youshi State Key Laboratory of Nonlinear Mechanics Institute of MechanicsChinese Academy of SciencesBeijing 100190China

The dynamics of long slender cylinders undergoing vortex-induced vibrations (VIV) is studied in this work. Long slender cylinders such as risers or tension legs are widely used in the field of ocean engineering. When the sea current flows past a cylinder, it will be excited due to vortex shedding. A three-dimensional time domain model is formulated to describe the response of the cylinder, in which the in-line (IL) and cross-flow (CF) deflections are coupled. The wake dynamics, including in-line and cross-flow vibrations, is represented using a pair of non-linear oscillators distributed along the cylinder. The wake oscillators are coupled to the dynamics of the long cylinder with the acceleration coupling term. A non-linear fluid force model is accounted for to reflect the relative motion of cylinder to current. The model is validated against the published data from a tank experiment with the free span riser. The comparisons show that some aspects due to VIV of long flexible cylinders can be reproduced by the proposed model, such as vibrating frequency, dominant mode number, occurrence and transition of the standing or traveling waves. In the case study, the simulations show that the IL curvature is not smaller than CF curvature, which indicates that both IL and CF vibrations are important for the structural fatigue damage.

关键词： vortex-induced vibration (VIV) vortex-induced wave (VIW) wake oscillator long cylinder fluid-structure interaction